Fractional Excretion Research Articles

The role of ACT score in mepolizumab discontinuation

Background Mepolizumab is a therapy for severe asthma. We have little knowledge of the characteristics of people in the US that discontinue mepolizumab in clinical care. Objective To investigate the real-world efficacy and time to clinical discontinuation of mepolizumab, we evaluated individuals with asthma started on mepolizumab at the Cleveland Clinic. We hypothesized that individuals that discontinue mepolizumab have more severe and uncontrolled asthma at baseline. Methods Between 2016 and 2022, patients who started on mepolizumab consented to be assessed over 18 months. At baseline, a questionnaire including demographic and medical history was collected. Laboratory findings such as ACT score, FENO (Fractional Excretion of Nitric Oxide), and spirometry were recorded. At the conclusion of the observation period, the participants were divided into two categories: Group A and Group B. Results Group B [N = 28] discontinued mepolizumab (p < 0.05) at an average of 5.8 months (SD 4.2 months). Group A [N = 129] stayed on the therapy for at least 1 year. A participant with an ACT score less than 13 has an odds ratio of 6.64 (95% CI, 2.1 − 26.0) of discontinuing mepolizumab therapy. For a male, the odds of discontinuing mepolizumab therapy is 3.39 (95% CI, 1.1–11.2). Conclusion In this real-world study, we find that high eosinophil count may not be adequate in screening which individuals will benefit from mepolizumab. Up to 17% of patients fail therapy within 6 months, with male sex and low ACT score increasing risk of mepolizumab discontinuation at Cleveland Clinic.

Serum and Urinary Matrix Metalloproteinase-9 Concentrations in Dehydrated Horses.

Matrix metalloproteinase-9 is increased in renal tissue in human kidney disease, but its role as a biomarker for kidney disease has not been fully evaluated yet. The aim of this study was to evaluate serum MMP-9 (sMMP-9) and urinary MMP-9 (uMMP-9) concentrations in dehydrated horses. Dehydrated horses were prospectively included. Blood and urinary samples were taken at admission, and after 12, 24, and 48 h (t0, t12, t24, t48), an anti-equine MMP-9 sandwich ELISA was used. Four healthy horses served as the controls. Serum creatinine, urea, symmetric dimethylarginine (SDMA), urine-specific gravity, urinary protein concentration, fractional sodium excretion, and urinary gamma-glutamyl transferase/creatinine ratio (uGGT/Cr) were measured. Statistical analysis included a repeated measures ANOVA and mixed linear regression model. Overall, 40 dehydrated horses were included (mild dehydration 13/40, moderate 16/40, severe 11/40). Acute kidney injury was found in 1/40 horses; 7/40 horses showed elevated serum creatinine, 11/40 horses elevated serum SDMA, and 5/28 elevated uGGT/Cr at presentation. In dehydrated horses, sMMP-9 concentrations were significantly higher on t0 (median: 589 ng/mL, range: 172-3597 ng/mL) compared to t12 (340 ng/mL, 132-1213 ng/mL), t24 (308 ng/mL, 162-1048 ng/mL), and t48 (258 ng/mL, 130-744 ng/mL). In healthy horses, sMMP-9 (239 ng/mL, 142-508 ng/mL) showed no differences over time or compared to patients. uMMP-9 and uMMP-9/creatinine did not differ over time or to the controls. No differences were found between dehydration groups. Urinary casts (p = 0.001; estimate = 135) and uGGT/Cr (p = 0.03; estimate = 6.5) correlated with sMMP-9. Serum urea was associated with uMMP-9/Cr (p = 0.01, estimate 0.9). In conclusion, sMMP-9 was elevated at arrival in dehydrated patients compared to later measurements. Correlations to uGGT/Cr and urinary casts need further evaluation.

Ketone production and excretion even during mild hyperglycemia and the impact of sodium-glucose co-transporter inhibition in type 1 diabetes

AimsWe aimed to determine if ketone production and excretion are increased even at mild fasting hyperglycemia in type 1 diabetes (T1D) and if these are modified by ketoacidosis risk factors, including sodium-glucose co-transporter inhibition (SGLTi) and female sex. MethodsIn secondary analysis of an 8-week single-arm open-label trial of empagliflozin (NCT01392560) we evaluated ketone concentrations during extended fasting and clamped euglycemia (4–6 mmol/L) and mild hyperglycemia (9–11 mmol/L) prior to and after treatment. Plasma and urine beta-hydroxybutyrate (BHB) concentrations and fractional excretion were analyzed by metabolomic analysis. ResultsForty participants (50 % female), aged 24 ± 5 years, HbA1c 8.0 ± 0.9 % (64 ± 0.08 mmol/mol) with T1D duration of 17.5 ± 7 years, were studied. Increased BHB production even during mild hyperglycemia (median urine 6.3[3.5–13.6] vs. 3.5[2.2–7.0] µmol/mmol creatinine during euglycemia, p < 0.001) was compensated by increased fractional excretion (0.9 % [0.3–1.6] vs. 0.4 % [0.2–0.9], p < 0.001). SGLTi increased production and attenuated the increased BHB fractional excretion (decreased to 0.3 % during mild hyperglycemia, p < 0.001), resulting in higher plasma concentrations (increased to 0.21 [0.05–0.40] mmol/L, p < 0.001), particularly in females (interaction p < 0.001). ConclusionsEven mild hyperglycemia is associated with greater ketone production, compensated by urinary excretion, in T1D. However, SGLTi exaggerates production and partially reduces compensatory excretion, particularly in women.

Fractional excretion of urea nitrogen can identify true worsening renal function in patients with acute heart failure

Abstract Background Worsening renal function (WRF) often occurs during decongestive treatment in acute heart failure (AHF). Although WRF has previously been associated with worse prognosis, recent studies have revealed that it may not contribute to an unfavorable outcome in the setting of adequate decongestion achieved. Therefore, there is growing interest to identify patients who develop "true WRF" with poor outcomes. Purpose Fractional excretion of urea nitrogen (FEUN), which is used to differentiate causes of renal failure, has emerged as a surrogate marker of volume status in patients with AHF complicated by renal dysfunction. Recent study has reported that a low FEUN value (FEUN ≤32.1%) represents intravascular dehydration, whereas a high FEUN value (FEUN &amp;gt;38.0%) reflects intravascular congestion, both being independent adverse prognostic factors. Therefore, we hypothesized that FEUN could identify "true WRF" in patients with AHF. Methods We examined 801 hospitalized patients with AHF and renal dysfunction (defined as discharge estimated glomerular filtration rate &amp;lt;60 mL/min/1.73 m²) whose FEUN was measured at discharge. The patients were divided into four groups as follows: no WRF (n=683); WRF with low FEUN (≤32.1%) (n=36); WRF with medium FEUN (&amp;gt;32.1% and ≤38.0%) (n=25); and WRF with high FEUN (&amp;gt;38.0%) (n=57). WRF was defined as an increase in serum creatinine ≥0.3 mg from admission to discharge. FEUN was calculated by the following formula: (urinary urea × serum creatinine) × 100 / (serum urea × urinary creatinine). The primary endpoint was the composite of all-cause death and heart failure (HF) readmission within 1-year after discharge. Results Regarding baseline characteristics, the WRF with low FEUN group had lower left ventricular ejection fraction, whereas the WRF with high FEUN group had poorer renal function. During the median follow-up period of 300 days, 18 all-cause deaths and 165 HF readmissions occurred. Kaplan–Meier analysis showed that patients without WRF had a significantly higher event-free survival rate than those with WRF. In addition, the WRF with medium FEUN group had a significantly higher event-free survival rate similar to that of the no WRF group, whereas the WRF with low FEUN and WRF with high FEUN groups had lower event-free survival rates. In multivariable Cox regression analysis, the WRF with low FEUN (hazard ratio, 1.91; 95% confidence interval, 1.02–3.57; P=0.043) and WRF with high FEUN (hazard ratio, 1.71; 95% confidence interval, 1.02–2.89; P=0.043) groups were independently associated with poor outcomes, even after adjusting for confounders. Conclusion Our study suggests that FEUN can identify prognostically relevant WRF and may be a useful marker for guiding decongestive therapy in patients with AHF complicated by WRF.Table 1Figure 1

Urinary biomarkers in different diuretic response groups with heart failure

Abstract Purpose Predicting diuretic response in different hemodynamic profiles is challenging in heart failure patients. Worsening renal function with diuretic therapy leads to decision making more difficult. Spot urinary sodium is an important milestone to determine decongestion therapy intensity. Serum biomarkers are widely used for diagnosis and follow up but more urinary biomarkers can be identified for risk stratification. Methods We enrolled 61 patients with decompansated heart failure on the first day of admission. Baseline characteristics and urinary biomarkers were recorded. Diuretic response was classified as good or poor response groups according to spot urine sodium within second hour after first intravenous diuretic administration. Quantitative variables were specified as mean ± standard deviation, categorical variables were specified as frequency and percentage. Mean differences were assessed with Student-T test and Welch test. Statistically significant parameters were also assessed with logistic regression analysis. Results Only U/P creatinine ratio and urine creatinine were statistically lower in good diuretic response group (p&amp;lt;0.0001). Fractional excretion of urea and potassium were higher in good response group (p&amp;lt;0.0001 and p&amp;lt;0.005). Urinary sodium to potassium ratio, UNa/UCr and UK/UCr are also statistically higher in the good response group (p&amp;lt;0.0001). Sodium associated parameters (UNa/UK, UNa/UCr) and urinary creatinine were also significant in logistic regression. Discussion Urinary biomarkers are not well defined parameters in heart failure patients but these parameters may be more dynamic than serum parameters as spot urine sodium. Our data indicates that poor response group has a more prerenal phenotype than good response group.Table 1.Urine biomarker definitionsTable 2.Results

Quantitative Metabolism and Urinary Elimination Kinetics of Seven Neonicotinoids and Neonicotinoid-Like Compounds in Humans.

Reverse dosimetry, i.e., calculating the dose of hazardous substances that has been taken up by humans based on measured analyte concentrations in spot urine samples, is critical for risk assessment and requires metabolic and kinetic data. We quantitatively studied the metabolism of seven major neonicotinoid and neonicotinoid-like compounds (NNIs) after single oral doses in male volunteers and determined key kinetic parameters and urinary elimination for NNIs together with their metabolites. Complete and consecutive urine samples were collected over 48 h. All samples were analyzed by tandem mass spectrometry, following liquid or gas chromatographic separation. Single- and group-specific NNI metabolites were quantified, i.e., hydroxylated and N-dealkylated NNIs and NNI-associated carboxylic acids and their glycine derivatives. Large, substance-dependent variations of key toxicokinetic parameters were observed. Mean times of concentration maxima (tmax) in urine varied between 2.0 (imidacloprid) and 25.8 h (N-desmethyl-clothianidin), whereas mean urinary elimination half-times (t1/2) were between 2.5 (acetamiprid) and 49.5 h (sulfoxaflor). Mean 48 h excretion fractions (Fue's) were between 0.03% (2-chloro-1,3-thiazole-5-carboxylic acid glycine) and 84% (clothianidin). In contrast, the interindividual differences of Fue's between the volunteers for each of the NNIs and their metabolites remained low (below a factor of 2 between the maximum and minimum derived Fue with the exception of 6-chloronicotinic acid in the acetamiprid dose study). The obtained quantitative data enabled choosing appropriate biomarkers for exposure assessment and, at the same time, for risk assessment by reverse dosimetry at current environmental exposures, i.e., comparing the calculated doses that have been taken up to currently available acceptable daily intakes of NNIs.

Role of Glycosuria in SGLT2 Inhibitor-Induced Cardiorenal Protection: A Mechanistic Analysis of the CREDENCE Trial.

SGLT2 inhibitors have been shown to provide pronounced reductions in cardio-renal outcomes, including cardiovascular death, heart failure, and renal failure. The mechanisms underlying these benefits remain uncertain. We hypothesized that the effects could be attributed to the elevated glycosuria induced by these drugs. Urine concentrations of glucose, creatinine, and ketones were measured at baseline and after 1-year treatment with either placebo or canagliflozin 100mg/day in ∼2600 individuals from the CREDENCE trial (enrolling patients with type 2 diabetes, chronic kidney disease, and albuminuria). Associations between glycosuria and the primary composite endpoint from CREDENCE and secondary outcomes were assessed using Cox proportional hazards models. Canagliflozin treatment increased fractional urinary glucose excretion from 3±9% at baseline to 30±26% at year 1 (vs 5±19% with placebo, p<0.001). Subjects on canagliflozin and in the top quartile of urine glucose/creatinine ratio at year 1 were significantly protected for the primary endpoint (HR=0.42 [95% C.I.:0.30-0.61]); similar results were seen for hospitalized heart failure (HR=0.45 [0.27-0.73]) and all-cause death (HR=0.56 [0.39-0.80]). These associations persisted on adjustments for multiple conventional risk factors. In patients with T2D and CKD treated with canagliflozin, individuals with the highest amount of glycosuria showed the strongest protection against multiple cardio-renal outcomes.

Tubular dysfunction impairs renal excretion of pseudouridine in diabetic kidney disease.

Plasma nucleosides-pseudouridine (PU) and N2N2-dimethyl guanosine (DMG) predict the progression of type 2 diabetic kidney disease (DKD) to end-stage renal disease, but the mechanisms underlying this relationship are not well understood. We used a well-characterized model of type 2 diabetes (db/db mice) and control nondiabetic mice (db/m mice) to characterize the production and excretion of PU and DMG levels using liquid chromatography-mass spectrometry. The fractional excretion of PU and DMG was decreased in db/db mice compared with control mice at 24 wk before any changes to renal function. We then examined the dynamic changes in nucleoside metabolism using in vivo metabolic flux analysis with the injection of labeled nucleoside precursors. Metabolic flux analysis revealed significant decreases in the ratio of urine-to-plasma labeling of PU and DMG in db/db mice compared with db/m mice, indicating significant tubular dysfunction in diabetic kidney disease. We observed that the gene and protein expression of the renal tubular transporters involved with nucleoside transport in diabetic kidneys in mice and humans was reduced. In conclusion, this study strongly suggests that tubular handling of nucleosides is altered in early DKD, in part explaining the association of PU and DMG with human DKD progression observed in previous studies.NEW & NOTEWORTHY Tubular dysfunction explains the association between the nucleosides pseudouridine and N2N2-dimethyl guanosine and diabetic kidney disease.

Fractional Excretion of Urinary Sodium and Urinary Sediment Microscopy for Prediction of Response to Vasoconstrictors in Hepatorenal Syndrome Type 1

Fractional Excretion of Urinary Sodium and Urinary Sediment Microscopy for Prediction of Response to Vasoconstrictors in Hepatorenal Syndrome Type 1

Fractional Excretion of Urea for the Differential Diagnosis of AKI: A Systematic Review and Meta-Analysis with Comparison to Fractional Excretion of Sodium

Fractional Excretion of Urea for the Differential Diagnosis of AKI: A Systematic Review and Meta-Analysis with Comparison to Fractional Excretion of Sodium

Endostatin and Cystatin C as Potential Biomarkers for Early Prediction of Preeclampsia.

Preeclampsia (PE) is characterized by new onset hypertension and proteinuria. Undoubtedly, some individuals do not fit precisely into this description, and it could be challenging to spot newly developed PE in females who already have hypertension or renal illness. Monitoring the disease's progression enables the optimization of delivery time while minimizing premature births. The current study explores the diagnostic benefits of serum endostatin and cystatin C in addition to serum and urinary magnesium (Mg) and fractional excretion magnesium (FEMg) for early prediction of PE. The population sample included 82 pregnant women divided into 3 groups: normal pregnancy group served as a control (n = 26), nonpreeclampsia (NPE, n = 34) group included pregnant women with one or more risk factors but did not progress to PE, and pregnant women who developed preeclampsia (PE, n = 22) group. Blood samples were withdrawn at two sampling times: at 12th to 16th and 24th to 26th weeks of gestation. Compared to normal pregnancy, results (X̅ ± SD) indicated a significant increase in serum endostatin in NPE at the first sample (10.78 ± 3.63 ng/mL) and the second sample (28.03 ± 3.79 ng/mL), while cystatin C was at the first sample (0.68 ± 0.06 mg/dL) and the second sample (0.71 ± 0.07 mg/dL). In the PE group, the serum endostatin was 18.86 ± 4.37 ng/mL at the first sampling time and 53.56 ± 9.76 ng/mL for the second sample. Serum cystatin C was also elevated in PE with X̅ ± SD equivalent to 0.73 ± 0.08 and 0.89 ± 0.08 mg/dL at the first and second samples, respectively. On the other hand, serum and urinary Mg in addition to FEMg levels did not significantly differ across the groups under study. Receiver operating characteristic (ROC) curve analysis proved that both endostatin and cystatin C could be good indicators for PE. The findings imply that measuring endostatin and cystatin C at early pregnancy and before progression to PE may be effective in detecting the likelihood of PE. Endostatin could be more precise and sensitive in assessing the probability of PE than cystatin C; however, coupling of the two parameters may be promising.

Mathematical solutions in internal dose assessment: A comparison of Python-based differential equation solvers in biokinetic modeling

In biokinetic modeling systems employed for radiation protection, biological retention and excretion have been modeled as a series of discretized compartments representing the organs and tissues of the human body. Fractional retention and excretion in these organ and tissue systems have been mathematically governed by a series of coupled first-order ordinary differential equations (ODEs). The coupled ODE systems comprising the biokinetic models are usually stiff due to the severe difference between rapid and slow transfers between compartments. In this study, the capabilities of solving a complex coupled system of ODEs for biokinetic modeling were evaluated by comparing different Python programming language solvers and solving methods with the motivation of establishing a framework that enables multi-level analysis. The stability of the solvers was analyzed to select the best performers for solving the biokinetic problems. A Python-based linear algebraic method was also explored to examine how the numerical methods deviated from an analytical or semi-analytical method. Results demonstrated that customized implicit methods resulted in an enhanced stable solution for the inhaled 60Co (Type M) and 131I (Type F) exposure scenarios for the inhalation pathway of the International Commission on Radiological Protection (ICRP) Publication 130 Human Respiratory Tract Model (HRTM). The customized implementation of the Python-based implicit solvers resulted in approximately consistent solutions with the Python-based matrix exponential method (expm). The differences generally observed between the implicit solvers and expm are attributable to numerical precision and the order of numerical approximation of the numerical solvers. This study provides the first analysis of a list of Python ODE solvers and methods by comparing their usage for solving biokinetic models using the ICRP Publication 130 HRTM and provides a framework for the selection of the most appropriate ODE solvers and methods in Python language to implement for modeling the distribution of internal radioactivity.

Lessons to be learned from real life data from 98 gout patients using benzbromarone

Aim: This study aims to analyze the efficacy and safety of benzbromarone as uricosuric, in a real-life clinical setting of a retrospective hospital-based gout cohort. Methods: Data from gout patients were retrieved from the digital hospital dossiers. Demographics, clinical variables, and laboratory parameters were collected at baseline and 6 months. Efficacy was measured by reaching a serum uric acid (sUA) target &lt; 0.30 mmol/L at 6 months, and the fractional excretion of uric acid (FeUA) was used as a parameter with a potential predictor value. Results: Data from 98 gout patients were analyzed. Patients were 70 (± 12) years of age, and 90% were male. After 6 months of treatment, 68 out of 98 patients (69%) reached a sUA level &lt; 0.30 mmol/L (5 mg/dL). In patients with a FeUA &lt; 4.5%, so-called low excretors, the FeUA increase was most impressive from 3.2% (± 1.0%) to 12.1% (± 6.9%) after 6 months of benzbromarone treatment (mean increase +8.9% [95% confidence interval (CI): +6.5 to +11.5%], P &lt; 0.001). In non-low excretors, FeUA was on average 7.3% (± 5.1%) and increased to 9.7% (± 6.1%): a mean +2.1% change (95% CI: –2.2 to +6.6%). The increase differed insignificantly in low versus non-low excretors: P &gt; 0.05. Four patients stopped benzbromarone treatment because of a progressive decline in renal function, a condition that was already present before benzbromarone was initiated. Remarkably 38% of patients still using benzbromarone after 3.8 (± 3.4) years of treatment. Conclusions: Using the uricosuric benzbromarone in real-life gout patients proved effectivity in lowering sUA levels within 6 months by increasing FeUA significantly. Particularly low excretors benefit from benzbromarone treatment manipulating this mode of action. Determining FeUA in gout patients may further help to find the patient profile benefiting the most from benzbromarone treatment.

Genetic and clinical characterization of familial renal glucosuria.

Familial renal glucosuria (FRG) is a hereditary disorder caused by variants in SLC5A2 encoding sodium-glucose cotransporter 2 (SGLT2). In this study, we aimed to characterize proximal tubule solute transport, glucagon secretion and the genotype-phenotype relationship in FRG patients. We sequenced SLC5A2 and PDZK1IP1 in 21 FRG patients and measured the renal threshold of glucose (RTG) in 15 patients. We built an open-source online calculator of RTG, evaluated the proximal tubule transport of amino acid, uric acid and phosphate, and explored glucagon secretion after glucose ingestion in FRG patients. We identified 12 novel SLC5A2 variants (G484D, R564W, A212S, c.574+1G>C, W649*, S592Cfs*6, Q579*, Y339*, V39F, G491E, A464E and G360D) in our cohort and yielded 111 SLC5A2 variants from literature review. RTG in our cohort ranged from 1.0 to 9.2mmol/L. Patients with two SLC5A2 variants had lower RTG (3.9 vs 6.2mmol/L) and higher 24-h urinary glucose excretion (24hUG) than single-variant carriers (291.0 vs 40.0mmol/1.73 m2). Patients with homozygous missense or in-frame indels had mean 24hUG of 457.2mmol/1.73 m2, comparable to those with homozygous truncating variants (445.0mmol/1.73 m2) and significantly more than those with homozygous splicing variants (196.6mmol/1.73 m2). Patients with homozygous missense variants involving conservative residues (582.0mmol/1.73 m2) had more 24hUG than those with variants at non-conservative residues (257.6mmol/1.73 m2). Four out of 14 tested patients had mild aminoaciduria. The RTG of FRG patients had no significant correlation to phosphate reabsorption but a potential negative correlation to the fractional excretion of uric acid. Postprandial suppression of glucagon secretion was absent in most FRG patients. We built a comprehensive map showing the impact of SLC5A2 variant type and variant location on glucosuria severity. Our results highlighted the role of key residues in maintaining the transport function of SGLT2 and the functional link between glucosuria and reabsorption of amino acid and uric acid in FRG patients.

Contribution of thick ascending limb and distal convoluted tubule to glucose-induced hypercalciuria in healthy controls.

Carbohydrates increase kidney stone risk and increase urine calcium and magnesium. We hypothesize that the effects of glucose as an allosteric modulator of calcium-sensing receptors may mediate this effect. Six healthy subjects were on a low-sodium diet before consuming 100 g of glucose beverage. Timed fasting (3) and postglucose (6) urine and blood samples were collected every 30 min. Urine composition and serum markers were measured and microvesicular abundance of tubular transport proteins (NHE3, NKCC2, NCC, and TRPV5) were quantified. Postglucose, serum glucose, and insulin rose rapidly with a parallel increase in calcium and magnesium excretion and no change in fractional excretion of sodium. Both serum parathyroid hormone (PTH) and urine TRPV5 fell in the postglucose periods. The rise in the calcium and magnesium excretion likely occurred primarily in the thick ascending limb where they are both under control of the calcium-sensing receptor. The fall in PTH and TRPV5 support the role of glucose as an allosteric modulator of calcium-sensing receptor.NEW & NOTEWORTHY Sugar increases urine calcium and magnesium as well as kidney stone and bone disease risk. Our study provided new insights into the underlying mechanism as we gave healthy subjects an oral glucose load and used newer tools such as fractional excretion of lithium, serum parathyroid hormone, and microvesicular abundance of tubular transport proteins to characterize the mechanism and identify the thick ascending limb with possible calcium-sensing receptor mediation as a likely contributor to this mechanism.

SAT250 A Case Of Hypercalcemia In Pregnancy - A Diagnostic And Management Challenge

Abstract Disclosure: W. Cheng: None. Y. Kuan: None. Hypercalcemia in pregnancy is rare and poses significant diagnostic and management challenges especially in a low resource setting. Although primary hyperparathyroidism (PHPT) is the main cause, physiological changes in calcium homeostasis make it difficult to distinguish from familial hypocalciuric hypercalcemia (FHH) unless genetic testing is done. Furthermore uncertainty exists on the safety of pharmacotherapy for hypercalcemia in pregnancy which if untreated, can be detrimental to both mother and child. Described herein a 17 year-old primigravida who presented at 32 weeks of gestation for asthma exacerbation precipitated by COVID-19 infection. She was incidentally found to have PTH-dependent hypercalcemia with albumin-corrected calcium 3.42 mmol/L [2.10-2.55] associated with raised intact parathyroid hormone (iPTH) 15 pmol/L [1.6 - 6.0] and deficient serum 25OH Vitamin D at 19.95 nmol/L [50-125]. She was given IV saline of 3-3.5L/day but to no avail as her serum calcium was persistently above 3 mmol/L with an episode of premature uterine contraction. Calcitonin was given in short courses and withheld once albumin-corrected calcium dropped below 3 mmol/L but rebound within three days. As bisphosphonates is contraindicated in pregnancy, we introduced cinacalcet, up to 75mg/day after discussion with the patient and her family. Meanwhile, investigations were done to ascertain underlying cause. Fractional urine calcium excretion ranged from 0.0068 (spot urine sample) to 0.0568 (24-hour urine sample). Ultrasound neck did not reveal enlarged parathyroid glands or an adenoma. Sestamibi scan was contraindicated in pregnancy. Genetic testing for FHH was too costly but all her first-degree relatives tested to have normocalcemia. Blood pressure remained normal throughout pregnancy. She was discharged with cinacalcet at calcium level of 2.7 mmol/L. However she defaulted follow-up and medications and presented at 36 weeks of gestation for preterm labour. She gave birth to a healthy, 2.46kg baby girl. The baby had neonatal jaundice but normal calcium level. Postpartum, the patient was asymptomatic despite persistent hypercalcemia 3.12 - 3.15nmol/L. As she was non-compliant to cinacalcet it was stopped and serum calcium did not worsen. Sestamibi scan is planned after she stops breastfeeding and a reassessment of the urine calcium once vitamin D is adequately replenished. She refused exploratory parathyroidectomy. She continued to be followed up at the endocrine clinic while her baby at primary care. Contraception is advised untill definitive diagnosis and treatment of hypercalcemia. This case illustrates the challenges in managing hypercalcemia in pregnancy and difficulty in distinguishing PHPT vs FHH without genetic testing. Presentation: Saturday, June 17, 2023

THU464 An Uncommon Case Of Adult-Onset Hypophosphatemic Osteomalacia

Abstract Disclosure: P.M. Lockhart Pastor: None. N.M. Maalouf: None. Introduction: Hypophosphatemic conditions that interfere with bone mineralization and cause osteomalacia comprise many hereditary and acquired diseases. We describe a case of acquired hypophosphatemic osteomalacia associated with Multiple Myeloma (MM). Case Report: A 45-year-old man with MM and systemic AL amyloidosis was referred to our clinic for evaluation of low bone mass on DXA scan. He presented with progressive back pain, proximal muscle weakness, weight loss, and worsening proteinuria, eventually leading to the diagnosis of AL amyloidosis on fat pad biopsy and MM on bone marrow biopsy. Biochemical work up was remarkable for elevated serum alkaline phosphatase at 463 U/L (reference range 46-116) determined to be of skeletal origin. Additional studies included serum phosphorus 1.9 mg/dl (2.4-4.5), creatinine 1.0 mg/dl (0.7-1.2), calcium 9.0 mg/dl (8.4-10.2), albumin 4.1 g/dl (3.5-5.2), PTH 17.1 pg/ml (15-77), and 25-OH-D 52 ng/ml (30-80). Skeletal survey and PET/CT identified diffuse osteopenia but no fracture or lytic lesion. DXA scan showed Z-score of -5.0 at the L-spine and -4.2 at the femoral neck. Further work-up of hypophosphatemia was notable for fractional excretion (FE) phosphate of 37% (&amp;lt;20), serum 1,25-OH2-D 74 pg/ml (18-64), FGF-23 &amp;lt;14 pg/ml (&amp;lt;59), hypouricemia with high FE uric acid, and normoglycemia with glucosuria. Given his marked bone pain, hypophosphatemia, hypouricemia, glucosuria, and elevated alkaline phosphatase, he was diagnosed with hypophosphatemic osteomalacia presumably secondary to light chain accumulation in kidneys leading to proximal tubule dysfunction (acquired Fanconi syndrome). In addition to MM treatment (5 cycles of Dara-CyBorD then stem cell transplantation), he was started on phosphate supplementation, with marked improvement in bone pain, muscle strength, and serum alkaline phosphatase over 6 months. No anti-resorptive agents were used in treating his MM. Conclusion: This case highlights an unusual presentation of hypophosphatemic osteomalacia. It is important to recognize that bone pain in patients with MM is not only caused by osteolytic lesion but can also result from osteomalacia due to Fanconi syndrome due to light chain kappa deposition. In this patient, treatment with phosphate supplementation resulted in clinical improvement of bone pain and biochemical markers. To date, there are only few reported cases of hypophosphatemic osteomalacia due to Fanconi syndrome in the setting of MM. Presentation: Thursday, June 15, 2023

THU406 24-hydroxylase Deficiency, A Rare Cause Of Hypercalcemia

Abstract Disclosure: J. Hodge: None. M. Gortakowski: None. N. Barua: None. Background: 24-hydroxylase is encoded by CYP24A1 and functions to convert 1,25 dihydroxyvitamin D and 25-hydroxyvitamin D to their inactive metabolites[1]. 24-hydroxylase deficiency due to CYP24A1 variants is rare and clinical presentation is characterized by hypercalcemia, nephrolithiasis and nephrocalcinosis. Treatment may include thiazide diuretics, sodium cellulose phosphate and ketoconazole.[1] We present a case of hypercalcemia due to 24-hydroxylase deficiency. Clinical Case: A 56-year-old male with chronic kidney disease initially presented with hypercalcemia at age 48 to another institution. He was initially diagnosed with primary hyperparathyroidism in the setting of an inappropriately normal parathyroid hormone (PTH) with hypercalcemia. He subsequently had one parathyroid gland removed a year after diagnosis, then another two years later due to continued hypercalcemia. However, he continued to have persistent hypercalcemia, 10.9-12.7 mg/dL but now in the setting of low PTH. In addition, his 1,25 dihydroxyvitamin D was high normal and 25-hydroxyvitamin D was high off exogenous vitamin D supplementation, which raised the suspicion for 24-hydroxylase deficiency. He presented to our institution eight years later. Initial evaluation revealed, calcium 12.4 (8.6-10.5 mg/dL), phosphorous 2.9 (2.5-4.5 mg/dL), normal albumin, PTH 13 (15-65 pg/mL), 1,25 dihydroxyvitamin D 87.2 (19-79.3 pg/mL) and 25-hydroxyvitamin D 38.3 (20-50 ng/mL), 24hr urine calcium 0.23 (0.05-0.30 g/24hr), fractional excretion calcium 0.02. His 25-hydroxyvitamin D:24,25 dihydroxy vitamin D ratio was unable to be calculated, since 24,25 dihydroxy vitamin D was below the limit of quantification. He also had evidence of nephrocalcinosis on renal ultrasound. Evaluation of other causes of non-PTH mediated hypercalcemia included normal angio converting enzyme, PTHrP level, vitamin A level, SPEP and UPEP. Chest X-ray did not demonstrate any evidence of granulomatous disease. He has been managed conservatively for suspected 24-hydroxylase deficiency. He has been advised to limit calcium and vitamin D intake, as well as sun exposure, with close monitoring of his calcium levels. His calcium levels have ranged from 10.7-12.4 mg/dL and he has had one hospitalization in the setting of heart failure where his calcium levels improved with furosemide to 8.7-9.9 mg/dL. Conclusion: In patients with persistent non-PTH dependent hypercalcemia, 24-hydroxylase deficiency should be a differential diagnosis when other common causes are excluded.

THU280 Acute Interstitial Nephritis- A Complication Of Semaglutide Use

Abstract Disclosure: M. Alsayed Hasan: None. J. Doroshow: None. Background: With the widespread use of glucagon-like peptide 1 (GLP-1) agonists in diabetes, several cases have been reported of GLP-1 induced acute interstitial nephritis (AIN) with variable recovery in kidney function (1). Although it is a rare side effect, the primary management requires early identification and removal of the offending agent. Clinical Case: A 75-year-old male presented with a week of nausea, vomiting, abdominal pain, and reduced urine output. He was started on semaglutide 4 months prior to admission when his creatinine was 1.16 mg/dL. Initial lab abnormalities included an elevated blood urea nitrogen 119 mg/dL (n 8-20 mg/dL), elevated creatinine 13.8 mg/dL (n 0.7-1.3 mg/dL), anion gap acidosis with a CO2 of 15 mEq/L (n 22-32 mEq/L) and an anion gap of 18 (n&amp;lt;12), lipase 659 U/L (n 20-51 U/L). His urinalysis demonstrated too numerous to count red blood cells, 4-10 white blood cells, rare eosinophils and no casts or crystals. Urine culture was negative. The fractional excretion of sodium and urea were 5.56% and 56% respectively, consistent with intrinsic renal disease. CT of the abdomen and pelvis demonstrated peri-pancreatic inflammation. A follow up renal ultrasound showed normal echotexture with no hydronephrosis or renal calculi. His picture was concerning for pancreatitis and pre-renal/acute tubular necrosis from diuretic use and vomiting. Despite aggressive fluid resuscitation, there was minimal improvement in his creatinine. Further work up for his renal injury was negative for monoclonal antibodies on protein electrophoresis and immunofixation. An autoimmune work up was negative for antinuclear antibody, anti-double stranded DNA, antineutrophil cytoplasmic (ANCA) myeloperoxidase IgG, anti-proteinase 3 ANCA IgG, glomerular basement membrane antibody, hepatitis B and C antibodies, and HIV. Complements and immunoglobin G subclasses were normal. A renal biopsy was performed which showed active interstitial inflammation with eosinophils consistent with allergic interstitial nephritis without an immune complex mediated glomerular lesion. He was started on intravenous methyl prednisone for 3 days followed by a prednisone taper. His home metformin, ramipril and hydrochlorothiazide were discontinued on discharge. He was eventually started on mycophenolate as the creatinine did not return to baseline with steroids. Conclusion: AIN is a rare, yet serious complication of GLP-1 use that requires early identification and discontinuation of the medication. A rapid or unexplained decline in renal function after starting a GLP-1 should be evaluated early on with concern for AIN once volume depletion is ruled out (1). Reference: (1) Chaudhury N., Liarakos A., Gopalakrishnan K., Ayub W., Murthy N., Rao R. Antidiabetic medication-induced acute interstitial nephritis: case report and literature search. British Journal of Diabetes. 2021;21(2);228-32. Presentation: Thursday, June 15, 2023

THU236 Mild Asymptomatic Hypercalcemia Secondary To A Novel Calcium-sensing Receptor Mutation

Abstract Disclosure: J. Tarkoff: None. Background: Familial hypocalciuric hypercalcemia (FHH) is a rare cause of mild hypercalcemia that is usually secondary to heterozygous mutations of the calcium-sensing receptor (CaSR) with autosomal dominant inheritance. The distinction between this entity and primary hyperparathyroidism can be difficult. Clinical Case: A 15-year-old female presented to the endocrinology clinic for an incidentally found elevated total calcium of 10.9 mg/dl (8.9-10.4) and elevated ionized calcium 5.5 mg/dl (4.8-5.3 mg/dl). Her labs at that time also showed a PTH of 29 pg/mL (12-71) and phosphorus 3.5 mg/dl (2.5-4.5 mg/dl). She denied any symptoms of hypercalcemia and there is no reported family history of mineral disorders or fractures. She does not take any medications. Her physical exam was unremarkable. Our evaluation showed calcium 10.5 mg/dl, phosphorus 4 mg/dl, magnesium 2.2 mg/dl (1.5-2.5 mg/dl) 25-hydroxyvitamin D 32 ng/ml (30-100 ng/ml), fractional excretion of calcium (FeCa) based upon spot urine sample = 0.0104, TSH 1.29 mIU/L (0.5-4.3 mIU/L), alkaline phosphatase 79 U/L (45-150 U/L), and normal renal function. Given her spot FeCa being &amp;lt;0.02, sequencing of the CASR gene was offered to the family because of potential overlap of her FeCa with primary hyperparathyroidism for which the treatment would be surgical (1). Commercial genetic testing was notable for a previously unreported heterozygous nonsense mutation, c.3001C&amp;gt;T (p.Gln1001X). It is expected to disrupt the final 78 amino acids of the protein in its intracellular domain and may play a role in preventing downstream signaling. At follow-up without treatment, her calcium has ranged between 10-10.9 mg/dl and she remains asymptomatic. Clinical lesson/conclusion: Hypocalciuria in the setting of hypercalcemia should raise the suspicion of FHH even without family history. Genetic testing of the CaSR is a crucial step in facilitating the diagnosis of FHH, especially given the importance of distinguishing it from primary hyperparathyroidism. Reference: (1) Christensen, S.E., Nissen, P.H., Vestergaard, P., Heickendorff, L., Brixen, K. and Mosekilde, L. (2008), Discriminative power of three indices of renal calcium excretion for the distinction between familial hypocalciuric hypercalcemia and primary hyperparathyroidism: a follow-up study on methods. Clinical Endocrinology, 69: 713-720. Presentation: Thursday, June 15, 2023