Accurate potassium measurements are clinically important because life-threatening arrhythmias can occur at high or low potassium levels. Even mild dyskalemia is associated with adverse clinical outcomes. However, preanalytical factors and varying specimen types-serum, plasma, and whole blood-pose challenges in accurately measuring potassium, establishing reference intervals (RIs), and interpreting the results. Adult RIs for potassium were acquired from 60 laboratory directories. The distribution of plasma potassium values at a cancer center and effects of applying different RIs were evaluated. Surveyed laboratories have 14 different RIs for serum potassium and, usually, the same RI for serum and plasma. Only 4 laboratories had different serum and plasma RIs. Applying common serum RIs to plasma measurements markedly affected the proportions of patient results outside the RI. Although potassium measurements are relatively well standardized, laboratory RIs for potassium vary considerably. Most laboratories use the same RI for serum and plasma potassium, although serum and plasma measurements usually differ by 0.2-0.4 mmol/L, exceeding acceptable limits for bias. Consequently, serum-derived RIs are suboptimal RIs for plasma. Testing of plasma specimens is common in acute care settings, but most laboratory RIs and clinical guidelines are based on serum measurements. Outcome studies show that there is a narrow optimal range for potassium levels and that outcomes improve with careful management of potassium levels. Separate RIs and clinical guideline values for plasma and serum potassium offer better assessment of potassium levels.

Gas-exchange derived pulmonary capacitance (GXCAP) is a non-invasive index of pulmonary arterial capacitance obtainable from submaximal cardiopulmonary exercise testing (CPET), but reference intervals in older adults, a key target population, are lacking. A secondary analysis of an open-label clinical device trial, including 207 adults ≥ 60 years undergoing elective non-cardiac surgery was performed. Submaximal CPET with the Shape II system provided peak GXCAP, GXCAP-time slope, and GXCAP-VO2 slope. Sex-specific empirical 95% reference intervals (2.5th-97.5th percentiles) and indirect reference intervals were calculated using the refineR algorithm, which models the latent healthy subpopulation within routine data. Associations with age and sex were examined using correlation and group comparisons. The analytic cohort comprised 207 nonsmoking participants (119 males, 88 females). Males demonstrated higher peak GXCAP and steeper GXCAP-time and GXCAP-VO2 slopes than females. Age was modestly and inversely associated with peak GXCAP and GXCAP-time slope. Empirical reference intervals were wide and right-skewed, whereas refineR produced narrower, physiologically plausible intervals, for example, peak GXCAP 144.9-810.0 mL.mmHg (overall), with higher upper limits in males. In older adults undergoing preoperative evaluation, GXCAP metrics show clear sex differences. Indirect, refineR-based, reference intervals provide stable, clinically interpretable ranges that may enhance the use of GXCAP for noninvasively assessing pulmonary arterial capacitance in submaximal CPET. GXCAP derivatives (GXCAP-time slope and GXCAP-VO2 slope were introduced and may offer distinct advantages in submaximal cardiopulmonary exercise testing. NCT05743673, Principal Investigator: Zyad J. Carr, M.D.

Defining age partitions for thyrotropin (TSH) reference intervals in infancy: a robust statistical approach.

The Total Thrombus-formation Analysis System 01 (T-TAS 01) is an advanced microchip-based device that enables quantitative assessment of blood thrombogenicity. However, broader clinical implementation remains limited by the lack of well-established reference intervals (RIs) in healthy, antithrombotic drug-naïve individuals. This study aimed to define RIs and identify clinical determinants of blood thrombogenicity in antithrombotic drug-naïve adults using T-TAS 01. Blood thrombogenicity was measured using T-TAS 01 in 319 adults without antithrombotic therapy who underwent health checkups at the Miyakonojo Health Service Center. The T-TAS 01 parameters, PL18-AUC10 and AR10-AUC30, were calculated as the areas under the flow-pressure curves of the PL-chip (type I collagen-coated) and the AR-chip (type I collagen and tissue factor-coated), respectively. Their associations with clinical parameters were assessed using multivariate regression analysis. The median age was 46.0 years; 64.3% of participants were female, and 82.1% had no hypertension, dyslipidemia, or diabetes. The median platelet count was 247 × 109/L. The median PL18-AUC10 and AR10-AUC30 values were 392.3 and 1335.9, with RIs of 236.3 to 468.1 and 1010.0 to 1496.2, respectively. PL18-AUC10 was independently associated with white blood cell count (coefficient, 5.15; 95% CI, 0.88-9.41) and platelet count (0.36; 95% CI, 0.25-0.47), whereas AR10-AUC30 was independently associated with body mass index (4.06; 95% CI, 0.06-8.06), platelet count (0.79; 95% CI, 0.52-1.06), and γ-glutamyl transpeptidase (-0.54; 95% CI, -0.90 to -0.18). Our findings provide foundational reference data for the clinical application of T-TAS 01 and support its potential as a point-of-care tool for individualized assessment of thrombogenicity.

The first international clinical standards of care for the gender-diverse population were formulated in the late 1970s. In the last 15 years, multiple subspecialty societies within the United States have developed clinical care guidelines for those with gender dysphoria, including gender-affirming hormone therapy (GAHT) and surgical treatments. To date, there are no pathology- and laboratory medicine-specific recommendations in the United States for the gender-diverse population. This document outlines pathology- and laboratory medicine-specific recommendations for providing optimal care to the gender-diverse population, with a predominant focus on the adult population. The scope of this document focuses on the following 5 topics: (a) reference intervals and interpretation of laboratory tests impacted by use of GAHT (testosterone for transgender men; estradiol with or without antiandrogens for transgender women), focusing on those stably on GAHT for 6 months or longer; (b) transfusion medicine considerations for the gender-diverse patient population, (c) consideration of gender diversity in autopsy and death investigation, (d) interpretation of histology from tissues that are impacted by GAHT and surgical procedures; and (e) pathology and laboratory medicine informatics challenges and opportunities. A relatively small group of laboratory tests is significantly impacted by GAHT. The histology of some tissues shows changes attributable to GAHT or to nonhormonal medical procedures. Autopsy and transfusion medicine practices for the gender-diverse population currently lack standardization, although this is evolving. The landscape of pathology informatics related to gender diversity is complicated by varying electronic health record and laboratory informatics systems functionality.

Measurement of triiodothyronine (T3) levels is important for the laboratory diagnosis and management of certain cases of thyrotoxicosis and for identifying conditions involving altered peripheral conversion of thyroxine (T4) to T3. However, whether total T3 (TT3) or free T3 (FT3) should be measured remains unclear. In this study, we performed a retrospective analysis of the results from 605 blood samples from 465 patients, in which thyroid-stimulating hormone (TSH), free T4 (FT4), TT3, and FT3 levels were measured in parallel. All the parameters were quantified using a widely used, fully automated electrochemiluminescence immunoassay platform, and reference intervals were based on those provided by the diagnostic test manufacturer. Despite a strong correlation between the TT3 and FT3 values (T3T ≤ 200 ng/dL: b = 0.0020, 95% confidence interval [CI]: 0.0019-0.0021, r = 0.841; T3T > 200 ng/dL: b = 0.0054, 95% CI: 0.0044-0.0064, r = 0.855), among 41 patients with elevated T3 values, 13 showed elevation of either TT3 or FT3, with a mild discordance between these values. Analysis of these discordant cases revealed a predominant pattern in which the FT3 levels better reflect clinical features and TSH and FT4 results than TT3 levels. The TT3 and FT3 results were generally well correlated, with elevated FT3 demonstrating performance superior to that of elevated TT3. Future studies should validate these findings across diverse populations with specific reference intervals and multiple immunoassay platforms.

Reference intervals for calculated free testosterone (cFT) in healthy, nonobese men have been released, but have not been validated in men with erectile dysfunction (ED). To assess the clinical impact of new cFT reference intervals in men with new-onset ED. Data from 410 healthy, nonobese men were analyzed (2015-2023). cFT was assessed using Vermeulen's formula and compared to Jasuja etal.'s (2022) reference values, using the 2.5th percentile as a pathological threshold. At baseline, all patients completed the International Index of Erectile Function (IIEF) and Beck Depression Inventory (BDI). Descriptive statistics and linear regression analyses were applied. Median (IQR) age and total testosterone at presentation were 48 (38-59) years and 4.7 (3.3-6.1) ng/mL. Median IIEF-EF score was 18 (8-23), with 134 patients (32.8%) reporting severe ED. Percentiles of cFT in ED men were: 2.5th = 10, 10th = 50, 50th = 90, 90th = 150, and 97.5th = 227.5 pg/mL, compared to 66, 91, 141, 240, and 309 pg/mL in healthy controls. Seventy-four had cFT between 10 and 66 pg/mL, normal for ED distribution but pathological by healthy reference. This group was older (p<0.01), had lower IIEF-EF (p<0.001), and higher BDI (p<0.01) versus those with cFT >66 pg/mL, though other parameters were similar. Severe ED rates were 72.7%, 44.6%, and 28.7% in men with cFT <10, 10-66, and >66 pg/mL (p<0.01). At multivariable regression, cFT >66 pg/mL was linked to higher IIEF-EF (p = 0.02), while cFT >66 pg/mL (p = 0.03) and younger age (p = 0.01) were associated with lower BDI scores. Reference thresholds for cFT derived from healthy men identify, among men with ED, a subgroup showing a less favorable erectile and psychometric profile. These findings suggest that healthy-derived cFT reference values may provide clinically useful information in the assessment of men presenting with ED.

This study aimed to estimate the reference interval for soluble B cell maturation antigen (sBCMA) in adults from Southern India. A total of 84 participants were enrolled. The sBCMA levels were measured, and statistical analyses were performed to assess differences across gender, age, and the presence of comorbidities such as diabetes mellitus (DM), hypertension (HTN), dyslipidemia (DLP), and obesity. Reference intervals were determined using a nonparametric approach with 95% coverage. The median sBCMA level was 74 ng/ml, with a mean of 75.52 ± 12.99 ng/ml. No significant differences were observed in sBCMA levels across gender, age, or comorbidities (p > 0.05). The mean differences between subgroups were below 13 ng/ml (25% of 52 ng/ml), indicating that partitioning reference ranges by subgroups was not required. The suggested reference interval for sBCMA in the study population is 54.75-106.75 ng/ml at 95% coverage. The suggested reference interval for our population is notably higher than that reported for the Caucasian population. Multiple reasons can account for this difference, including ethnic and genetic variation, environmental exposure, nutritional factors, analytical variation, and population characteristics. This study provides a population-specific reference interval for sBCMA in South Indian adults. Given the significant difference from Caucasian reference values, further research is needed to explore the underlying causes of this variation. The online version contains supplementary material available at 10.1007/s12288-025-02130-8.

To evaluate how alternative age-partitioning strategies affect result classification using discrete pediatric ferritin reference intervals (RIs). In a prospective cohort of 3,322 apparently healthy individuals aged birth to <19 years, serum ferritin was measured on the Cobas Pro platform. A common preprocessing pipeline, including Horn's algorithm, was applied once before all comparisons. Five age-partitioning schemes were evaluated: a data-driven classification and regression tree (CART)-based scheme (Scheme 1, reference), a physiology-informed high-resolution scheme, a CLSI-informed scheme, and two progressively broader pragmatic schemes. Nonparametric RIs were derived, and classification performance was assessed using apparent and out-of-bag (OOB) flagging rates, age-resolved analyses, discordance relative to Scheme 1, and boundary-focused and Lahti's evaluations. Overall flagging rates were similar across schemes (5.06-5.33 % apparent; 5.23-5.80 % OOB). However, substantial age-specific differences were observed. Discordance relative to Scheme 1 was lowest for Scheme 3 (1.99 %) and similarly low for Scheme 2 (2.26 %), but increased for Schemes 4 and 5 (3.76-4.64 %). Boundary discordance reached 15.0 % at 6months in broader schemes and reached 11.84 % at adolescent transitions. Age-resolved analyses showed marked heterogeneity during infancy, with overall flagging rates varying up to threefold between schemes within adjacent monthly bins. Lahti's evaluation confirmed non-interchangeability of adjacent partitions, particularly in early infancy. Despite similar overall flagging rates, marked age-specific classification differences occur, particularly in early infancy and around key developmental boundaries. Broader partitions may obscure physiological variation and increase classification discordance. Age-resolved evaluation should complement statistical criteria when defining pediatricRIs.

Breed-specific reference intervals for the Schirmer tear test (STT) and intraocular pressure (IOP) in Hamdani crossbred sheep have not been established. To determine reference intervals for STT and IOP in healthy Hamdani crossbred sheep. A total of 200 clinically healthy animals were stratified into four age groups: < 6 months, 6 months to 1 year, 1-2 years, and > 2 years. Each group comprised equal numbers of males (n = 25) and females (n = 25). Tear production was evaluated using STT-1, and IOP was measured with a rebound tonometer. Group-based mean values were calculated using representative values obtained by averaging measurements from both eyes. Mean values and reference intervals for STT and IOP were established for each age group. No sex-related differences were observed in STT values. However, age-related differences were observed only in females, with higher STT values in hoggets than lambs (p < 0.01). For IOP, ewes had higher values than rams (p < 0.01). Age-related differences in IOP were observed only in males, with rams showing lower IOP values than suckling lambs and hoggets (p < 0.01). This study establishes reference intervals for STT and IOP in healthy Hamdani crossbred sheep and provides clinically relevant baseline data for ophthalmic assessment.

Resistance to thyroid hormone alpha (RTHα) is a rare genetic disorder with symptoms of hypothyroidism, but normal or close-to-normal thyroid function tests. Treatment with levothyroxine (L-T4) may be beneficial. This study investigated the efficacy, safety and biochemical changes of high-dose L-T4 and liothyronine (L-T3) treatment. Four RTHα (Ala263Val) patients were treated with L-T4 (1.75 µg/kg) in a pilot open-label study and monitored for three years. Quality of life (QoL) was assessed using ThyPro. Analysis of auxiological- and biochemical-parameters, bone mineral density (BMD) and exploratory metabolomics was performed. A partial replacement of L-T4 with L-T3 was attempted. Treatment with L-T4 increased FT4, FT3, and rT3 to supraphysiological concentrations (relative to reference intervals) and suppressed thyroid-stimulating hormone with no adverse effects. Heart rate, bone markers, and sex hormone-binding globulin transiently increased. Several classes of lipids were reduced. BMD appeared unaltered. Patients reported improved QoL. One patient presented a short non-sustained ventricular tachycardia on L-T3 + L-T4. L-T4 treatment of adult RTHα patients was safe and improved QoL in adherent patients.

Transference of diagnostic thresholds for equine plasma ACTH from the Immulite 1000 to Immulite 2000XPi and Tosoh AIA systems.

A DEQAS review of the current performance of assays for the measurement of 1,25dihydroxyvitamin D.

Longitudinal assessment of hemostatic adaptations in pregnant mares: Evidence of a physiological hypercoagulable state.

Chronic kidney disease (CKD) in children exposes the developing brain to uremic and vascular insults, yet blood-based markers of the pediatric kidney-brain axis remain underexplored. We characterized neuron-specific enolase (NSE) and brain-derived neurotrophic factor (BDNF) across the spectrum of pediatric kidney disease. Prospective cohort of 75 children with measured GFR: 12 comparators with normal kidney function, 31 with non-dialysis CKD stages G2-G5, and 32 kidney transplant recipients (KTx). Biomarkers were measured by ELISA at baseline and after 3.2years. Cross-sectional and longitudinal analyses adjusted for age and group. NSE correlated inversely with age (r = - 0.46, p < 0.001) and did not differ between groups after age adjustment. NSE-age slopes were comparable in comparators and CKD but flat in transplanted children, indicating loss of the developmental decline in this group. BDNF correlated positively with measured GFR (r = 0.31, p = 0.018) and was lower in CKD than in comparators, consistent with reduced neurotrophic reserve in pediatric uremia. Circulating NSE in childhood reflects developmental stage rather than CKD status. Group comparisons in pediatric biomarker studies require age adjustment. Transplantation alters the NSE-age relationship beyond what kidney function explains. BDNF tracks kidney function in pediatric CKD. Age-stratified reference intervals are required before either marker can guide clinical decisions.

Reference intervals and variability of urinary traits in lactating Holstein cows.

Clinicians rely on reference intervals (RIs) to interpret laboratory test results. In pediatric populations, estimating RIs typically requires partitioning data by age, sex, and other relevant factors, which can lead to limited sample size and imprecise estimates; these limitations are addressed by using curve estimation, modeling hemoglobin level as a continuous function of age. To establish hemoglobin reference curves (RCs) for children and to complement recently published World Health Organization (WHO) thresholds by estimating hemoglobin optimal curves (OCs) that may inform more appropriate reporting standards. This cross-sectional study included healthy Canadian children aged 2 weeks through 10 years attending scheduled primary care visits from June 3, 2008, to February 26, 2020, in Toronto, Ontario, Canada. Data were analyzed from October 16, 2024, to February 1, 2026. Blood samples were collected and analyzed for hemoglobin, ferritin, and C-reactive protein levels. Parents completed a questionnaire to collect variables used as optimality criteria. Sex-specific RCs and OCs were estimated using nonparametric quantile regression with restricted cubic splines. RCs were based on the full sample, whereas OCs excluded children with indicators of suboptimal iron status. A web-based platform was developed to visualize these curves and calculate sex-specific reference and optimal limits by age. Findings were examined in relation to WHO hemoglobin thresholds. Blood samples from 4597 children (2451 males [53%]; median age, 38 months [IQR, 18-63 months]) were used to estimate hemoglobin RCs, and samples from a subgroup of 3426 children (1798 males [52%]; median age, 45 months [IQR, 24-68 months]) were used to estimate OCs. For females, lower OC hemoglobin limits were slightly below the lower RC limits up until age 2 years and became higher after age 6 years (eg, at 6 months, the OC lower limit was 9.91 g/dL [90% CI, 9.70-10.13 g/dL] vs 10.00 g/dL [90% CI, 9.78-10.23 g/dL] for RC). For males, lower OC limits were higher than lower RC limits until age 20 months (eg, at 6 months, the OC lower limit was 9.74 g/dL [90% CI, 9.46-10.02 g/dL] vs 9.28 g/dL [90% CI, 8.94-9.63 g/dL] for RC) and were similar afterwards. Differences in the upper limits were minimal for both sexes. WHO hemoglobin thresholds were consistently higher than lower limits of OCs across all ages but exceeded the 5th percentile curve only among children aged 5 through 10 years for both sexes (eg, for males aged 1 year, the OC lower limit was 10.06 g/dL [90% CI, 9.92-10.21 g/dL] vs the 10.5 g/dL WHO threshold). This cross-sectional study estimated sex-specific pediatric RCs for hemoglobin, modeled as a continuous function of age, to eliminate the need for age partitioning and overcome the associated sample size limitations. OCs, developed using health-based criteria, offered additional clinical context beyond traditional RIs. The findings highlight potential misalignments with existing WHO thresholds, particularly at younger ages.

Protein-bound uremic toxins (PBUTs), including indoxyl sulfate (IxS), p-cresol sulfate (pCS), indole-3-acetic acid (IAA), and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF), accumulate in patients with End-Stage Kidney Disease (ESKD) due to their resistance to conventional dialysis clearance and have been implicated in cardiovascular complications, oxidative stress, and disease progression. Accurate quantification of both total and free fractions of these toxins is essential for understanding their clinical significance, yet validated methods with population-specific reference intervals remain scarce. In this study, a rapid, sensitive, and fully validated LC-MS/MS method was developed for the simultaneous quantification of total and free serum concentrations of four PBUTs using a 4-minute chromatographic run and a single-step protein precipitation with an acetonitrile/acetone (1:1, v/v) solvent system. For the first time, indole-3-carboxylic acid was employed as an internal standard for IAA and CMPF quantification, while dihydrochlorothiazide (DHCT) was used for IxS and pCS. Method validation was performed in accordance with European Medicine Agency (EMA) guidelines, demonstrating excellent linearity (R² > 0.99), recovery (90-110%), minimal matrix effects (95-105%), and intra- and inter-day precision below 10% coefficient of variation (CV) for all analytes. Reference intervals for total PBUT concentrations were established using data from 120 healthy volunteers from a Turkish population cohort, representing the largest reference dataset reported to date for these analytes. The validated method was applied to serum samples from 118 maintenance hemodialysis patients, revealing significantly elevated total PBUT concentrations compared to healthy controls (p < 0.001 for all analytes), with IxS and pCS showing the most pronounced accumulation (approximately 29- and 23-fold higher, respectively). ROC curve analysis demonstrated excellent diagnostic performance for IxS (AUC = 0.986), pCS (AUC = 0.980), and CMPF (AUC = 0.943) in discriminating hemodialysis patients from healthy controls, while IAA showed limited discriminatory ability (AUC = 0.633), likely reflecting its distinct protein binding dynamics in uremic conditions. Spearman correlation analysis revealed significant associations between total PBUT levels and biochemical markers of renal function, further supporting the clinical relevance of the developed method. This validated LC-MS/MS approach offers a practical and reliable tool for simultaneous PBUT monitoring in clinical and research settings.

Intrahepatic cholestasis of pregnancy (ICP) requires timely diagnosis to guide management, including initiation of ursodeoxycholic acid (UDCA) and delivery planning. LC-MS/MS provides fractionated bile acid profiles but has a turnaround time (TAT) of approximately 1 week, delaying treatment. Enzymatic total bile acid (TBA) assays offer faster results but measure all bile acids collectively, which some have reported can be impacted by UDCA treatment. We validated the Diazyme enzymatic TBA assay on a Roche Cobas analyzer, assessing analytical measurement range, reference interval, precision, and accuracy vs LC-MS/MS. The comparison cohort included samples from 100 pregnant patients (median age 31 years; gestational age 34 weeks) presenting with pruritus and suspected of ICP. A secondary analysis examined UDCA and tauroursodeoxycholic acid in a UDCA-detectable subset. TAT was evaluated retrospectively in 971 specimens. We verified the assay's analytical measurement range of 1 to 180 µmol/L and reference interval of <10 µmol/L. Precision was <10%, and method comparison revealed minimal bias, with 98% clinical concordance. In the UDCA subset (n = 19), UDCA and tauroursodeoxycholic acid represented minor fractions of total TBA. Operationally, the enzymatic assay provided rapid results, with a median TAT of 5.6 h from collection (range 0.6-36.8) and 0.5 h from receipt (range 0.2-22.3); delays were mainly due to transport. The Diazyme enzymatic TBA assay on Roche Cobas demonstrates robust performance and rapid turnaround, supporting timely ICP diagnosis and management. LC-MS/MS remains useful for fractionated profiling but is limited by longer TAT.

ABSTRACT Background Owl monkeys ( Aotus spp.) are a nocturnal nonhuman primate (NHP) native to central and South America that are used as infectious disease research models for human diseases, such as malaria and human immunodeficiency virus. Natural and infectious diseases may cause alterations in the hematology and serum biochemistry values, which necessitate the availability of reliable reference intervals for healthy animals. Methods In this study, hematology and serum chemistry reference intervals for Aotus nancymae were calculated from 191 healthy animals (95 female, 96 male) and were generated based on age class (juvenile, adult, geriatric), sex (adults only), and across the entire sample. Results Significant differences were observed in multiple parameters as a function of sex and age, some of which are inconsistent with existing data from Aotus spp. and other NHPs. Conclusions The availability of age and sex specific reference intervals will be a valuable resource for monitoring the clinical health and effects of research interventions in owl monkeys.