Population-based Reference Intervals Research Articles

Defining Gestational Thyroid Dysfunction Through Modified Nonpregnancy Reference Intervals: An Individual Participant Meta-analysis.

Establishing local trimester-specific reference intervals for gestational TSH and free T4 (FT4) is often not feasible, necessitating alternative strategies. We aimed to systematically quantify the diagnostic performance of standardized modifications of center-specific nonpregnancy reference intervals as compared to trimester-specific reference intervals. We included prospective cohorts participating in the Consortium on Thyroid and Pregnancy. After relevant exclusions, reference intervals were calculated per cohort in thyroperoxidase antibody-negative women. Modifications to the nonpregnancy reference intervals included an absolute modification (per .1 mU/L TSH or 1 pmol/L free T4), relative modification (in steps of 5%) and fixed limits (upper TSH limit between 3.0 and 4.5 mU/L and lower FT4 limit 5-15 pmol/L). We compared (sub)clinical hypothyroidism prevalence, sensitivity, and positive predictive value (PPV) of these methodologies with population-based trimester-specific reference intervals. The final study population comprised 52 496 participants in 18 cohorts. Optimal modifications of standard reference intervals to diagnose gestational overt hypothyroidism were -5% for the upper limit of TSH and +5% for the lower limit of FT4 (sensitivity, .70, CI, 0.47-0.86; PPV, 0.64, CI, 0.54-0.74). For subclinical hypothyroidism, these were -20% for the upper limit of TSH and -15% for the lower limit of FT4 (sensitivity, 0.91; CI, 0.67-0.98; PPV, 0.71, CI, 0.58-0.80). Absolute and fixed modifications yielded similar results. CIs were wide, limiting generalizability. We could not identify modifications of nonpregnancy TSH and FT4 reference intervals that would enable centers to adequately approximate trimester-specific reference intervals. Future efforts should be turned toward studying the meaningfulness of trimester-specific reference intervals and risk-based decision limits.

A-108 Re-evaluation of reference intervals for circulating albumin, total calcium, and magnesium levels among subjects in Dallas County

Abstract Background Reference intervals are either directly established from normal volunteers, adopted from assay manufactures and verified as transferable to the normal population, or indirectly derived using patients’ archived laboratory data. This study describes indirect derivation of reference intervals for albumin, total calcium, and magnesium appropriate to the patient population of Dallas County. The tests were selected due to their often combine measurement in the assessment of calcium and bone mineral metabolism Methods Retrospective reported laboratory results during May 2022 for albumin (n=1342), total calcium (n=1945), and magnesium (n=2148) were obtained. Values were subjected to statistical analysis for nature of distribution, mean, and standard deviation as well as stratified for patients’ characteristics (gender, race, and age). Statistical analysis applied were Hoffman regression analysis, one-way ANOVA, and Tukey-Kramer tests. Results Following removal of outliers, statistically suggested reference intervals for albumin, total calcium, and magnesium were 5.5 to 2.4 g/dL, 10.5 to 7.5 mg/dL, and 2.6 to 1.6 mg/dL respectively. Although there was race specific differences in albumin and calcium levels (p=0.032) and (p=0.002) respectively, differences for magnesium were slightly nonsignificant (p=0.06). Similarly, significant differences due to age were observed for albumin, total calcium, and magnesium (P <0.00 for all). The data suggests that albumin, magnesium, and calcium levels are unequivocally dependent on age and race for patients in Dallas County. The upper limits of population derived, and manufacturer verified reference intervals were 5.45 and 5.2 g/dL for albumin, 10.5 and 10.2 mg/dL for calcium, and 4.6, and 2.6 mg/dL for magnesium respectively, the lower limits were 2.4 and 3.5, 7.5 and 8.4, 1.4, and 1.6 mg/dL respectively. Conclusions Reference intervals for albumin, total calcium, and magnesium appropriate to the patient population of Dallas County were derived. Derived values were statistically different from the manufacturer verified values in use. The study although limited by the small number of acceptable samples, highlights the need for laboratories to derive their respective population-based reference intervals. The study will be expanded to other biochemical parameters utilizing much larger sample volume.

Population-based anti-Müllerian hormone reference intervals help define gonadal status in the bitch.

To establish statistically valid, population-based reference intervals (RIs) for canine anti-Müllerian hormone (AMH) and define changes in AMH and inhibin-B in bitches during breeding cycles. A homologous canine ELISA was used to measure AMH in serum samples (collected between May 2019 and July 2024) from 102 intact and 78 reportedly ovariohysterectomized (OVH) bitches and 8 bitches before and after ovariohysterectomy, and in longitudinal samples from 24 bitches undergoing breeding management. Established 95% RIs were used in a retrospective assessment of 3,193 clinical submissions. Cyclic variation of AMH and inhibin-B (heterologous ELISA) were regressed with time and normalized to the rise in progesterone in samples from breeding bitches. Intact and OVH RIs for AMH were calculated with and without inclusion of 7 samples from reportedly OVH bitches that had AMH concentrations in the intact RI. Anti-Müllerian hormone and inhibin-B were positively correlated, and AMH was 3 times higher in proestrus than in estrus. Retrospectively, of 3,193 samples submitted for clinical AMH testing, 41% to 56% were in or above the intact AMH interval, 37% to 44% were within the OVH interval, and < 10% were inconclusive, depending on how RIs were defined. Statistically valid, population-based RIs establish a sound basis for interpreting results of clinical submissions requesting AMH to assess gonadal status in the bitch. Confirmation of cyclic variation in AMH (and, for the first time, inhibin-B) reaffirms proestrus as the optimum time to draw samples, and ≤ 10% of samples submitted for determination of gonadal status are expected to fall in an inconclusive AMH RI.

Reference Intervals Revisited: A Novel Model for Population-Based Reference Intervals, Using a Small Sample Size and Biological Variation Data.

Conventional population-based reference intervals (popRIs) are established on the ranking of single measurement results from at least 120 reference individuals. In this study, we aimed to explore a new model for popRIs, utilizing biological variation (BV) data to define the reference interval (RI) limits and compared BV-based popRI from different sample sizes with previously published conventional popRIs from the same population. The model is based on defining the population set point (PSP) from single-measurement results of a group of reference individuals and using the total variation around the PSP, derived from the combination of BV and analytical variation, to define the RI limits. Using data from 143 reference individuals for 48 clinical chemistry and hematology measurands, BV-based popRIs were calculated for different sample sizes (n = 16, n = 30, and n = 120) and considered acceptable if they covered 90% of the population. In addition, simulation studies were performed to estimate the minimum number of required reference individuals. The median ratio of the BV-based to conventional RI ranges was 0.98. The BV-based popRIs calculated from the different samples were similar, and most met the coverage criterion. For 25 measurands ≤16 reference individuals and for 23 measurands >16 reference individuals were required to estimate the PSP. The BV-based popRI model delivered robust RIs for most of the included measurands. This new model requires a smaller group of reference individuals than the conventional popRI model and can be implemented if reliable BV data are available.

Towards Personalized TSH Reference Ranges: A Genetic and Population-Based Approach in Three Independent Cohorts.

Background: Serum thyroid-stimulating hormone (TSH) measurement is the diagnostic cornerstone for primary thyroid dysfunction. There is high inter-individual but limited intra-individual variation in TSH concentrations, largely due to genetic factors. The currently used wide population-based reference intervals may lead to inappropriate management decisions. Methods: A polygenic score (PGS) including 59 genetic variants was used to calculate genetically determined TSH reference ranges in a thyroid disease-free cohort (n = 6,834). Its effect on reclassification of diagnoses was investigated when compared to using population-based reference ranges. Next, results were validated in a second independent population-based thyroid disease-free cohort (n = 3,800). Potential clinical implications were assessed in a third independent population-based cohort including individuals without thyroid disease (n = 26,321) as well as individuals on levothyroxine (LT4) treatment (n = 1,132). Results: PGS was a much stronger predictor of individual TSH concentrations than FT4 (total variance in TSH concentrations explained 9.2-11.1% vs. 2.4-2.7%, respectively) or any other nongenetic factor (total variance in TSH concentrations explained 0.2-1.8%). Genetically determined TSH reference ranges differed significantly between PGS quartiles in all cohorts, while the differences in FT4 concentrations were absent or only minor. Up to 24.7-30.1% of individuals, previously classified as having subclinical hypo- and hyperthyroidism when using population-based TSH reference ranges, were reclassified as euthyroid when genetically determined TSH reference ranges were applied. Individuals in the higher PGS quartiles had a higher probability of being prescribed LT4 treatment compared to individuals from the lower PGS quartiles (3.3% in Q1 vs. 5.2% in Q4, Pfor trend =1.7 × 10-8). Conclusions: Individual genetic profiles have the potential to personalize TSH reference ranges, with large effects on reclassification of diagnosis and LT4 prescriptions. As the currently used PGS can only predict approximately 10% of inter-individual variation in TSH concentrations, it should be further improved when more genetic variants determining TSH concentrations are identified in future studies.

On-Field Rule Out of Mild Traumatic Brain Injury: Can Blood-Based Biomarker Testing Change Outcome of Major Sporting Events?

Mild traumatic brain injury (mTBI) is defined as a Glascow Coma Score of between 13 and 15. The diagnosis and rule out of individuals suffering from mTBI on an acute basis is imperfect and involves subjective measures. Serum biomarkers that exhibit narrow within-individual biological variation can be used for the early rule-out of mTBI, when baseline levels are compared during health. This is a descriptive study that applies published biological variation data of serum mTBI biomarkers for early rule out of sports-related injury. Laboratory tests such as glial fibrillary acidic protein, fatty acid binding protein 7, and phosphorylated protein enriched in astrocytes have low within-individual variances and are potential candidates. Aldolase C also rises early in blood but the biological variation is of this marker is currently unknown. The use of blood-based biomarkers, measured in real time using point-of-care testing devices when compared to a pre-competition baseline instead of a population-based reference interval, can provide early rule out of mTBI, and possibly enable on-field evaluations and a medical decision for a return to competition.

Gestational age-specific reference intervals for androgens in pregnancy.

Androgen could impact cervical remodelling during pregnancy, and a higher level is associated with adverse pregnancy outcomes. A population-based gestation age-specific reference interval (RI) of total testosterone (TT), androstenedione (A4), and 17-hydroxyprogesterone (17-OHP) can help to diagnose maternal hyperandrogenism. We enrolled 600 healthy Chinese women to obtain longitudinal serum samples across gestation. The serum androgen profile was measured by liquid chromatography-tandem mass spectrometry. The equations for medians of TT, A4, and 17-OHP were generated by MedCal, and the variances adjusted for 2-level modeling were generated by MLwiN, a system for the specification and analysis of a range of multilevel models. A4 and TT levels increased across the gestation, and they closely correlated with each other (R = 0.90, P=<0.001), whereas 17-OHP level decreased from 5th gestational week to 16th gestational week and then increased afterward towards the end of pregnancy. Women diagnosed with preeclampsia (PE) were found to have a significantly higher level of A4, TT, and 17-OHP when compared with non-PE cases with p ≤0.01, whereas mothers carrying male versus female fetuses have comparable levels of A4, TT, and 17-OHP. The study highlights a methodology for constructing gestational age-specific TT, A4, and 17-OHP levels to provide a better interpretation of results in a cohort of healthy Chinese women. The observation in PE supports previous findings, and the higher levels of TT, A4, and 17-OHP were observed before the onset of PE.

Biological variation of 16 biochemical analytes estimated from a large clinicopathologic database of dogs and cats.

Biochemical measurements are commonly evaluated using population-based reference intervals; however, there is a growing trend toward reassessing results with within-subject variation (CVI). We aimed to estimate the CVI of 16 biochemical analytes using a large database of dogs and cats, which refers to the results of routine health checkups. Pairs of sequential results for 16 analytes were extracted from a database of adult patients. The second result was divided by the first result to produce the ratio of sequential results (rr), and the frequency distribution of rr was plotted. From the plots, the coefficient of variation (CVrr) was calculated. Analytical variation (CVA) was calculated using quality control data, and CVI was estimated as follows: . Estimated CVI was compared with previously reported CVI using the Bland-Altman plot analysis. From the database, 9078 data points from 3610 dogs and 3743 data points from 1473 cats were extracted, with 5468 data pairs for dogs and 2270 for cats. Sampling intervals ranged from 10 to 1970 days (median 366) for dogs and 23 to 1862 days (median 365) for cats. Bland-Altman analysis showed most CVI plots fell within the limits of agreement; however, positive fixed biases were observed in both dogs and cats. Our study introduces a novel approach of estimating CVI using routine health checkup data in dogs and cats. Despite biases, our method holds promise for clinical application in assessing the significance of measurement result differences.

Specifications of qPCR based epigenetic immune cell quantification.

Immune monitoring is an important aspect indiagnostics and clinical trials for patients with compromised immune systems. Flow cytometry is the standard method forimmune cell counting but faces limitations. Bestpracticeguidelines are available, but lack of standardization complicates compliance with e.g., invitro diagnostic regulations. Limited sample availability forces immune monitoring to predominantly use population-based reference intervals. Epigenetic qPCR has evolved asalternative with broad applicability and low logistical demands. Analytical performance specifications (APS) havebeen defined for qPCR in several regulated fields including testing of genetically modified organisms or vector-shedding. APS were characterized using five epigenetic qPCR-based assays quantifying CD3+, CD4+, CD8+ T, B and NK cells in light of regulatory requirements. Epigenetic qPCR meets all specifications including bias, variability, linearity, ruggedness and sample stability as suggested by pertinent guidelines and regulations. The assays were subsequently applied to capillary blood from 25 normal donors over a 28-day period. Index of individuality (IoI) and reference change values were determined to evaluate potential diagnostic gains of individual reference intervals. Analysis of the IoI suggests benefits for individual over population-based references. Reference change values (RCVs) show that changes of approx. Fifty percent from prior measurement are suggestive for clinically relevant changes in any of the 5 cell types. The demonstrated precision, long-term stability and obtained RCVs render epigenetic cell counting a promising tool for immune monitoring in clinical trials and diagnosis.

Biological variation of plasma 25-Hydroxyvitamin D3, Serum vitamin B12, folate and ferritin in Turkish healthy subject

Biological variation (BV) plays a crucial role in determining analytical performance specifications, assessing serial measurements of individuals, and establishing the use of population-based reference intervals. Our study aimed to calculate the BV and BV-based quality goals of 25-hydroxyvitamin D3 (25-OH D3), ferritin, folate and vitamin B12 tests. We included a total of 22 apparently healthy volunteers (9 women and 13 men) aged 18-55 years in the study that we conducted in Turkey. Blood samples were collected from the participants once a week for five weeks. Serum ferritin, folate and vitamin B12 levels were measured using immunochemical method, while plasma 25-OH D3 levels were determined using the high-performance liquid chromatography method. Analysis of variance (ANOVA) was used to estimate analytical variation(CVA), within-subject BV(CVI) and between-subject BV(CVG). The individuality index (II) and reference change value (RCV) were calculated based on these data. The CVI of 25-OH D3, ferritin, folate, and vitamin B12 were found to be 1.8% (0.6%-2.5%), 16.9% (14.4%-20.2%), 10.7% (9.2%-12.7%), and 8.6% (6.8%-10.5%), respectively. CVG were 44.2% (34.3%-69.9%), 132% (87.7%-238%), 19.4% (14.4%-28.8%), and 39.6% (29.8%-59.0%) for the same biomarkers, while CVA were 3.2% (2.81%-3.71%), 3.5% (3.1%-4.1%), 4.0% (3.5%-4.6%), and 7.5% (6.6%-8.6%), respectively. The II values for 25-OH D3, ferritin, folate, and vitamin B12 were calculated as 0.04, 0.13, 0.55, and 0.22, respectively. The RCV were 10.2%, 47.8%, 31.7%, and 31.6%, respectively. Because the tests analyzed in this study exhibit high individuality, RCV should be preferred rather than population-based reference ranges in clinical interpretation of results.

Biological Variation in Biochemistry Analytes in Laboratory Guinea Pigs (Cavia porcellus).

Biological variation (BV) describes the physiological random fluctuation around a homeostatic set point, which is a characteristic of all blood measurands (analytes). That variation may impact the clinical relevance of the changes that are observed in the serial results for an individual. Biological variation is represented mathematically by the coefficient of variation (CV) and occurs within each individual (CVI) and between individuals in a population (CVG). Biological variation data can be used to assess whether population-based reference or subject-based reference intervals should be used for the interpretation of laboratory results through the calculation of the index of individuality (IoI). This study aimed to determine the biological variations, calculate the IoI and reference change values (RCV) of clinical chemistry analytes in an outbred strain colony of Hartley guinea pigs (GPs), and set the quality specifications for clinical chemistry analytes. Blood was collected from 16 healthy adult laboratory colony GPs via jugular venipuncture at weekly intervals over six weeks. All the samples were frozen and analyzed in a single run. Analytical, CVI, and CVG biological variations, together with the IoI and RCV, were calculated for each measurand. Based on the estimated BV, the calculated IoI was low for glucose, so individual reference intervals (RCV) should be used. The majority of the measurands should be interpreted using both population-based and subject-based reference intervals as the IoIs were intermediate.

A-018 Biological Variation Estimates for N-terminal pro-B-type Natriuretic Peptide from Eight Healthy Turkish Women

Abstract Background B-type natriuretic peptide (BNP) and its precursor N-terminal pro-B-type natriuretic peptide (NT-proBNP) are released primarily by the ventricles in the heart in response to volume or pressure overload. Measurements of NT-proBNP are used as an aid in the diagnosis and assessment of severity of congestive heart failure (CHF). Within- (CVI) and between-subject (CVG) biological variation (BV) estimates for NT-proBNP are limited. Here biological variability (BV) estimates from eight apparently healthy Turkish women for NT-proBNP are provided. Methods Serum samples were collected weekly from 24 healthy subjects (12 male, 12 female) for 10 consecutive weeks and stored at −80 °C prior to analysis. Study participant samples were analyzed in duplicate within a single run using the Atellica® IM NT-proBNP (PBNP) assay* on the Atellica IM Analyzer. Outlier detection, variance homogeneity analyses, and trend analysis were performed followed by CV-ANOVA to determine BV and analytical variation (CVA) estimates with 95% CI. The asymmetrical reference change values (RCV) using the lognormal approach, index of individuality (II), and analytical performance specification (APS), based on the CVA estimate derived in our study, were also calculated. Results PBNP results from 11 males and 3 females were lower than the limit of quantitation (LoQ) of the assay (&amp;lt;35 pg/mL). The remaining male sample was not included in the analysis. One female sample was identified as an outlier between individuals and was excluded from the analysis. To fulfil criteria for variance homogeneity of the data from eight women, 7% of results were excluded. In total, 104 analytical results were included in the analysis. PBNP data for the female group was normally distributed, and no trends were identified by regression analysis. The BV estimates derived from females were CVI: 23.7%, (95% CI 19.0–30.4) and CVG: 8.22%, (95% CI 0.0–24.7). The CVA obtained from replicate test results was 11.2% (95% CI 9.4–13.9), which was lower than the desirable APS for imprecision. The II, calculated as the ratio of CVI/CVG, indicated a low individuality of PBNP (defined as II &amp;gt; 1.6). Thus, use of a population-based reference interval for interpreting serial PBNP measurements is more appropriate than use of the RCV. Conclusions This study provides updated BV estimates for NT-proBNP derived from a protocol consistent with European Federation of Clinical Chemistry and Laboratory Medicine recommendations. The availability of BV estimates allows for refined APS and associated II and RCV, which are applicable when using PBNP as an aid in the diagnosis and assessment of severity of congestive heart failure. *The products/features mentioned here are not commercially available in all countries. Their future availability cannot be guaranteed.

Personalized and Population-Based Reference Intervals for 48 Common Clinical Chemistry and Hematology Measurands: A Comparative Study.

Personalized reference intervals (prRIs) have the potential to improve individual patient follow-up as compared to population-based reference intervals (popRI). In this study, we estimated popRI and prRIs for 48 clinical chemistry and hematology measurands using samples from the same reference individuals and explored the effect of using group-based and individually based biological variation (BV) estimates to derive prRIs. 143 individuals (median age 28 years) were included in the study and had fasting blood samples collected once. From this population, 41 randomly selected subjects had samples collected weekly for 5 weeks. PopRIs were estimated according to Clinical Laboratory Standards Institute EP28 and within-subject BV (CVI) were estimated by CV-ANOVA. Data were assessed for trends and outliers prior to calculation of individual prRIs, based on estimates of (a) within-person BV (CVP), (b) CVI derived in this study, and (c) publically available CVI estimates. For most measurands, the individual prRI ranges were smaller than the popRI range, but overall about half the study participants had a prRI wider than the popRI for 5 or more out of 48 measurands. The dispersion of prRIs based on CVP was wider than that of prRIs based on CVI. The prRIs derived in our study varied significantly between different individuals, especially if based on CVP. Our results highlight the limitations of popRIs in interpreting test results of individual patients. If sufficient data from a steady-state situation are available, using prRI based on CVP estimates will provide a RI most specific for an individual patient.

The Diagnostic Utility of IgG Index and Oligoclonal Bands for Multiple Sclerosis in a Neurology Hospital Patient Population.

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system. Diagnosis is based on the 2017 revised McDonald criteria. Unmatched oligoclonal bands (OCB) within the CSF (i.e. positive OCB) can substitute for dissemination in time by magnetic resonance imaging. Simonsen et al (2020) claimed a raised (>0.7) immunoglobulin G (IgG) index could replace OCB status. This study aimed to establish the diagnostic utility of IgG index for MS in the population served by The Walton Centre NHS Foundation Trust(WCFT) a neurology and neurosurgery hospital, and to derive a population-based IgG index reference interval. OCB results from the laboratory information system were collated from November 2018-2021. Final diagnosis and medication history was obtained from the electronic patient record. Exclusions were made based on age (<18 years) at the time of lumbar puncture (LP) disease modifying treatment prior to LP, unknown IgG index and unclear OCB patterns. 935 of 1101 results remained following exclusions. 226 (24.2%) had a diagnosis of MS, 212 (93.8%) were OCB positive and 165 (73.0%) had a raised IgG index. The diagnostic specificity of a raised IgG index was calculated at 90.3% compared to 86.9% for positive OCB. 386 results with negative OCB were used to establish the IgG index reference interval (0.36-0.68) at 95th percentiles. This study provides evidence that IgG index should not replace OCB in the diagnosis of MS. >0.7 is an appropriate cut-off to define a raised IgG index for the patient population.

Assesing the effect of thyroid dysfunction during pregnancy on maternal and neonatal outcomes with guidelines and population-based gestation-specific reference intervals

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Evaluation of Biological Variation of Different Clinical Laboratory Analytes in the Blood of Healthy Subjects.

Background Biological variation (BV) as a prognostic marker implies that each individual has a "subject mean"or central tendency, control level, or "set point"concentration for maintaining homeostasis regulation, which is influenced by factors such as genes, diet, exercise, and age. Uses for information on BV include determining the value of population-based reference intervals, assessing the importance of variation in serial findings, and establishing criteria for judging correct analysis. Aims We focused on the assessment of BVparameters for these elements as within-subject BV (CVW), between subject BV (CVG), the index of individuality (II), and the reference change value (RCV) of important biochemical analytes in the Bangladeshi adult population. Methodology This is a cross-sectional analytical study of a representative sample in the population of Bangladesh to determine BV in clinical laboratory analytes. For the study, 758 people were requested to take part; among those 730 (ages 18-65) apparently, healthy adults were blood donors, hospital staff, laboratory personnel, or any individuals who presented themselves for health screening at a tertiary hospital in Dhaka, Bangladesh. Results The CVW for blood sugar, creatinine, urea, uric acid, sodium, potassium, chloride, calcium, magnesium, and phosphate were calculated as 5.10 %, 4.64%, 10.72%, 5.71%, 0.69%, 4.35%, 0.75%, 3.69%, 4.57%, and 4.72%, respectively. The CVG for blood sugar, creatinine, urea, uric acid, sodium, potassium, chloride, calcium, magnesium, and phosphate was 10.70%, 21.46%, 31.47%, 23.52%, 1.95%, 9.74%, 2.56%, 4.64%, 9.96 %, and 17.45%, respectively. The index of individuality (II) for blood sugar, creatinine, urea, uric acid, sodium, potassium, chloride, calcium, magnesium, and phosphate were 0.48, 0.22, 0.34, 0.24, 0.35, 0.45, 0.29, 0.79, 0.46, and 0.27, respectively. The RCVfor blood sugar, creatinine, urea, uric acid, sodium, potassium, chloride, calcium, magnesium, and phosphate was 14.75%, 14.10%, 30.58%, 16.13%, 2.82%, 12.58%, 3.54%, 10.62%, 13.62 %, and 15.80%, respectively. Conclusions Nine serum biochemistry analytes (blood sugar, creatinine, urea, uric acid, sodium, potassium, chloride, magnesium, and phosphate) had low individuality, indicating that subject-based reference intervals are appropriate, only one analyte (calcium) had high individuality and, therefore, population-based reference intervals are more appropriate.

Plasma procalcitonin kinetics in healthy dogs and dogs undergoing tibial plateau leveling osteotomy.

Procalcitonin (PCT) is a well-established biomarker for bacterial infection in human patients. We aimed to analyze the kinetics of plasma PCT (pPCT) in healthy dogs and dogs with canine cranial cruciate ligament (CCL) rupture undergoing tibial plateau leveling osteotomy (TPLO). This prospective, longitudinal study included 15 healthy dogs and 25 dogs undergoing TPLO. Hematology, pPCT, and C-reactive protein (CRP) were assessed on 3 consecutive days in healthy dogs and 1 day preoperatively and days 1, 2, 10, and 56 postoperatively. Inter- and intraindividual variability of pPCT were assessed in healthy dogs. Median pPCT concentrations of dogs with CCL rupture preoperatively were compared with healthy controls, and median pPCT concentrations, as well as percentage change postanesthesia, arthroscopy, and TPLO, were compared with baseline. For the correlation analysis, the Spearman rank correlation test was used. Inter- and intraindividual variabilities of pPCT in healthy dogs were 36% and 15%, respectively. Median baseline pPCT concentrations were not significantly different between healthy dogs (118.9pg/mL; IQR: 75.3-157.3pg/mL) and dogs undergoing TPLO (95.9pg/mL; IQR: 63.8-117.0pg/mL). Plasma PCT concentrations were significantly lower immediately post- than preoperatively (P < 0.001). CRP, WBC, and neutrophil concentrations increased significantly on post-OP day 2 and had normalized by day 10. These results indicate that CCL rupture, as well as anesthesia, arthroscopy, and TPLO combined, are not associated with increased pPCT concentrations in dogs with uncomplicated recovery. Considering the high intraindividual variability, individual serial measurements rather than a population-based reference interval should be considered.

Comparison of ionised calcium measured using a portable analyser to a reference method in healthy dogs.

To compare the ionised calcium measured on a portable analyser (iSTAT, Abbott) to a reference method. Blood samples from 39 apparently healthy dogs were analysed in duplicate using a portable analyser and a reference method (Radiometer ABL800 FLEX). Bland-Altman plots and Passing-Bablok regression were used to assess constant and proportional bias between the two instruments. A within-assay percentage coefficient of variation and total error (TE) was calculated for both analysers. The reference interval was calculated for the portable analyser using the robust method with confidence interval bootstrapping. The Bland-Altman plot showed a -0.036 mmol/L difference between the two instruments (95% confidence limit -0.08 to 0.01 mmol/L; limits of agreement -0.07 to 0.006 mmol/L). Neither the Bland-Altman plot nor the Passing-Bablock regression (slope -0.03; 95% confidence interval -0.08 to 0.19 and intercept 1; 95% confidence interval 0.83 to 1.2) showed significant proportional bias. The coefficient of variation for the portable analyser was 1.08%, compared to 0.78% for the reference method with a total error of 3.5% for the portable analyser. The estimated population-based reference interval for ionised calcium using the portable analyser is 1.23 to 1.42 mmol/L. For the healthy dogs in this study, compared to the reference method, the portable analyser showed no significant bias for measurement of ionised calcium. Further studies including hyper and hypocalcaemic dogs are required to determine clinical impact of the use of this analyser.

Biological Variations of Seven Clinical Chemistry Analytes and Trolox Equivalent Antioxidant Capacity within Salivary Constituents.

Data on biological variation in saliva samples are quite limited. This study aimed to obtain well-defined biological variation data for seven common clinical chemistry analytes and Trolox equivalent antioxidant capacity (TEAC) in saliva. Unstimulated whole saliva and blood samples were collected from thirty-two healthy volunteers of both genders without any history of disease or metabolic syndrome under standard conditions at six different times within three weeks. The seven clinical chemistry analytes and TEAC, analyzed by photometric methods using automated analyzers, were planned for biological variation analysis. The components of nested analysis of variance were used to perform the biological variation data analysis. The within-subject and between-subject biological variations (CVG and CVI, respectively) for unstimulated whole saliva samples, respectively, were determined to be 19.3% and 25.1% for α-amylase, 25.1% and 51.1% for aspartate aminotransferase, 31.0% and 22.3% for lactate dehydrogenase, 19.0% and 20.8% for uric acid, 16.6% and 23.4% for total calcium, 12.9% and 13.7% for inorganic phosphate, 13.1% and 19.7% for total protein, and 14.9% and 20.0% for TEAC. In addition, the CVI and CVG were 3.4% and 6.3% for serum TEAC. Considering the evidence that saliva samples can be used to diagnose and monitor oral or non-oral diseases, these biological variation data will contribute to how to use subject-based reference values or population-based reference intervals of these analytes and TEAC.

Biological variation of cardiovascular biochemical markers in patients with Type 2 Diabetes Mellitus

BackgroundType 2 diabetes mellitus (T2DM) is a well-established risk factor for cardiovascular diseases. We aimed to identify the biological variation of ten cardiovascular biochemical markers in T2DM patients to aid in their interpretation. MethodsBlood samples for evaluating ten biomarkers were collected biweekly from 23 T2DM patients (10 men, 13 women) for three months. The analytical variability and variations of within-subject (CVI) and between-subject (CVG) levels were calculated, as well as the analytical performance specifications, reference change value (RCV), and index of individuality (II). ResultsThe levels of total cholesterol (CHOL), apolipoprotein A (apoA), homocysteine (HCY), high-sensitivity troponin T (hsTnT) and N-terminal pro-brain natriuretic peptide (NT-proBNP) differed between males and females (P < 0.05). The CVIs or CVGs of the biomakers were higher than those of healthy participants in Westgard online database, except for hsTnT. Triglyceride (TG), lipoprotein (a) [Lp(a)] and NT-proBNP had relatively high CVI, CVG and RCV, whereas CHOL, high-density lipoprotein cholesterol (HDL-C), apoA and HCY showed low variation. Moreover, the II of HDL-C, LP(a), apoA, HCY and hsTnT was <0.6 and other biochemical markers was between 0.6 and 1.4. ConclusionThe cardiovascular biochemical markers in T2DM patients showed higher CVI or CVG, except for hsTnT. ApoA had the lowest CVI and CVG values. Population-based reference intervals should be used with caution in clinical decision-making for T2DM patients.