Inter-method variability in bone alkaline phosphatase measurement: clinical impact on the management of dialysis patients

BACKGROUND

Bone-specific alkaline phosphatase (BAP) is now recommended to assess bone turnover in hemodialysis (HD) patients. However, little is known about potential variability between methods available to measure BAP.

METHODS

We measured BAP in 76 HD patients with six different assays (Beckman-Coulter Ostase IRMA, Beckman-Coulter Ostase Access, IDS iSYS Ostase, IDS Ostase enzyme immunoassay, DiaSorin Liaison Ostase and Quidel MicroVue BAP).

RESULTS

We observed a high correlation between all the assays ranging from 0.9948 (IDS iSYS vs. IDS EIA) to 0.9215 (DiaSorin Liaison vs. Quidel MicroVue). However, using the regression equations, the equivalent concentration of a Beckman-Coulter Access value of 10 μg/L can range from 7.7 to 14.4 μg/L and of 20 μg/L can range from 16.9 to 27.9 μg/L with other assays. According to Beckman-Coulter Access, 13%, 50% and 37% of the patients presented BAP values ≤10, between 10 and 20 and ≥20 μg/L, respectively. Discrepancies are observed when other assays are used (concordance from 10 to 100%).

CONCLUSIONS

Analytical problems leading to inter-method variation should be overcome to improve the usefulness of this marker in clinical practice. According to correlation results, recalibration of BAP assays is necessary but should not be a major issue.

Analytical and biological variation in repeated sweat chloride concentrations in clinical trials for CFTR modulator therapy

BACKGROUND

Using sweat chloride as a biomarker for CFTR modifying drugs requires knowledge of analytical and biological variation.

METHODS

979 sweat chloride concentrations from 128 subjects enrolled in the placebo arm of 2 multicenter, investigational drug trials were analyzed to determine coefficients of variation (CV) as well as reference change value (RCV) and index of individuality (II).

RESULTS

For these populations, calculated values for the two studies were: analytical variation (3.9, 4.1%); within-subject variation (4.4, 6.0%); between-subject variation (8.9, 7.0%); RCV (13.7, 17.0%) and II (0.7, 1.0). Sweat chloride variation was not affected by sex, collection site or sample weight; but was slightly affected by age in one of the two studies.

CONCLUSION

Through determination of analytical as well as between- and within-subject variation, and with a larger sample size, our data allows improved estimates of the RCV and II, and can contribute to future trials of CFTR modulators and inform the design and interpretation of n of 1 trials in both research and clinical settings.

Analytical and biological variability in biomarker measurement in the Hispanic Community Health Study/Study of Latinos

BACKGROUND

Biomarker variability, which includes within-individual variability (CV_I), between-individual variability (CV_G) and methodological variability (CV_P+A) is an important determinant of our ability to detect biomarker-disease associations. Estimates of CV_I and CV_G may be population specific and little data exists on biomarker variability in diverse Hispanic populations. Hence, we evaluated all 3 components of biomarker variability in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) using repeat blood collections (n=58) and duplicate blood measurements (n=761-929 depending on the biomarker).

METHODS

We estimated the index of individuality (II) ((CV_I+CV_P+A)/CV_G) for 41 analytes and evaluated differences in the II across sexes and age groups.

RESULTS

Biomarkers such as fasting glucose, triglycerides and ferritin had substantially higher inter-individual variability and lower II in HCHS/SOL as compared to the published literature. We also found significant sex-specific differences in the II for neutrophil count, platelet count, hemoglobin, % eosinophils and fasting glucose. The II for fasting insulin, post oral glucose tolerance test glucose and cystatin C was significantly higher among the 18-44y age group as compared to the 45+y age group.

CONCLUSIONS

The implications of these findings for determining biomarker-disease associations in Hispanic populations need to be evaluated in future studies.

The Uncertainty of the eGFR

The estimated glomerular filtration rate (eGFR) is a parameter derived from the serum creatinine, patient age and gender and is used to ascertain renal function. It is subject to variation because of the analytical error of the creatinine measurement and biological variation. The widespread use of the eGFR to classify renal disease has led to the identification of more patients with marginal chronic kidney disease but because of the uncertainty of the eGFR it has also led to over-diagnosis of some kidney disease. There is a well described age relation with eGFR.The uncertainty of the eGFR at the critical decision level of 60 mL/min/1.73 m(2) is calculated to be 11. Caution needs to be exercised when interpreting an eGFR between 49 and 71 mL/min/1.73 m(2).

A multicenter evaluation of sweat chloride concentration and variation in infants with cystic fibrosis

Fifty-nineCF infants' sweat chloride concentrations were analyzed to answer the questions: What is the biological and analytical variation in sweat chloride concentrations collected from the 32 infants homozygous for the F508 deletion? Do sweat chloride concentrations change in the first year of life beyond the variance previously established for adults with similar CFTR mutations? The biological and analytical variation of the infants' sweat chloride concentration was similar to that seen in adult CF patients. While there was a statistically significant difference between sweat chloride concentration in early (89.8 mmol/L) and late (95.0 mmol/L) infancy, this change is not likely clinically significant. This suggests that sweat chloride concentrations in CF patients do not change in a meaningful way during the first year of life. Determining variability in infants with CF is the necessary first step for future design of clinical trials of CFTR modulators in younger patients.

Analytical performance of cardiac troponin assays - Current status and future needs

Concurrent with the introduction of cardiac troponin measurements into the diagnostic definition of myocardial infarction (MI), clinicians and laboratory professionals signaled a clear clinical need for improved analytical quality. This was an important precipitant for developing high-sensitivity cardiac troponin (hs-cTn) assays, currently used in rapid algorithms guiding investigations of patients presenting to the emergency department with possible MI. The hs-cTn assays were also important for the detection and monitoring of low-grade chronic myocardial injury, a condition that has been linked to increased long-term risk of cardiovascular morbidity and mortality. This review summarizes the general recommendations for defining analytical performance specifications while providing relevant clinical situations related to analytical performance. Importantly, outcome studies suggest analytical quality performance for hs-cTn is sufficient for early discharge of patients investigated for possible MI. However, bias due to change in calibrators or reagents may significantly affect the percentage of patients discharged. Biological variation data is suitable for defining performance specifications when hs-cTn measurements are used for diagnosing and monitoring chronic myocardial injury. Further improvement in analytical performance for hs-cTn testing may result in even faster decision making in the emergency setting; while also identifying those with chronic injury at risk for an adverse cardiac event.

Biological variation of secretoneurin; a novel cardiovascular biomarker implicated in arrhythmogenesis

BACKGROUND

Secretoneurin is a novel prognostic biomarker that may predict mortality in heart failure and the occurrence of ventricular arrhythmias. This study reports the within subject variation (CVI), between subject variation (CVG), reference change values (RCV) and index of individuality (II) of secretoneurin.

METHODS

Thirty healthy volunteers were included. Non-fasting samples were obtained between 8 and 10 am once a week for ten weeks. Secretoneurin was analyzed in duplicate using ELISA. No outliers were present according to Burnett and Reeds' criteria. Simple linear regression did not identify significant trends. Variance homogeneity in the analytical variance and CVI were tested using Cochrane's and Bartlett's tests and four participants were excluded. Calculation of CVI, CVG and RCV were done on ln transformed data as described by Fokkema, the II was calculated using retransformed data.

RESULTS

The median age of the participants was 36 years and 53% were female. Non-fasting glucose, eGFR(CKD-EPI), cTnT and NT-proBNP concentrations were within the normal range. Median secretoneurin concentrations were 38 pmol/L (women) and 33 pmol/L (men), p-value < 0.001. CVI and CVG were 9.8% (CI 8.7% to 11.0%) and 20.0 (CI 15.4% to 28.0%), respectively. RCV were 38.7% (CI 35.5% to 42.7%) and -27.9 (CI -29.9 to -26.2) and the II were 0.60 (CI 0.42-0.78). No gender differences were present.

CONCLUSION

Secretoneurin has a fairly low CVI, CVG, RCV and II, indicating that it could be suitable as a diagnostic or prognostic biomarker and that delta values in serial samplings may be preferable for identifying clinical changes.

Is pre-biopsy serum prostate specific antigen retesting always justified? A study of the influence of individual and analytical factors on decision making for biopsy referral

BACKGROUND AND AIMS

We investigated factors influencing pre-biopsy prostate-specific antigen (PSA) retesting as recommended by clinical guidelines.

MATERIALS AND METHODS

333 patients screened for prostate cancer (PCa) repeated PSA (Roche Cobas systems) after a median of 3.9 months, before performing biopsy. Multiple regression models were used to assess effects of patients' characteristics on PSA results and changes over time.

RESULTS

PCa [n = 132 (40.7%)] and cancer-free [n = 192 (59.3%)] patients had similar rate of PSA positive results at baseline (84.8% vs. 83.9%, P = 0.931). Their rate of reversion to normal PSA after retesting was negligible (0.9% in PCa and 3.7% in PCa-free patients, P = 0.286). 31.1% of PCa and 31.3% of cancer-free patients (P = 0.426) showed a significant PSA increase after retesting. Age was a confounder since not only PSA increased in older PCa patients, but it was also related to PCa histological grade, in turn associated to PSA increase. In PCa-free patients, glandular inflammation, present in 1/3 of subjects, was also associated to higher PSA concentrations.

CONCLUSION

When obtained with the same immunoassay under controlled analytical conditions, a PSA positive result is confirmed after retesting in the great majority of screened patients. Neither analytical factors nor intraindividual variability appeared to justify PSA retesting before biopsy referral.

Analytical and between-subject variation of thrombin generation measured by calibrated automated thrombography on plasma samples

BACKGROUND

The Calibrated Automated Thrombography (CAT) is an in vitro thrombin generation (TG) assay that holds promise as a valuable tool within clinical diagnostics. However, the technique has a considerable analytical variation, and we therefore, investigated the analytical and between-subject variation of CAT systematically. Moreover, we assess the application of an internal standard for normalization to diminish variation.

METHODS

20 healthy volunteers donated one blood sample which was subsequently centrifuged, aliquoted and stored at -80 °C prior to analysis. The analytical variation was determined on eight runs, where plasma from the same seven volunteers was processed in triplicates, and for the between-subject variation, TG analysis was performed on plasma from all 20 volunteers. The trigger reagents used for the TG assays included both PPP reagent containing 5 pM tissue factor (TF) and PPPlow with 1 pM TF. Plasma, drawn from a single donor, was applied to all plates as an internal standard for each TG analysis, which subsequently was used for normalization.

RESULTS

The total analytical variation for TG analysis performed with PPPlow reagent is 3-14% and 9-13% for PPP reagent. This variation can be minimally reduced by using an internal standard but mainly for ETP (endogenous thrombin potential). The between-subject variation is higher when using PPPlow than PPP and this variation is considerable higher than the analytical variation.

CONCLUSION

TG has a rather high inherent analytical variation but considerable lower than the between-subject variation when using PPPlow as reagent.

Are Your Laboratory Data Reproducible? The Critical Role of Imprecision from Replicate Measurements to Clinical Decision-making

Measurement results of biological samples are not perfect and vary because of numerous factors related to the biological samples themselves and the measurement procedures used to analyze them. The imprecision in patients' laboratory data arising from the measurement procedure, known as analytical variation, depends on the conditions under which the data are collected. Additionally, the sample type and sampling time significantly affect patients' laboratory results, particularly in serial measurements using samples collected at different time points. For accurate interpretation of patients' laboratory data, imprecision-both its analytical and biological components-should be properly evaluated and incorporated into data management. With advancements in measurement technologies, analytical imprecision can be minimized to an insignificant level compared to biological imprecision, which is inherent to all biomolecules because of the dynamic nature of metabolism. This review addresses: (i) the theoretical background of variation, (ii) the statistical and metrological evaluation of measurement variation, (iii) the assessment of variation under different conditions in medical laboratories, (iv) the impact of measurement variation on clinical decisions, (v) the influence of biases on measurement variation, and (vi) the variability of analytes in human metabolism. Collectively, both analytical and biological imprecision are inseparable aspects of all measurements in biological samples, with biological imprecision serving as the foundation of personalized laboratory medicine.

Biological variation estimates for serum neurofilament light chain in healthy subjects

OBJECTIVES

Neurofilament light chain (NfL) is an emerging biomarker of neurodegeneration disorders. Knowledge of the biological variation (BV) can facilitate proper interpretation between serial measurements. Here BV estimates for serum NfL (sNfL) are provided.

METHODS

Serum samples were collected weekly from 24 apparently healthy subjects for 10 consecutive weeks and analyzed in duplicate using the Siemens Healthineers sNfL 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 and the associated reference change values (RCV) and analytical performance specifications (APS).

RESULTS

Despite observed differences in sNfL concentrations between males and females, BV estimates remained consistent across genders. Both within-subject BV (CVI) for males (10.7%, 95%CI; 9.2-12.6) and females (9.1%, 95%CI; 7.8-10.9) and between-subject BV (CVG) for males (26.1%, 95%CI; 18.0-45.6) and females (30.2%, 95%CI; 20.9-53.5) were comparable. An index of individuality value of 0.33 highlights significant individuality, indicating the potential efficacy of personalized reference intervals in patient monitoring.

CONCLUSIONS

The established BV estimates for sNfL underscore its potential as a valuable biomarker for monitoring neurodegenerative diseases, offering a foundation for improved decision-making in clinical settings.