Sex-Specific 99th Percentile Upper Reference Limits for High Sensitivity Cardiac Troponin Assays Derived Using a Universal Sample Bank.

BACKGROUND: How to select healthy reference subjects in deriving 99th percentiles for cardiac troponin assays still needs to be clarified. To assist with global implementation of high sensitivity (hs)-cardiac troponin (cTn) I and hs-cTnT assays in clinical practice, we determined overall and sex-specific 99th percentiles in 9 hs-cTnI and 3 hs-cTnT assays using a universal sample bank (USB). METHODS: The Universal Sample Bank (USB) comprised healthy subjects, 426 men and 417 women, screened using a health questionnaire. Hemoglobin A1c (>URL 6.5%), NT-proBNP (>URL 125 ng/L) and eGFR (<60 mL/min), were used as surrogate biomarker exclusion criteria along with statin use. 99th percentiles were determined by nonparametric, Harrell--Davis bootstrap, and robust methods. RESULTS: Subjects were ages 19 to 91 years, Caucasian 58%, African American 27%, Pacific Islander/Asian 11%, other 4%, Hispanic 8%, and non-Hispanic 92%. The overall and sex-specific 99th percentiles for all assays, before and after exclusions (n = 694), were influenced by the statistical method used, with substantial differences noted between and within both hs-cTnI and hs-cTnT assays. Men had higher 99th percentiles (ng/L) than women. The Roche cTnT and Beckman and Abbott cTnI assays (after exclusions) did not measure cTn values at ≥ the limit of detection in ≥50% women. CONCLUSIONS: Our findings have important clinical implications in that sex-specific 99th percentiles varied according to the statistical method and hs-cTn assay used, not all assays provided a high enough percentage of measurable concentrations in women to qualify as a hs-assay, and the surrogate exclusion criteria used to define normality tended to lower the 99th percentiles.

Fibroblast growth factor 23, high-sensitivity cardiac troponin, and left ventricular hypertrophy in CKD.

BACKGROUND: Detectable levels of cardiac troponins are common in individuals with chronic kidney disease (CKD), even in the absence of symptomatic cardiovascular disease. Abnormal cardiac troponin values are associated with coronary artery disease and left ventricular hypertrophy (LVH) and predict poor clinical outcomes. Elevated levels of fibroblast growth factor 23 (FGF-23) contribute to LVH in CKD. We investigated the association of FGF-23 and hs-cTnI (high-sensitivity cardiac troponin I) and hs-cTnT (high-sensitivity cardiac troponin T) levels in CKD and examined the role of LVH in this association. STUDY DESIGN: Cross-sectional observational study. SETTING & PARTICIPANTS: 153 stable outpatients with non-dialysis-dependent CKD. PREDICTOR: The primary predictor was FGF-23 level. OUTCOMES: hs-cTnI, hs-cTnT. MEASUREMENTS: FGF-23, hs-cTnI, hs-cTnT; left ventricular mass index (LVMI) assessed by echocardiography; coronary artery calcification (CAC) measured by computed tomography. LVMI and CAC were evaluated as potential mediators of the effect of FGF-23 on hs-cTnI/T. RESULTS: Mean age was 64 ± 12 (SD) years, mean estimated glomerular filtration rate was 34 ± 11 mL/min/1.73 m(2), median FGF-23 level was 120 (25th-75th percentile, 79-223) reference unit (RU)/mL, median hs-cTnI level was 6.5 (25th-75th percentile, 3.5-14.5) pg/mL, and median hs-cTnT level was 16.8 (25th-75th percentile, 11.1-33.9) pg/mL. cTnI and cTnT concentrations were higher than the 99th percentile of a healthy population in 42% and 61% of patients, respectively. In unadjusted and multivariable-adjusted analyses, hs-cTnI/T levels were associated significantly with FGF-23 levels. Adjusting for LVMI, but not CAC, weakened the association of FGF-23 and hs-cTnI/T levels. LIMITATIONS: Vitamin D levels were not measured. The prevalence of coronary artery disease may have been underestimated because it was ascertained by self-report. CONCLUSIONS: Minimally elevated cTnI and cTnT levels, detectable by high-sensitivity assays, are associated with elevated FGF-23 levels in stable outpatients with CKD. FGF-23-associated LVH may contribute to detectable hs-cTnI/T levels observed in non-dialysis-dependent patients with CKD.

Interpreting cardiac troponin results from high-sensitivity assays in chronic kidney disease without acute coronary syndrome.

BACKGROUND: Quantification and comparison of high-sensitivity (hs) cardiac troponin I (cTnI) and cTnT concentrations in chronic kidney disease (CKD) have not been reported. We examined the associations between hs cTnI and cTnT, cardiovascular disease, and renal function in outpatients with stable CKD. METHODS: Outpatients (n = 148; 16.9% with prior myocardial infarction or coronary revascularization) with an estimated glomerular filtration rate (eGFR) of <60 mL · min⁻¹ · (1.73 m²)⁻¹ had serum cTnI (99th percentile of a healthy population = 9.0 ng/L), and cTnT (99th percentile = 14 ng/L) measured with hs assays. Left ventricular ejection fraction (LVEF) and mass were assessed by echocardiography, and coronary artery calcification (CAC) was determined by computed tomography. Renal function was estimated by eGFR and urine albumin/creatinine ratio (UACR). RESULTS: The median (interquartile range) concentrations of cTnI and cTnT were 6.3 (3.4-14.4) ng/L and 17.0 (11.2-31.4) ng/L, respectively; 38% and 68% of patients had a cTnI and cTnT above the 99th percentile, respectively. The median CAC score was 80.8 (0.7-308.6), LV mass index was 85 (73-99) g/m², and LVEF was 58% (57%-61%). The prevalences of prior coronary disease events, CAC score, and LV mass index were higher with increasing concentrations from both hs cardiac troponin assays (P < 0.05 for all). After adjustment for demographics and risk factors, neither cardiac troponin assay was associated with CAC, but both remained associated with LV mass index as well as eGFR and UACR. CONCLUSIONS: Increased hs cTnI and cTnT concentrations are common in outpatients with stable CKD and are influenced by both underlying cardiac and renal disease.

Assessing Phlebotomy Device Preference and Specimen Quality in an Oncology Outpatient Clinic.

BACKGROUND: Oncology patients have frequent venipunctures, which causes scarring, making subsequent draws difficult and painful. Novel blood collection systems may decrease discomfort in patients experiencing repeat blood draws. METHODS: Oncology outpatients (n = 101; criteria excluded 12) were recruited to determine their preference for either of two blood collection systems, the 23-gauge standard BD Vacutainer Push Button Blood Collection Set (Standard Push Button system) or the 25-gauge BD Vacutainer UltraTouch Push Button Blood Collection Set (UltraTouch Push Button system). Subjects received two blinded, randomized blood draws, one with each device and just one device for each arm. Subjects subsequently rated their blinded preference for blood collection system. Specimen quality was assessed for each device with measurements for plasma hemoglobin (Shimadzu UV-1800 spectrophotometer, Shimadzu), lactate dehydrogenase, and potassium (Vitros 4600/5600 analyzer, Ortho Diagnostics). RESULTS: Preference for the 25-gauge UltraTouch Push Button system over the 23-gauge Standard Push Button system was significant (UltraTouch, n = 51; Standard n = 30; no preference, n = 8; P = 0.0196). Regarding sample quality, the 25-gauge UltraTouch Push Button system had significantly lower plasma hemoglobin (average 5.34 mg/dL) vs the 23-gauge Standard Push Button system (9.37 mg/dL; P < 0.0001); serum lactate dehydrogenase and potassium differences were not statistically significant. CONCLUSION: Subjects in an oncology clinic preferred phlebotomy with the 25-gauge UltraTouch Push Button system, and samples using this device had less hemolysis as assessed by plasma hemoglobin.

Performance of 4 Automated SARS-CoV-2 Serology Assay Platforms in a Large Cohort Including Susceptible COVID-19-Negative and COVID-19-Positive Patients.

BACKGROUND: Anti-SARS-CoV-2 serological responses may have a vital role in controlling the spread of the disease. However, the comparative performance of automated serological assays has not been determined in susceptible patients with significant comorbidities. METHODS: In this study, we used large numbers of samples from patients who were negative (n = 2030) or positive (n = 112) for COVID-19 to compare the performance of 4 serological assay platforms: Siemens Healthineers Atellica IM Analyzer, Siemens Healthineers Dimension EXL Systems, Abbott ARCHITECT, and Roche cobas. RESULTS: All 4 serology assay platforms exhibited comparable negative percentage of agreement with negative COVID-19 status ranging from 99.2% to 99.7% and positive percentage of agreement from 84.8% to 87.5% with positive real-time reverse transcriptase PCR results. Of the 2142 total samples, only 38 samples (1.8%) yielded discordant results on one or more platforms. However, only 1.1% (23/2030) of results from the COVID-19-negative cohort were discordant. whereas discordance was 10-fold higher for the COVID-19-positive cohort, at 11.3% (15/112). Of the total 38 discordant results, 34 were discordant on only one platform. CONCLUSIONS: Serology assay performance was comparable across the 4 platforms assessed in a large population of patients who were COVID-19 negative with relevant comorbidities. The pattern of discordance shows that samples were discordant on a single assay platform, and the discordance rate was 10-fold higher in the population that was COVID-19 positive.

Impact of increased body mass index on accuracy of B-type natriuretic peptide (BNP) and N-terminal proBNP for diagnosis of decompensated heart failure and prediction of all-cause mortality.

BACKGROUND: BNP and N-terminal proBNP (NT-proBNP) concentrations may be depressed in patients with increased body mass index (BMI). Whether increased BMI affects accuracy of these biomarkers for diagnosing decompensated heart failure (HF) and predicting outcomes is unknown. METHODS: We measured BNP and NT-proBNP in 685 patients with possible decompensated HF in a free-living community population subdivided by BMI as obese, overweight, and normal weight. HF diagnosis was adjudicated by a cardiologist blinded to BNP and NT-proBNP results. We tabulated all-cause mortality over a median follow-up of 401 days and assessed marker accuracy for HF diagnosis and mortality by ROC analysis. RESULTS: Of the 685 patients, 40.9% were obese (n = 280), 28.2% were overweight (n = 193), and 30.9% had normal BMI (n = 212). Obese patients had lower BNP and NT-proBNP compared with overweight or normal-weight individuals (P < 0.001) and decreased mortality compared with normal-weight individuals (P < 0.001). Both biomarkers added significantly to a multivariate logistic regression model for diagnosis of decompensated HF across BMI categories. NT-proBNP outperformed BNP for predicting all-cause mortality in normal-weight individuals (chi(2) for BNP = 6.4, P = 0.09; chi(2) for NT-proBNP = 16.5, P < 0.001). Multivariate regression showed that both biomarkers remained significant predictors of decompensated HF diagnosis in each BMI subgroup. CONCLUSIONS: In this study population, obese patients had significantly lower BNP and NT-proBNP that reflected lower mortality. BNP and NT-proBNP can be used in all BMI groups for decompensated HF diagnosis, although BMI-specific cutpoints may be necessary to optimize sensitivity.

Analytical and clinical characterization of a novel high-sensitivity cardiac troponin assay in a United States population.

BACKGROUND: Cardiac troponin (cTn) is the keystone for diagnosis of acute myocardial infarction (AMI). We examined the analytical and clinical diagnostic characteristics of the ACCESS hsTnI assay in a United States (US) population. METHODS: All measurements and studies were conducted using a lithium heparin matrix. Sex-specific 99th percentile upper reference limits (URLs) were determined for 1089 healthy women (54.6%) and men using non-parametric statistics. High-sensitivity (hs) performance was assessed to determine if the total CV was ≤10% at sex-specific URLs, and if ≥50% of cTnI values for each sex exceeded the assay's limit of detection (LoD). Precision, analytical measurement range, high-dose hook effect, and endogenous/exogenous interferences were examined with CLSI guidance. Clinical characterization included serial sampling of 1854 suspected AMI subjects presenting to 14 US Emergency Departments. AMI was adjudicated by a panel of expert cardiologists. The study's only exclusion was end stage renal disease. RESULTS: 99th percentile URLs were 11.6-, 19.8- and 17.5-ng/L for respective female, male and all-subject populations. Total %CV was <8% from 6.8 to 19,000 ng/L, and <6% at sex-specific 99th percentiles; ≥99% of ACCESS hsTnI values for each sex exceeded the LoD. No high-dose hook effect or endogenous/exogenous interferences were identified. A comparison of Baseline samples collected at ≤1 h and any-time after presentation, found 4% lower sensitivity for AMI than with earlier sampling. For 1-9 h post presentation, the sensitivity was >90%, specificity >85%; and negative and positive predictive value were ≥99% and >60%, respectively. CONCLUSION: Analytical and clinical performance of the ACCESS hsTnI assay meets the definition of a hs cTn method. The ACCESS hsTnI assay has good precision over a wide range, no significant interferences, and sensitivity >90% and NPV ≥99%. Performance is appropriate for aiding in AMI diagnosis.

Pivotal findings for a high-sensitivity cardiac troponin assay: Results of the HIGH-US study.

BACKGROUND: Cardiac troponin (cTn) is the keystone for diagnosis of acute myocardial infarction (AMI). We examined the analytical and diagnostic accuracy of the Atellica IM TnIH assay to determine high-sensitivity performance and appropriate diagnostic performance for clinical use. METHODS: Sex-specific 99th percentile upper reference limits (URLs) were determined for a healthy cohort of 1007 women and 1000 men using non-parametric statistics. High-sensitivity performance was assessed by examining if imprecision was ≤10% at sex-specific URLs and if ≥50% of cTnI values for each sex exceeded the assay's limit of detection (LoD) with the AACC Universal Sample Bank. Precision, high-dose hook effect, endogenous/exogenous interferences were examined with CLSI guidance. Clinical characterization was with 2494 suspected AMI subjects presenting to emergency departments across the United States. AMI was adjudicated by expert cardiologists and emergency medicine physicians. There were no comorbidity exclusions. RESULTS: 99th percentile URLs were 34 ng/L, 53 ng/L and 45 ng/L for the female, male and overall populations, respectively. Total imprecision was <5% from 12 ng/L to 16,000 ng/L; ≥55% of cTnI values for each sex exceeded the LoD. No high-dose hook or endogenous/exogenous interferences were identified. After 2.5-3.5 h post presentation the sensitivity and specificity were >90%; negative and positive predictive value were ≥98% and >60%, respectively. Non-AMI subjects with comorbidities and values exceeding 99th percentile URLs had absolute and percent change at 2-4 h that were lower than AMI patients with comorbidities (p = 0.001). CONCLUSION: The Atellica IM TnIH assay is a high-sensitivity method and demonstrates clinical performance appropriate for AMI diagnosis.

Validation of high-sensitivity performance for a United States Food and Drug Administration cleared cardiac troponin I assay.

BACKGROUND: High-Sensitivity (hs) cardiac troponin (cTn) assays are categorized by two criteria: (i) cTn values above the limit of detection (LoD) for >50% of male and female healthy cohorts of ≥300 individuals; (ii) imprecision ≤10% total %CV for sex-specific 99th-percentile clinical decision values (CDVs). No documented hs-Tn assay has yet been FDA-cleared. METHODS: The PATHFAST cTnI-II assay's LoD was 2.3 ng/L using CLSI EP-17. The AACC Universal Sample Bank of 847 healthy men (50.6%) and women (49.4%) was used to determine 99th-percentile CDVs with Nonparametric, Harrell-Davis and Robust modeling. Health/Medication questionnaires and Amino-terminal proBNP, Hemoglobin A1c and estimated Glomerular Filtration Rate surrogates excluded underlying health conditions. RESULTS: The cTnI-II test's total CV was 6.1% at 29 ng/L and 7.1% at 22 ng/L; the LoD was 2.3 ng/L. Of the full 847-member healthy cohort, 113 (13.3%) were excluded by abnormal surrogate biomarkers. The final 734-member healthy population had the following (% > LoD): overall, 487 (66.3%); women, 186 (52.8%); and men, 301 (78.8%). 99th-percentile CDVs by Nonparametric modeling were: 28 ng/L (90% CI: 20-30), overall final 732-member healthy population; 20 ng/L (90% CI: 13-30), 352 women; and 30 ng/L (90% CI: 21-37), 382 men. Differences between sex-specific CDVs were not significantly different (p > .05) with Nonparametric or Harrell-Davis modeling; however, Robust Modeling did show significance (<0.05), with lower CDVs at 11 ng/L (90% CI: 9-12) and 16 ng/L (90% CI: 15-18) for the female and male cohorts, respectively. CONCLUSIONS: cTnI-II is the only FDA-cleared assay that has demonstrated high-sensitivity cTn assay. Use of recommended modeling in >300 healthy subjects for determining sex-specific 99th-percentile CDVs did not show statistically significant differences except with the Robust modeling.

Frequency and cause of cardiac troponin T elevation in chronic hemodialysis patients from study of cardiovascular magnetic resonance.

Cardiac troponin T level predicts a gradient risk for death in patients using hemodialysis. We used cardiovascular magnetic resonance (CMR) to determine whether an asymptomatic increase of troponin T in patients using hemodialysis is associated with subclinical myocardial infarction (MI). Twenty-six patients using long-term hemodialysis (49 +/- 12 years of age, 19 men, 8 diabetics) with left ventricular (LV) ejection fraction >40% and no known coronary artery disease were selected based on a low-risk troponin T level /=0.07 ng/ml (median 0.15, interquartile range 0.09 to 0.19, n = 13). All underwent CMR imaging for LV mass and for MI by late gadolinium enhancement. Between high- and low-risk patients using hemodialysis, there were no differences in age, gender, ethnicity, or diabetes mellitus. Of the high-risk patients, 3 (23%, 95% confidence interval [CI] 5 to 54) had MI by late gadolinium enhancement versus 0 (0%, 95% CI 0 to 25) low-risk patients (p = 0.22). A diffuse, midwall late gadolinium enhancement pattern was seen in 1 high-risk patient (8%) versus 0 low-risk patient (0%, 95% CI 0 to 25, p = 0.97). Height-adjusted LV mass and LV hypertrophy were not significantly different between high-risk (62 +/- 26 g/m(2.7), LV hypertrophy, n = 7, 54%) and low-risk (54 +/- 20 g/m(2.7), LV hypertrophy, n = 5, 39%) patients (p = 0.37 for LV mass, p = 0.69 for LV hypertrophy). In conclusion, MI detected by CMR is present in few patients on hemodialysis with high troponin T levels and absent in the setting of very low troponin T levels, suggesting that additional myocardial pathologies cause increased troponin T in patients using hemodialysis.

Performance of a no-pretreatment tacrolimus assay on the Dade Behring Dimension RxL clinical chemistry analyzer.

BACKGROUND: Therapeutic drug monitoring for tacrolimus is important for organ transplant patients receiving this immunosuppressant. Current available assays for tacrolimus require sample pre-treatment and operate in a batch mode. Here a no-pretreatment tacrolimus assay, performed on the Dade Behring Dimension analyzer is compared to the Abbott IMx tacrolimus assay and to an LC/MS/MS method. METHODS: Whole blood samples from 2 medical centers and different transplant types (kidney n=103, liver n=81, heart n=27, pancreas n=16, bone marrow n=9, [corrected] lung n=7), were obtained and tacrolimus quantified by each of the 3 assays. RESULTS: The lower limit of the linear range was 1.2 ng/ml on the Dimension assay. Total imprecision was 9.8% and within-run imprecision was 9.6% at a tacrolimus concentration of 3.4 ng/dL. Passing-Bablock regression analysis determined the following relationships: DIMN=(1.16) LC/MS - 0.43, r=0.90 and DIMN=(0.99)IMx - 0.35, r=0.87. CONCLUSIONS: The Dade Behring Dimension [corrected] Tacrolimus assay has adequate imprecision and correlates well with the reference method of LC/MS/MS. The assay appears suitable for clinical use, and has the advantages of not requiring a pretreatment step and the ability to be performed in a random-access mode.

Clinical performance characteristics of a new photometric lithium assay: a multicenter study.

BACKGROUND: Therapeutic monitoring of lithium is important because of its narrow therapeutic range and therapeutic index, low protein binding and single route of elimination. We characterized a new photometric method that avoids the specialized requirements of ion-specific electrode (ISE), atomic absorption and flame emission methods. METHODS: Minimum detectable concentration (MDC), linearity and calibration drift over 65 days were determined. Within-run, between-run and total imprecision were assessed over 20 days in accordance with NCCLS EP5. Interference studies were conducted for 46 endogenous and exogenous compounds. Two production lots of the new photometric method (LI) were compared on the Dimension(R) RxL system and two ISE methods [Ciba Corning (n=124) and DuPont (n=131)], an established photometric method (Vitros) 950 system; n=63) and atomic absorption (Thermo-Jerell Ash; n=63). RESULTS: The MDC was 0.04 mmol/l. Linearity was demonstrated from 0.12 to 5.8 mmol/l by the regression equation: observed=(1.01 x expected)-0.0005 mmol/l, S(y/x)=0.03 mmol/l, r=0.999. Drift for the lithium calibrators over the 65-day study period was <5%, except for the lowest calibrator, which showed 0.04 mmol/l drift. None of the 46 potential interfering substances showed greater than a 6.5% difference between control and test solutions. ISE method comparisons showed the following: LI=(1.08 x Ciba Corning ISE)-0.15 mmol/l, S(y/x)=0.05, r=0.999, and LI=(1.03 x DuPont ISE)+0.00 mmol/l, S(y/x)=0.06 mmol/l, r=0.999. Comparison of the LI method with the atomic absorption and Vitros system showed proportionality error <10%. Bias between the LI method and atomic absorption was 7%, substantially less than that documented in proficiency surveys for the Vitros and other systems. No lot-to-lot or site-to-site differences were observed. CONCLUSION: This new photometric method is an attractive alternative for Li measurement and is adaptable to instruments having spectrophotometric capability.

Performance evaluation of blood glucose monitoring devices.

Many new technologies are being applied to measure blood glucose concentrations, but there is a lack of a standardized approach to evaluate performance of these devices. We sought to identify the key elements in evaluating the performance of devices for measuring blood glucose. We examined these elements in a multicenter study of four brands of glucose meters that are commonly used by diabetic patients. We tested control materials, spiked whole blood specimens, and 461 heparinized whole blood specimens in triplicate by each of the four brand glucose meters, and analyzed the plasma glucose concentrations of these specimens by a hexokinase (HK) method that incorporated reference materials developed by National Institute of Standards and Technology. Testing with glucose meters was performed at three sites, with multiple operators, meters, and representative lots of reagents. We evaluated the systematic bias, random error, and clinical significance of glucose meters. Meters were precise with a coefficient of variation of <4% across a wide range of glucose concentrations. Slopes significantly different from 1.0 were observed for two meters with 11-13% and -11% to -13% at the 95% confidence interval level by the linear regression of meter results versus the HK method from 33 to 481 mg/dL (correlation coefficient >0.98 and standard error of estimation S(y/x) <13 mg/dL for both meters). Analysis of the clinical significance of bias by Clarke Error Grid showed that results of the four meters were outside the accurate zone (26.5%, 2.4%, 1.5%, and 5.6%). Only a small number of the results showed clinically significant bias, mostly in the hypoglycemic range. Meters performed consistently throughout the study and, generally, were precise, although precision varied at extremely high or low glucose concentrations. Two of the glucose meters had substantial systematic bias when compared with an HK method, indicating a need for improving calibration and standardization. Analytical performance varied over the physiological range of glucose values so that separate accuracy and precision goals should be defined for hypoglycemic, normoglycemic, and hyperglycemic ranges. This study describes the current state of performance of blood glucose monitoring devices and points out those factors that should be assessed during evaluation of new devices.

Methodological and analytic considerations for blood biomarkers.

Biomarkers typically evolve from a research setting to use in clinical care as evidence for their independent contribution to patient management accumulates. This evidence relies heavily on knowledge of the preanalytical, analytical, and postanalytical characteristics of the biomarker's measurement. For the preanalytical phase, considerations such specimen type, acceptable anticoagulants for blood samples, biologic variation and stability of the biomarker under various conditions are key. The analytical phase entails critical details for development and maintenance of assays having performance characteristics that are "fit for service" for the clinical application at hand. Often, these characteristics describe the ability to measure minute quantities in the biologic matrix used for measurement. Although techniques such as mass spectrometry are used effectively for biomarker discovery, routine quantification often relies on use of immunoassays; early in development, the most common immunoassay used is the enzyme-linked immunosorbent assay format. As biomarkers evolve successfully, they will be adapted to large main laboratory platforms or, depending on the need for speed, point-of-care devices. Users must pay particular attention to performance parameters of assays they are considering for clinical implementation. These parameters include the limit of blank, a term used to describe the limit of analytical noise for an assay; limit of detection, which describes the lowest concentration that can reliably be discriminated from analytical noise; and perhaps most importantly, the limit of quantitation, which is the lowest concentration at which a biomarker can be reliably measured within some predefined specifications for total analytical error that is based on clinical requirements of the test. The postanalytical phase involves reporting biomarker values, which includes reporting units, any normalization factors, and interpretation. Standardization, a process that involves metrological traceability to a primary reference material and definitive measurement method, is important to assure that all biomarker values are transferable in the literature and across institutions. In the absence of standardization, assays can be harmonized using secondary reference materials so that biomarker values can be combined for meta-analysis and interpreted clinically with common reference and decision limit values.

Multi-center determination of galectin-3 assay performance characteristics: Anatomy of a novel assay for use in heart failure.

BACKGROUND: Galectin-3 is a carbohydrate binding protein that plays many important regulatory roles in inflammation, immunity and cancer. Recent studies indicate that galectin-3 is a mediator of heart failure development and progression. Development of an improved assay for galectin-3 measurement was necessary for appropriate clinical assessment. Key analytical performance characteristics, the reference distribution and association of galectin-3 levels with clinical outcome in heart failure patients are defined. METHODS: A two-site ELISA test was examined for measurement matrix, imprecision, limits of blank, detection, and quantitation, as well as linearity, high-dose hook effect, storage stability, cross-reactivity with nine similar compounds, interference with 22 common medications and icterus, lipemia and hemolysis, all in accordance with CLSI guidance. Also the effects of human anti-mouse antibodies and rheumatoid factor on recovery of galectin-3 were investigated. The reference interval was determined for 1092 ostensibly healthy individuals. The association of galectin-3 concentrations with an outcome of mortality was examined in a preliminary analysis of 129 acute decompensated heart failure patients. RESULTS: Galectin-3 results were equivalent when measured in serum or EDTA plasma. Imprecision studies demonstrated that the total CV was <10% at a low concentration of 6 ng/mL, 7% near the mid-level concentration of 21 ng/mL, and 15% at the high level of 70 ng/mL. The limit of blank was 0.86 ng/mL, the limit of detection was 1.13 ng/mL, and the limit of quantitation was 0.96 ng/mL. The linear measurement range was 0.96-130 ng/mL and there was no high-dose hook at levels up to 500 ng/mL. No cross-reactivity with nine compounds structurally related to galectin-3 and no interference from 22 common medications, icterus or lipemia was found. Hemolysis and presence of human anti-mouse antibodies or rheumatoid factor were found to be potential sources of interference. Samples can be stored for up to 15 days at either 22-28 degrees C or 2-8 degrees C before analysis; measurements are stable after storage at -20 degrees C or -70 degrees C for at least 6 months and through six freeze-thaw cycles. The 90th, 95th and 97.5th percentile of the normal reference interval was 17.6, 20.3 and 22.1 ng/mL, respectively. Galectin-3 in the acute decompensated heart failure patients ranged from 4.0 to 75 ng/mL; using a cutpoint of 22.1 ng/mL in an unadjusted analysis, galectin-3 values were associated with an outcome of death (p=0.035). Galectin-3 is associated with severity of heart failure as indicated by NYHA Class (p-value for trend, 0.017). CONCLUSION: This ELISA for galectin-3 measurement demonstrated acceptable analytical characteristics and was associated with mortality in a preliminary unadjusted analysis.

Performance characteristics of a no-pretreatment, random access sirolimus assay for the Dimension RxL clinical chemistry system.

OBJECTIVES: Current therapeutic drug monitoring methods for sirolimus require a manual pre-treatment step and batch analysis. We describe and validate a no-pretreatment, random access sirolimus assay for the Dimension RxL clinical chemistry system from Siemens Healthcare Diagnostics Inc. DESIGN AND METHODS: Whole blood samples from renal transplant patients prescribed sirolimus were analyzed by the LC-MS/MS reference method, Abbott IMx and Dimension RxL methods in accordance with CLSI recommendations. RESULTS: The Dimension sirolimus assay had a functional sensitivity of 2.0 ng/mL and repeatability and within-laboratory imprecision less than 12.6% at 3 ng/mL and less than 5% at 11-12 ng/mL. Least squares linear regression demonstrated the following relationships: RxL=1.20(LC-MS/MS) - 0.70, r=0.95 and RxL=1.33(IMx) - 0.75, r=0.96. CONCLUSIONS: The Dimension sirolimus assay correlates well with the LC-MS/MS reference and IMx immunoassay methods and has the advantage of random access analysis without a manual pre-treatment step.

Cardiovascular disease testing on the Dimension Vista system: biomarkers of acute coronary syndromes.

OBJECTIVES: Performance characteristics of the LOCI cTnI, CK-MB, MYO, NTproBNP and hsCRP methods on the Dimension Vista System were evaluated. DESIGN AND METHODS: Imprecision (following CLSI EP05-A2 guidelines), limit of quantitation (cTnI), limit of blank, linearity on dilution, serum versus plasma matrix studies (cTnI), and method comparison studies were conducted. RESULTS: Method imprecision of 1.8 to 9.7% (cTnI), 1.8 to 5.7% (CK-MB), 2.1 to 2.2% (MYO), 1.6 to 3.3% (NTproBNP), and 3.5 to 4.2% (hsCRP) were demonstrated. The manufacturer's claimed imprecision, detection limits and upper measurement limits were met. Limit of Quantitation was 0.040 ng/mL for the cTnI assay. Agreement of serum and plasma values for cTnI (r=0.99) was shown. Method comparison study results were acceptable. CONCLUSIONS: The Dimension Vista cTnI, CK-MB, MYO, NTproBNP, and hsCRP methods demonstrate acceptable performance characteristics for use as an aid in the diagnosis and risk assessment of patients presenting with suspected acute coronary syndromes.