An updated protocol based on CLSI document C37 for preparation of off-the-clot serum from individual units for use alone or to prepare commutable pooled serum reference materials.

Manufacturers of in vitro diagnostic medical devices, clinical laboratories, research laboratories and calibration laboratories require commutable reference materials that can be used in the calibration hierarchies of medical laboratory measurement procedures used for human specimens to establish metrological traceability to higher order reference systems. Commutable materials are also useful in external quality assessment surveys. In order to achieve these goals, matrix-based reference materials with long-term stability, appropriate measurand concentrations and commutability with individual human specimens are required. The Clinical and Laboratory Standards Institute (CLSI) guideline C37-A (now archived) provided guidance to prepare commutable pooled serum reference materials for use in the calibration hierarchies of cholesterol measurement procedures. Experience using the C37-A guideline has identified a number of technical enhancements as well as applications to measurands other than cholesterol. This experience is incorporated into this updated protocol to ensure the procedure will continue to meet the needs of the medical laboratory. The updated protocol describes a procedure for preparing frozen human serum units or pools with minimal matrix alterations that are likely to be commutable with individual human serum samples. The protocol provides step-by-step guidance for the planning phase, collection of individual serum units, processing the units, qualifying the units for use in a pool and frozen storage of aliquots of pooled sera to manufacture frozen serum pools. Guidance on how to perform quality control of the final product and suggestions on documentation are also provided.

Traceability in laboratory medicine: a global driver for accurate results for patient care.

Laboratory medicine results influence a high percentage of all clinical decisions. Globalization requires that laboratory medicine results should be transferable between methods in the interests of patient safety. International collaboration is necessary to deliver this requirement. That collaboration should be based on traceability in laboratory medicine and the adoption of higher order international commutable reference materials and measurement procedures. Application of the metrological traceability chain facilitates a universal approach. The measurement of serum cholesterol and blood HbA1c serve as examples of the process of method standardization where an impact on clinical outcomes is demonstrable. The measurement of plasma parathyroid hormone and blood HbA2 serve as examples where the current between-method variability is compromising patient management and method standardization and/or harmonization is required. Challenges to the widespread adoption of traceability in laboratory medicine include the availability of reference materials and methods, geographical differences, the use of variable units, complex analytes and limited global coordination. The global collaboration requires the involvement of several different stakeholder groups ranging from international experts to laboratory medicine specialists in routine clinical laboratories. A coordinated action plan is presented with actions attributable to each of these stakeholder groups.

Difference in bias approach for commutability assessment: application to frozen pools of human serum measured by 8 direct methods for HDL and LDL cholesterol.

BACKGROUND: We used a difference in bias approach to evaluate the commutability of 4 frozen serum pools for 8 direct methods for measurement of HDL and LDL cholesterol (HDLC and LDLC). METHODS: Freshly collected nonfrozen sera from 138 diseased and 37 nondiseased patients and 4 frozen pools from the CDC Lipid Standardization Program were measured by direct methods and by the beta-quantification reference measurement procedure of the CDC. We used an error components model to estimate the difference in the bias component of error plus its uncertainty for frozen pools vs patient samples between the direct method and the reference procedure. Frozen pools with bias differences less than a critical value determined by either medical requirements for bias or the random error components of the measurement procedures were considered commutable. RESULTS: On the basis of medical requirement criteria, 1 of the 4 frozen pools was commutable for most of the HDLC methods for both diseased and nondiseased patients, and none was commutable for LDLC methods. On the basis of random error criteria, all of the frozen pools were generally commutable for all of the HDLC methods for both diseased and nondiseased patients, and 1 of the 4 frozen pools was generally commutable for most of the LDLC methods for both diseased and nondiseased patients. CONCLUSIONS: Commutability was assessed as the closeness of agreement of the difference in bias between a reference material and a set of patient samples. Criteria for commutability could be based on fixed medical requirements for bias or on random error components.

Large-Scale Scientific Study Led by a Professional Organization during the COVID-19 Pandemic: Operations, Best Practices, and Lessons Learned.

In 2021, the Association for Diagnostics & Laboratory Medicine (ADLM) (formerly the American Association for Clinical Chemistry [AACC]) developed a scientific study that aimed to contribute to the understanding of SARS-CoV-2 immunity during the evolving course of the pandemic. This study was led by a group of expert member volunteers and resulted in survey data from 975 individuals and blood collection from 698 of those participants. This paper describes the formulation and execution of this large-scale scientific study, encompassing best practices and insights gained throughout the endeavor.

Proposed serum cholesterol reference measurement procedure by gas chromatography-isotope dilution mass spectrometry.

BACKGROUND: Our purpose was to establish a mass spectrometry reference measurement procedure (RMP) for cholesterol to use in the CDC's standardization programs. We explored a gas chromatography-isotope dilution mass spectrometry (GC-IDMS) procedure using a multilevel standard calibration curve to quantify samples with varying cholesterol concentrations. METHODS: We calibrated the mass spectrometry instrument by isotope dilution with a pure primary standard reference material and an isotopically enriched cholesterol analog as the internal standard (IS). We diluted the serum samples with Tris-HCl buffer (pH 7.4, 0.05 mol/L, 0.25% Triton X-100) before analysis. We used 17 serum pools, 10 native samples, and 2 standard reference materials (SRMs). We compared the GC-IDMS measurements with the CDC's modified Abell-Levy-Brodie-Kendall (AK) RMP measurements and assessed method accuracy by analyzing 2 SRMs. We evaluated the procedure for lack of interference by analyzing serum spiked with a mixture of 7 sterols. RESULTS: The mean percent bias between the AK and the GC-IDMS RMP was 1.6% for all samples examined. The mean percent bias from NIST's RMP was 0.5% for the SRMs. The total %CVs for SRM 1951b levels I and II were 0.61 and 0.73%, respectively. We found that none of the sterols investigated interfered with the cholesterol measurement. CONCLUSIONS: The low imprecision, linear response, lack of interferences, and acceptable bias vs the NIST primary RMP qualifies this procedure as an RMP for determining serum cholesterol. The CDC will adopt and implement this GC-IDMS procedure for cholesterol standardization.

Roadmap for harmonization of clinical laboratory measurement procedures.

Results between different clinical laboratory measurement procedures (CLMP) should be equivalent, within clinically meaningful limits, to enable optimal use of clinical guidelines for disease diagnosis and patient management. When laboratory test results are neither standardized nor harmonized, a different numeric result may be obtained for the same clinical sample. Unfortunately, some guidelines are based on test results from a specific laboratory measurement procedure without consideration of the possibility or likelihood of differences between various procedures. When this happens, aggregation of data from different clinical research investigations and development of appropriate clinical practice guidelines will be flawed. A lack of recognition that results are neither standardized nor harmonized may lead to erroneous clinical, financial, regulatory, or technical decisions. Standardization of CLMPs has been accomplished for several measurands for which primary (pure substance) reference materials exist and/or reference measurement procedures (RMPs) have been developed. However, the harmonization of clinical laboratory procedures for measurands that do not have RMPs has been problematic owing to inadequate definition of the measurand, inadequate analytical specificity for the measurand, inadequate attention to the commutability of reference materials, and lack of a systematic approach for harmonization. To address these problems, an infrastructure must be developed to enable a systematic approach for identification and prioritization of measurands to be harmonized on the basis of clinical importance and technical feasibility, and for management of the technical implementation of a harmonization process for a specific measurand.

Non-HDL cholesterol shows improved accuracy for cardiovascular risk score classification compared to direct or calculated LDL cholesterol in a dyslipidemic population.

BACKGROUND: Our objective was to evaluate the accuracy of cardiovascular disease (CVD) risk score classification by direct LDL cholesterol (dLDL-C), calculated LDL cholesterol (cLDL-C), and non-HDL cholesterol (non-HDL-C) compared to classification by reference measurement procedures (RMPs) performed at the CDC. METHODS: We examined 175 individuals, including 138 with CVD or conditions that may affect LDL-C measurement. dLDL-C measurements were performed using Denka, Kyowa, Sekisui, Serotec, Sysmex, UMA, and Wako reagents. cLDL-C was calculated by the Friedewald equation, using each manufacturer's direct HDL-C assay measurements, and total cholesterol and triglyceride measurements by Roche and Siemens (Advia) assays, respectively. RESULTS: For participants with triglycerides<2.26 mmol/L (<200 mg/dL), the overall misclassification rate for the CVD risk score ranged from 5% to 17% for cLDL-C methods and 8% to 26% for dLDL-C methods when compared to the RMP. Only Wako dLDL-C had fewer misclassifications than its corresponding cLDL-C method (8% vs 17%; P<0.05). Non-HDL-C assays misclassified fewer patients than dLDL-C for 4 of 8 methods (P<0.05). For participants with triglycerides≥2.26 mmol/L (≥200 mg/dL) and<4.52 mmol/L (<400 mg/dL), dLDL-C methods, in general, performed better than cLDL-C methods, and non-HDL-C methods showed better correspondence to the RMP for CVD risk score than either dLDL-C or cLDL-C methods. CONCLUSIONS: Except for hypertriglyceridemic individuals, 7 of 8 dLDL-C methods failed to show improved CVD risk score classification over the corresponding cLDL-C methods. Non-HDL-C showed overall the best concordance with the RMP for CVD risk score classification of both normal and hypertriglyceridemic individuals.

Validation of CKD and related conditions in existing data sets: A systematic review.

BACKGROUND: Accurate classification of individuals with kidney disease is vital to research and public health efforts aimed at improving health outcomes. Our objective is to identify and synthesize published literature evaluating the accuracy of existing data sources related to kidney disease. STUDY DESIGN: A systematic review of studies seeking to validate the accuracy of the underlying data relevant to kidney disease. SETTING & POPULATION: US-based and international studies covering a wide range of both outpatient and inpatient study populations. SELECTION CRITERIA FOR STUDIES: Any English-language study investigating the prevalence or cause of kidney disease, existence of comorbid conditions, or cause of death in patients with chronic kidney disease (CKD). All definitions and stages of CKD, including end-stage renal disease (ESRD), were accepted. INDEX TESTS: Presence of a kidney disease-related variable in existing data sets, including administrative data sets and disease registries. REFERENCE TESTS: Presence of a kidney disease-related variable defined using laboratory criteria or medical record review. RESULTS: 30 studies were identified. Most studies investigated the accuracy of kidney disease reporting, comparing coded renal disease with that defined using estimated glomerular filtration rate. The sensitivity of coded renal disease varied widely (0.08-0.83). Specificity was higher, with all studies reporting values ≥0.90. Studies evaluating the cause of CKD, comorbid conditions, and cause of death in patients with CKD used ESRD or transplant populations exclusively, and accuracy was highly variable compared with ESRD registry data. LIMITATIONS: Only English-language studies were evaluated. CONCLUSIONS: Given the heterogeneous results of validation studies, a variety of attributes of existing data sources, including the accuracy of individual data items within these sources, should be considered carefully before use in research, quality improvement, and public health efforts.

Seven direct methods for measuring HDL and LDL cholesterol compared with ultracentrifugation reference measurement procedures.

BACKGROUND: Methods from 7 manufacturers and 1 distributor for directly measuring HDL cholesterol (C) and LDL-C were evaluated for imprecision, trueness, total error, and specificity in nonfrozen serum samples. METHODS: We performed each direct method according to the manufacturer's instructions, using a Roche/Hitachi 917 analyzer, and compared the results with those obtained with reference measurement procedures for HDL-C and LDL-C. Imprecision was estimated for 35 runs performed with frozen pooled serum specimens and triplicate measurements on each individual sample. Sera from 37 individuals without disease and 138 with disease (primarily dyslipidemic and cardiovascular) were measured by each method. Trueness and total error were evaluated from the difference between the direct methods and reference measurement procedures. Specificity was evaluated from the dispersion in differences observed. RESULTS: Imprecision data based on 4 frozen serum pools showed total CVs <3.7% for HDL-C and <4.4% for LDL-C. Bias for the nondiseased group ranged from -5.4% to 4.8% for HDL-C and from -6.8% to 1.1% for LDL-C, and for the diseased group from -8.6% to 8.8% for HDL-C and from -11.8% to 4.1% for LDL-C. Total error for the nondiseased group ranged from -13.4% to 13.6% for HDL-C and from -13.3% to 13.5% for LDL-C, and for the diseased group from -19.8% to 36.3% for HDL-C and from -26.6% to 31.9% for LDL-C. CONCLUSIONS: Six of 8 HDL-C and 5 of 8 LDL-C direct methods met the National Cholesterol Education Program total error goals for nondiseased individuals. All the methods failed to meet these goals for diseased individuals, however, because of lack of specificity toward abnormal lipoproteins.

National Academy of Clinical Biochemistry Laboratory Medicine Practice guidelines: emerging biomarkers for primary prevention of cardiovascular disease.

BACKGROUND: Heart disease and stroke continue to be the leading causes of death in the US. As a result, investigators continue to look for new and emerging biomarkers of disease risk. Because many of these emerging biomarkers are not as well documented as those of conventional lipid and lipoprotein risk factors, their value in clinical practice needs to be critically appraised and appropriate guidelines developed for their proposed use. CONTENT: The National Academy of Clinical Biochemistry (NACB) convened a multidisciplinary expert panel to develop laboratory medicine practice guidelines for a selected subset of these emerging risk factors as applied in a primary prevention setting of heart disease and stroke. The NACB expert panel selected lipoprotein subclasses and particle concentration, lipoprotein(a), apolipoproteins A-I and B, high sensitivity C-reactive protein (hsCRP), fibrinogen, white blood cell count, homocysteine, B-type natriuretic peptide (BNP), N-terminal proBNP (NT-proBNP), and markers of renal function as biomarkers that fell within the scope of these guidelines. CONCLUSIONS: Based on a thorough review of the published literature, only hsCRP met all of the stated criteria required for acceptance as a biomarker for risk assessment in primary prevention.

Standardization of high-sensitivity immunoassays for measurement of C-reactive protein; II: Two approaches for assessing commutability of a reference material.

BACKGROUND: We evaluated the commutability of a proposed reference material (PRM), with a formulation based on dilution of Certified Reference Material 470 (CRM470), for 24 high-sensitivity C-reactive protein (hsCRP) methods. We also investigated whether calibration by use of PRM was effective in harmonizing results. METHODS: A set of 40 native clinical samples was measured along with PRM and 3 dilutions of PRM. We used weighted least-squares polynomial regression (WLS/PR) to perform comparisons between all method combinations and to calculate normalized residuals for the PRM. The PRM was considered noncommutable if any of the normalized residuals for a method pair was >2. Correspondence analysis (CA) was used to explore the multidimensional relationships between methods and samples to evaluate if the PRM had properties similar to native clinical samples. Clinical sample results from the methods for which PRM was commutable were recalibrated based on the PRM results, and ANOVA was used to estimate the CVs before and after recalibration. RESULTS: After omitting data for 9 methods because of poor precision or procedural flaws, we used data from the 15 remaining methods to evaluate commutability. Using both WLS/PR and CA we found that PRM was noncommutable with 1 method. We found modest improvement in total and among-method CVs when PRM was used to harmonize the results from the 14 methods for which it was commutable. CONCLUSIONS: A PRM with a formulation based on dilution of CRM470 was commutable with native clinical samples for 14 of 15 hsCRP methods that had acceptable precision. For those methods the use of PRM may contribute to improved harmonization of results for native clinical samples.

Interlaboratory comparison study of serum total testosterone [corrected] measurements performed by mass spectrometry methods.

BACKGROUND: Though mass spectrometry (MS) assays are increasingly used for routine clinical measurements of serum total testosterone (TT), information about the variability of results is limited. This study assessed the variability of TT measurement results from routine MS assays. METHODS: Twenty serum samples (12 females, 8 males) were analyzed on 2 days by seven high performance liquid chromatography (HPLC), and one gas chromatography (GC)-tandem mass spectrometry (HPLC-MS/MS, GC-MS/MS) assays. Two samples (male and female) were provided in five replicates to assess the within-run variability. Results were compared against those obtained at National Institute of Standards and Technology (NIST). The within- and between-laboratory variability was assessed for each sample. Comparisons to the NIST results were performed using bias plot and Deming regression analysis. RESULTS: The overall coefficient of variation of the results obtained with MS assays was <15%CV at >1.53 nmol/L and <34%CV at 0.3 nmol/L. The between-assay variability was the major contributor to the overall variability. The assay precision was the highest (<3%CV) with assays using liquid-liquid extraction for sample preparation or GC-MS/MS. The mean percent difference to the reference assay was 11%. The slopes of Deming regression analysis of the MS assays were between 0.903 and 1.138 (correlation coefficient: >0.996). TT concentrations for one assay were above the measurement range. CONCLUSIONS: The variability of TT measurement results among MS assays is substantially smaller than that reported for immunoassays. The type of sample preparation may affect assay precision. Standardizing assays can further reduce the variability of measurement results.

Introduction to standardization of laboratory results.

A fundamental goal of laboratory medicine is that laboratory results will be comparable or standardized and be independent of the laboratory where the testing was performed. Routine measurement procedures that are traceable to the same system of reference standards should produce numerical values for clinical samples that are comparable regardless of time, place, or laboratory generating the result. Standardization of laboratory measurements is key to providing accurate and reliable results from investigational studies and for optimal patient care.

CDC project on standardizing steroid hormone measurements.

Estradiol and testosterone measurements are widely used to assess steroid hormone status and to monitor stimulative, suppressive, or replacement therapy among children and adults of both sexes. Despite their common application, these measurements - particularly at low concentrations - show only limited comparability among assays, such as those observed for testosterone among women or for estradiol among postmenopausal women. This shortcoming hampers progress in research and in research translation. To overcome this, the Centers for Disease Control and Prevention, National Center for Environmental Health, Division of Laboratory Sciences (CDC/NCEH/DLS) initiated a project to standardize and to improve steroid hormone measurements. The project is a collaborative effort between institutions, organizations, and groups involved in estradiol and testosterone testing, test interpretation, and use. Specific activities are scheduled based on needs assessments conducted with the clinical, research, and public health communities. The initial focus of this standardization project is to improve analytical measurements through reference laboratory activities. As part of the project's translational activities, CDC/NCEH/DLS will work further with professional societies and organizations to improve pre- and postanalytical issues that affect results from these measurements and their interpretation.

Standardization of serum creatinine measurement: theory and practice.

Chronic kidney disease (CKD) is a major global public health problem. The best indicator of kidney function is considered to be the glomerular filtration rate (GFR), the rate that blood is filtered at the glomerulus. Currently, it is recommended that GFR be estimated using the estimating equation developed from the Modification of Diet in Renal Disease (MDRD) Study. To utilize the MDRD equation effectively requires reliable serum creatinine measurement. Understanding by laboratories world-wide of the importance of reliable serum creatinine measurements in GFR estimation and of factors that may affect creatinine measurement is critical to ongoing global public health efforts to increase the identification of patients with CKD. Serum creatinine assays must be properly calibrated and traceable to a high-order reference system in order to eliminate or significantly reduce variation among laboratories. If properly standardized world-wide, serum creatinine results can be used reliably to achieve universal implementation of GFR reporting as part of the global effort to diagnose and treat CKD.

Assessment of the relation between biomarkers for smoking and biomarkers for acrylamide exposure in humans.

Smoking is an important source of acrylamide exposure in the general population. We assessed the relationship between hemoglobin adducts of acrylamide (HbAA) and glycidamide (HbGA) as biomarkers of acrylamide exposure and plasma cotinine (PC) as biomarkers of tobacco smoke exposure in 94 men and 67 women. The median (5th-95th percentile) biomarker concentrations (pmol/g Hb) in the group of individuals with PC concentrations of 10 ng/mL [194 (87-403) and 107 (41-215) for HbAA and HbGA, respectively]. In individuals with PC concentrations of <1 ng/mL, HbAA and HbGA were similar to those observed in the group with PC values of 10 ng/mL. Although HbAA and HbGA could be categorized into distinguishable groups using PC concentration ranges commonly used to categorize presumed smokers and nonsmokers, no significant relationship was observed between these two biomarkers and PC within each group. The different exposure periods reflected by these biomarkers and the resulting different susceptibility to short-term variations in exposure patterns may in part explain these observations. The findings suggest that tobacco smoke exposure in individuals with PC values of <1 ng/mL has only a minimal effect on HbAA and HbGA.

Creation of a Universal Sample Bank for Determining the 99th Percentile for Cardiac Troponin Assays.

BACKGROUND: International guidelines authored and endorsed by professional societies of cardiology, emergency medicine, and laboratory medicine are unanimous that the cutoff concentration for establishing a diagnosis of acute myocardial infarction be set at the 99th percentile of a healthy population. The establishment of the actual 99th percentile value is assay- and sample-dependent and is influenced by the population of individuals selected for testing. We created a sample bank that will enable manufacturers of troponin assays a consistent comparison of the 99th percentile. METHODS: Participants were recruited from those attending the 2015 Annual Meeting of the AACC for the creation of a universal sample bank of apparently healthy individuals (free from uncontrolled diabetes, renal insufficiency, and heart disease). For those who met eligibility criteria and signed a written consent to participate, 60 mL blood was collected into 6 10-mL tubes each (2 serum, 3 heparin plasma, and 1 EDTA). Whole blood was tested for hemoglobin (Hb) A1c, and serum was tested for N-terminal pro-B-type natriuretic peptide (NT-proBNP) and creatinine. RESULTS: There were a total of 764 individuals who consented during the AACC Annual Meeting. After this initial enrollment, it was determined that there was an insufficient number of male participants recruited. Under the same protocol and consent, blood from 131 additional males was collected at the University of Maryland. Samples were centrifuged, and 240 µL aliquots of the 2 serum, 3 heparin plasma, and 1 EDTA tubes were frozen at 70 °C within 2 h of collection. The labeled samples were divided into boxes containing 1 aliquot from each individual. Sets of these samples were made available for purchase to manufacturers of cardiac troponin assays. Eighty-eight samples were excluded from the database for having a high NT-proBNP (>300 ng/L), low estimated glomerular filtration rate (eGFR) (<60 mL/min/1.73 m2), high Hb A1c (≥6.5%), or preanalytical sample issues and consenting/data issues. The final total was 808 individuals (402 females and 406 males; 60% Caucasian, 26% African or African American, 11% Asian or Pacific Islander, and 3% other). CONCLUSIONS: The creation of a bank of samples from healthy individuals enables a consistent comparison of the 99th percentile results from manufacturers of cardiac troponin assays.