Stanley F. Lo

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.

National Academy of Clinical Biochemistry laboratory medicine practice guidelines: follow-up testing for metabolic disease identified by expanded newborn screening using tandem mass spectrometry; executive summary.

BACKGROUND Almost all newborns in the US are screened at birth for multiple inborn errors of metabolism using tandem mass spectrometry. Screening tests are designed to be sufficiently sensitive so that cases are not missed. The NACB recognized a need for standard guidelines for laboratory confirmation of a positive newborn screen such that all babies would benefit from equal and optimal follow-up by confirmatory testing. METHODS A committee was formed to review available data pertaining to confirmatory testing. The committee evaluated previously published guidelines, published methodological and clinical studies, clinical case reports, and expert opinion to support optimal confirmatory testing. Grading was based on guidelines adopted from criteria derived from the US Preventive Services Task Force and on the strength of recommendations and the quality of the evidence. Three primary methods of analyte measurement were evaluated for confirmatory testing including measurement of amino acids, organic acids, and carnitine esters. The committee graded the evidence for diagnostic utility of each test for the screened conditions. RESULTS Ample data and experience were available to make strong recommendations for the practice of analyzing amino acids, organic acids, and acylcarnitines. Likewise, strong recommendations were made for the follow-up test menu for many disorders, particularly those with highest prevalence. Fewer data exist to determine the impact of newborn screening on patient outcomes in all but a few disorders. The guidelines also provide an assessment of developing technology that will fuel a refinement of current practice and ultimate expansion of the diseases detectable by tandem mass spectrometry. CONCLUSIONS Guidelines are provided for optimal follow-up testing for positive newborn screens using tandem mass spectrometry. The committee regards these tests as reliable and currently optimal for follow-up testing. .

State of the Art in Trueness and Interlaboratory Harmonization for 10 Analytes in General Clinical Chemistry

CONTEXT Harmonization and standardization of results among different clinical laboratories is necessary for clinical practice guidelines to be established. OBJECTIVE To evaluate the state of the art in measuring 10 routine chemistry analytes. DESIGN A specimen prepared as off-the-clot pooled sera and 4 conventionally prepared specimens were sent to participants in the College of American Pathologists Chemistry Survey. Analyte concentrations were assigned by reference measurement procedures. PARTICIPANTS Approximately 6000 clinical laboratories. RESULTS For glucose, iron, potassium, and uric acid, more than 87.5% of peer groups meet the desirable bias goals based on biologic variability criteria. The remaining 6 analytes had less than 52% of peer groups that met the desirable bias criteria. CONCLUSIONS Routine measurement procedures for some analytes had acceptable traceability to reference systems. Conventionally prepared proficiency testing specimens were not adequately commutable with a fresh frozen specimen to be used to evaluate trueness of methods compared with a reference measurement procedure.

Laboratory Performance in Neonatal Bilirubin Testing Using Commutable Specimens: A Progress Report on a College of American Pathologists Study

CONTEXT In 2003 the Chemistry Resource Committee of the College of American Pathologists introduced a commutable specimen in the Neonatal Bilirubin Surveys. This specimen was intended to help evaluate all bilirubin methods. OBJECTIVE To evaluate the effect of commutable specimens on the performance of selected clinical analyzers in measuring neonatal bilirubin from 2003 through 2006. DESIGN A human serum-based specimen enriched with unconjugated bilirubin in human serum has been included since 2003 in the Neonatal Bilirubin Surveys. The bilirubin values of these specimens were determined by the reference method and used to evaluate results reported by various chemistry analyzers. RESULTS Coefficients of variation for College of American Pathologists All Data ranged from 4.9% to 6.2% for the Neonatal Bilirubin Survey. However, coefficients of variation for the 4 major instrument groups (Dimension, Olympus, Synchron, and Vitros), which report 65% of all results, varied from 2% to 3%. College of American Pathologists All Data mean bilirubin values were within 0.46 mg/dL (7.8 micromol/L) of the reference method mean in 2003; in subsequent years these differences became larger, peaking at 1.87 mg/dL (32 micromol/L) in 2005. CONCLUSIONS The large systematic error of bilirubin measurements is due primarily to failure of instrument manufacturers to produce reliable bilirubin calibrators. Primary calibrators should consist of human serum enriched with unconjugated bilirubin. Bilirubin values must be assigned by the reference method, the performance and robustness of which are reported in this article. Secondary calibrators distributed to users must be traceable to primary calibrators.

The status of bilirubin measurements in U.S. laboratories: why is accuracy elusive?

In 2003, the Chemistry Resource Committee of the College of American Pathologists introduced a new specimen in the Neonatal Bilirubin Survey. The specimen, consisting of human serum enriched with unconjugated bilirubin and thus resembling a clinical specimen, brought about an improvement in the accuracy of the measurement of bilirubin by laboratories participating in the Neonatal Bilirubin Survey. There was also an improvement in the specificity of methods measuring direct bilirubin. However, persisting inaccuracies and variability in laboratory performance have been traced to calibrators consisting of bovine serum spiked with unconjugated bilirubin and ditaurobilirubin; bovine serum causes underestimation of both bilirubins by 8 major chemical analyzers. To eradicate inaccuracy calibrators and Survey specimens should be made in human instead of bovine serum.

Bilirubin proficiency testing using specimens containing unconjugated bilirubin and human serum: results of a College of American Pathologists study.

CONTEXT Specimens of the College of American Pathologists Neonatal Bilirubin and Chemistry surveys are inadequate for evaluating the performance of clinical laboratories in measuring serum bilirubin because they exhibit strong matrix interference. Recently published data indicate that at least 1 major clinical analyzer provided inaccurate bilirubin values for Neonatal Bilirubin Survey specimens. The composition of the specimens, bovine serum enriched with ditaurobilirubin, was responsible for the erroneous results. OBJECTIVE This article evaluates the performance of major clinical analyzers using a survey specimen free of matrix interference. DESIGN A human serum-based specimen enriched solely with unconjugated bilirubin was included in the 2003 Neonatal Bilirubin and Chemistry surveys. Its bilirubin concentration (19.4 mg/dL [332 micromol/L]) was determined by the reference method for total bilirubin. RESULTS The coefficients of variation for the 4 major clinical analyzers (Dimension, Hitachi, Synchron, and Vitros) ranged from 1.9% to 3.7%. When compared to the bilirubin value measured by the reference method, mean bilirubin values of the 4 major clinical analyzers and College of American Pathologists (CAP) All Data (which refers to the grand mean and overall coefficient of variation of all method principles, all instruments according to CAP terminology) ranged from -3.5% to 5.1%. Direct bilirubin results from most field methods showed good specificity overall. CONCLUSION Human serum-based survey specimens, having their bilirubin concentrations determined by the reference method, should be included as frequently as feasible in the Neonatal Bilirubin Survey. Such specimens may be used by instrument manufacturers as standards for calibrating bilirubin methods and for assigning values to calibrators provided to instrument users. A substantial improvement in bilirubin measurements due to the reduction of systematic error is expected.

Severe hypercholesterolemia mediated by lipoprotein X in a pediatric patient with chronic graft-versus-host disease of the liver

We describe a case of extreme hypercholesterolemia, mediated by lipoprotein X, in a 12‐year‐old Caucasian female who underwent an unrelated allogenic bone marrow transplant for relapsed acute myelocytic leukemia (AML). Her post‐transplant course was complicated by severe chronic graft‐versus‐host disease (GVHD) of the liver. Previously normal serum cholesterol and triglycerides rose to 1,122 mg/dl (29.0 mmol/L) and 1,100 mg/dl (12.4 mmol/L), respectively. Serum cholesterol appeared to be dominantly carried by lipoprotein X. Intra‐hepatic cholestasis leading to reflux of bile lipoproteins into the blood stream and subsequent formation of lipoprotein X appears to be the mechanism underlying this phenomenon. Pediatr Blood Cancer 2008;50:1280–1281.

BiliChek transcutaneous bilirubin meter overestimates serum bilirubin as measured by the Doumas reference method

OBJECTIVES To determine the relationship between BiliChek TcB (Respironics, Marietta GA) and Doumas reference serum or plasma total bilirubin (TSB). DESIGN AND METHODS Pooled samples with values assigned by the Doumas reference method were used to establish the relationship between a local laboratory and reference Doumas TSB. We then established the relationship between TcB and TSB in the 3 months before and after reassignment of calibrator setpoints undertaken to match the local laboratory to Doumas reference bilirubin values. RESULTS Before calibrator setpoint reassignment TSB as measured in our laboratory overestimated Doumas reference bilirubin. After calibrator adjustment laboratory TSB was within 1.7-6.8 micromol/L (0.1-0.4 mg/dL) of Doumas reference values. Mean bias between BiliChek TcB and TSB was 42.8+/-22.2 micromol/L (2.5+/-1.3mg/dL) (n=94) before and 49.6+/-22.2 micromol/L (2.9+/-1.3mg/dL) (n=115) after calibration adjustment. CONCLUSIONS BiliChek TcB significantly overestimates TSB as measured by the Doumas reference method.

Interlaboratory comparison of the Doumas bilirubin reference method.

OBJECTIVES To assess the performance of the Doumas bilirubin reference method. DESIGN AND METHODS Ring trails using pooled patient specimens, a calibrator and human sera enriched with unconjugated bilirubin were analyzed in five laboratories using the Doumas bilirubin reference method. RESULTS The coefficient of variation for the linear measurement range between laboratories ranged from 1-3%. CONCLUSIONS The Doumas bilirubin reference method is robust and reproducible. Bilirubin results using this method may be used in the development of more accurate and reliable calibrators.

Laboratory Performance in Albumin and Total Protein Measurement Using a Commutable Specimen: Results of a College of American Pathologists Study

CONTEXT Discrepant results for serum constituents were observed among peer groups in the College of American Pathologists Comprehensive Chemistry Survey. OBJECTIVES To assess the performance of serum albumin and total protein measurement procedures and to evaluate the commutability of the conventional survey specimens. DESIGN A fresh frozen, off-the-clot serum sample was included along with 4 conventional survey specimens. The fresh frozen, off-the-clot serum sample was prepared in a manner expected to confer commutability with native clinical samples. RESULTS For the fresh frozen, off-the-clot serum sample, the mean values for 17 peer-groups were -0.07 to 0.32 g/dL from the bromocresol green albumin designated comparison method, whereas 4 VITROS (Ortho Clinical Diagnostics, Rochester, New York) peer groups differed by -0.29 to -0.37 g/dL (15 of 21 differences [71%] had P < .001). For bromocresol purple albumin methods, the mean differences from the designated comparison method from 8 peer groups were 0.25 to 0.47 g/dL (all had P < .001). For total protein methods, 23 peer group mean values were -0.07 to 0.15 g/dL from the reference measurement procedure (12 of 24 [50%] had P < .001). The Beckman (Fullerton, California) Synchron LX20 had a bias of -0.30 g/dL (P <.001). The commutability of the conventional specimens was acceptable for 23 of 24 bromocresol green method-material combinations (96%) and 13 of 16 bromocresol purple albumin method-material combinations (81%). All (100%) of the 36 method-material combinations had acceptable commutability for total protein. CONCLUSIONS One (2.2%) of the instrument systems (Synchron) using bromocresol green and none (0%) of the instrument systems using bromocresol purple had satisfactory total-error performance for albumin measurement. Differences in results between bromocresol green and bromocresol purple methods precluded using common reference intervals for interpreting results for serum albumin. Eight of 9 instrument systems (86.5%) had satisfactory total-error performance for total protein measurement.