Laboratory Medicine Reference Research Articles

Research and application of laboratory medicine reference measurement system

Research and application of laboratory medicine reference measurement system

Standardization of clinical enzyme analysis using frozen human serum pools with values assigned by the International Federation of Clinical Chemistry and Laboratory Medicine reference measurement procedures

Variation in clinical enzyme analysis, particularly across different measuring systems and laboratories, represents a critical but long-lasting problem in diagnosis. Calibrators with traceability and commutability are imminently needed to harmonize analysis in laboratory medicine. Fresh frozen human serum pools were assigned values for alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyltransferase (GGT), creatine kinase (CK) and lactate dehydrogenase (LDH) by six laboratories with established International Federation of Clinical Chemistry and Laboratory Medicine reference measurement procedures. These serum pools were then used across 76 laboratories as a calibrator in the analysis of five enzymes. Bias and imprecision in the measurement of the five enzymes tested were significantly reduced by using the value-assigned serum in analytical systems with open and single-point calibration. The median (interquartile range) of the relative biases of ALT, AST, GGT, CK and LDH were 2.0% (0.6–3.4%), 0.8% (−0.8–2.3%), 1.0% (−0.5–2.0%), 0.2% (−0.3–1.0%) and 0.2% (−0.9–1.1%), respectively. Before calibration, the interlaboratory coefficients of variation (CVs) in the analysis of patient serum samples were 8.0–8.2%, 7.3–8.5%, 8.1–8.7%, 5.1–5.9% and 5.8–6.4% for ALT, AST, GGT, CK and LDH, respectively; after calibration, the CVs decreased to 2.7–3.3%, 3.0–3.6%, 1.6–2.1%, 1.8–1.9% and 3.3–3.5%, respectively. The results suggest that the use of fresh frozen serum pools significantly improved the comparability of test results in analytical systems with open and single-point calibration.

Progress in the application of mass spectrometry in reference measurement procedures

The establishment of laboratory medicine reference system is an important way for routine detection results to achieve traceability. The complete reference system consists of reference measurement procedures, reference materials and reference laboratories. The reference measurement procedure is usually characterized by a thorough study with a small measurement uncertainty. Based on the advantages of high specificity and high sensitivity in quantitative analysis, mass spectrometry plays an important role in the research of the reference measurement procedures in laboratory medicine. In the past 40 years, mass spectrometry technology has been more and more widely applied in medicine, electrolytes, metabolites and substrates, non-electrolyte metals, non-peptide hormones, protein and vitamin. It provides a powerful guarantee for the precise detection of these well-defined measureds.(Chin J Lab Med, 2017, 40: 823-828) Key words: Reference values; Reference standards; Mass spectrometry

National and international initiatives and approaches for the establishment of reference intervals in pediatric laboratory medicine

Abstract Thoroughly validated laboratory medicine reference intervals for children of all ages groups have been published increasingly during the last years. The aim of this review is to present a number of these studies and the various approaches to the generation of reference intervals. Population-based data obtained in large cohorts of healthy children in Germany, Northern Europe, North America, and selected other countries as well as patient-derived data collected in many areas of the world are discussed. Additionally, special research aspects such as reference intervals for preterm neonates, preanalytical issues, intraindividual variation of analytes, or follow-up studies that are covered in many of these studies are presented.

Glycated hemoglobin a1c as a modern biochemical marker of glucose regulation

GLYCATED HEMOGLOBIN STRUCTURE AND SYNTHESIS OF MOLECULE: Glycated hemoglobin A1c, the major fraction of glycated hemoglobin, is formed by irreversible nonenzymatic glycation. Its concentration depends only on the life span of red blood cells and blood glucose levels. CLINICAL SIGNIFICANCE OF GLYCATED HEMOGLOBIN A1c: It is the key parameter for monitoring the regulation of diabetes and for assessing the risk of microvascular complications. It is a diagnostic criterion for diabetes as well. Its concentration reflects the average value of blood glucose over the last two to three months. The estimated average glucose, a new parameter which facilitates the patient's self-monitoring of diabetes, can be calculated from its value. METHODS FOR DETERMINING GLYCATED HEMOGLOBIN A1c AND THEIR STANDARDIZATION: Immunoassay and ion-exchange chromatography are commonly used methods for the glycated hemoglobin determination in routine laboratory practice. The advantage of immunoassay is that there is no need for the sample pre-treatment in order to eliminate unstable glycated hemoglobin A1c intermediary forms, and the possibility of false positive results is lower. The current program of standardization requires traceability to the International Federation of Clinical Chemistry and Laboratory Medicine reference method. REPORTING AND INTERPRETATION OF RESULTS OF GLYCATED HEMOGLOBIN A1c DETERMINATION: Glycated Hemoglobin A1c can be reported as % or as mmol/mol. In our country, it is recommended to use the International Federation of Clinical Chemistry and Laboratory Medicine units (mmol/mol). When interpreting the results, the potential causes of falsely high or low values must always be taken into consideration. Periodic determinations of glycated hemoglobin A1c are recommended for monitoring of diabetes regulation. Additionally, the determination is recommended for the diagnosis of diabetes. The target value for the prevention of microvascular complications is < 7% and the diagnostic criterion for diabetes is 6.5%.

Glycated hemoglobin (HbA1c) measurement in frozen whole blood depends on baseline values of fresh samples

Glycated hemoglobin (HbA1c) has been recently adopted as a diagnostic marker of type 2 diabetes. However, its usage is currently limited to fresh blood samples. To allow retrospective HbA1c measurement in blood banks developed in large epidemic studies, here, we contribute to validate HbA1c assessment in frozen versus fresh blood samples from a cohort of diabetic/nondiabetic adult subjects. HbA1c was measured by HPLC in 237 fresh whole blood samples and on the same samples after a 12-month storage and a further 6-month-refrozen storage. Mean HbA1c ± SD in fresh, frozen, and refrozen samples was 6.9 ± 1.2, 6.6 ± 1.1, and 6.4 ± 1.0% for the Diabetes Control and Complications Trial and 52 ± 13, 49 ± 12, and 46 ± 11 mmol/mol for the International Federation of Clinical Chemistry and Laboratory Medicine reference, respectively. A significant correlation was found between fresh/frozen and fresh/refrozen (R = 0.994 and 0.993, P < 0.001) samples. HbA1c relative error ratio (%RER) between frozen/refrozen and fresh samples significantly correlated with HbA1c and depended on fresh value range, increasing in the five HbA1c classes (<6.0, 6.0-6.5, 6.5-7, 7-8, ≥8%, corresponding to <42, 42-48, 48-53, 53-64, ≥64 mmol/mol, P < 0.001). In particular, the 6.5% (48 mmol/mol) HbA1c diagnostic cutoff of fresh samples identified two classes reflecting significant differences in %RER (2.8 ± 2.0 and 3.3 ± 1.7; P < 0.05) between frozen and fresh samples. In conclusion, our results demonstrate a high correlation between data from fresh and frozen samples, with a very limited %RER between the two measurements, which increases with baseline HbA1c levels. Accordingly, when analyzing biobank frozen specimens for diagnostic purpose, the effect of the HbA1c range should be taken into account.

Lipoprotein(a) levels, apo(a) isoform size, and coronary heart disease risk in the Framingham Offspring Study

The aim of this study was to assess the independent contributions of plasma levels of lipoprotein(a) (Lp(a)), Lp(a) cholesterol, and of apo(a) isoform size to prospective coronary heart disease (CHD) risk. Plasma Lp(a) and Lp(a) cholesterol levels, and apo(a) isoform size were measured at examination cycle 5 in subjects participating in the Framingham Offspring Study who were free of CHD. After a mean follow-up of 12.3 years, 98 men and 47 women developed new CHD events. In multivariate analysis, the hazard ratio of CHD was approximately two-fold greater in men in the upper tertile of plasma Lp(a) levels, relative to those in the bottom tertile (P < 0.002). The apo(a) isoform size contributed only modestly to the association between Lp(a) and CHD and was not an independent predictor of CHD. In multivariate analysis, Lp(a) cholesterol was not significantly associated with CHD risk in men. In women, no association between Lp(a) and CHD risk was observed. Elevated plasma Lp(a) levels are a significant and independent predictor of CHD risk in men. The assessment of apo(a) isoform size in this cohort does not add significant information about CHD risk. In addition, the cholesterol content in Lp(a) is not a significant predictor of CHD risk.

Introducing the new laboratory standard of HbA1cdetermination in Hungary

A new laboratory standard, specific for HbA1c was prepared by the International Federation of Clinical Chemistry and Laboratory Medicine. Consequently, manufacturers will supply their calibrators with the International Federation of Clinical Chemistry and Laboratory Medicine standard. Laboratories in Hungary switch to this new method in April 1, 2011. After this date, results of HbA1c measurements will be reported in International Federation of Clinical Chemistry and Laboratory Medicine units (mmol/mol) and in the derived National Glycohemoglobin Standardization Program units (%) calculated by master equation from the International Federation of Clinical Chemistry and Laboratory Medicine/National Glycohemoglobin Standardization Program methods. Using the new standardization the HbA1c measurements will be traceable to the International Federation of Clinical Chemistry and Laboratory Medicine reference method and interlaboratory comparisons will be possible.

Application of five frozen human-pooled serum samples assigned by the International Federation of Clinical Chemistry and Laboratory Medicine reference procedure in a traceability investigation of γ-glutamyltransferase catalytic concentration measurements in China

The in vitro directive of the European Union requires traceability to the international recommended reference procedures. The application of the reference procedures is necessary in order to evaluate the accuracy of gamma-glutamyltransferase (GGT) assays of routine measurement systems in China. Five frozen patient-pooled serum samples were assigned values by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference procedure in order to evaluate the traceability of the results of GGT catalytic activity from six homogeneous systems. One of the serum samples was used to calibrate seven non-homogeneous systems. All of the homogeneous systems, except the Dade system (Dade Bering Inc, IL, USA), achieved traceability within the measurement range. The Roche and Hitachi systems were better than the other systems. After calibration, the variance of the non-homogeneous systems decreased dramatically from between 14.50% and 25.23% to between 1.25% and 3.09% and the bias decreased from between -11.4% and -4.1% to between 0.5% and 3.5%. Manufacturers in China should ensure that their calibration systems correspond to the IFCC reference procedures. Fresh frozen pooled patient serum assigned by reference laboratories can be used to calibrate non-homogeneous systems in order to achieve traceability.

Metrological traceability is not always a straight line

The two most important concepts in metrology are certainly “traceability to standards” and “measurement uncertainty evaluation”. So far the questions related to these concepts have been reasonably solved in the metrology of “classical quantities”, but for the introduction of metrological concepts in new fields, such as chemistry and biology, a lot of problems remain and must be solved in order to support international arrangements. In this presentation, the authors want to develop the strategy implemented at Laboratoire national de metrologie et d’essais (LNE) in metrology in chemistry and biology. The strategy is based on: (1) pure solutions for calibration of analytical instruments, (2) use of certified reference materials (matrix reference materials), and (3) participation to proficiency testing schemes. Examples will be presented in organic and inorganic chemistry. For laboratory medicine, proficiency testing providers play an important role in the organization of External Quality Assessment Schemes. For the time being, the reference value or the assigned value of the comparison is calculated with the results obtained by the participants. This assigned value is not often traceable to SI units. One of the methods suggested by LNE is to ensure the metrological traceability to SI units of the assigned value for the more critical quantities carried on analytes by implementing the Joint committee for traceability in laboratory medicine reference methods.

Evaluation of serum gamma-glutamyltransferase assays by using the International Federation of Clinical Chemistry and Laboratory Medicine reference method

Objective To evaluate the measurement accuracy of serum gamma-glutamyltransferase (GGT) assays manufactured in China. Methods The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference method for GGT was set up and, after verification, was used to evaluate the performance of routine assay systems made in China. The evaluation was performed twice before and after a calibration by a common serum calibrator. Results For the reference measurement, the within run and total CVs were all less than 1%. The biases with the target values of IFCC External Quality Assessment Scheme for Reference Laboratories (RELA) were all within the limit of equivalence. Before a calibration with a common calibrator, the largest biases of results of GGT of the routine tasting systems compared with reference method at three medical decide levels were -47.53%, -34.11% and -30.07% respectively, and the averaged biases were 14.53% ,12.88% and 12.48%. After calibrating by fresh serum calibrator,the largest biases were reduced to - 17.63%, -5.88% and -4.08% ,the averaged biases were reduced to 7.50%, 2.70% and 1.87%. Conclusion The performance of GGT measurements can be effectively improved by using a common fresh serum calibrator that has a value assigned with the reference method. Key words: gamma-Glutamyltransferase; Reference values; Indicators and reagents; Calibration