Trueness and comparability assessment of widely used assays for 5 common enzymes and 3 electrolytes

An improved implementation of metrological traceability concepts is needed to benefit from standardization of laboratory results

Non-harmonization of laboratory results represents a concrete risk for patient safety. To avoid harms, it is agreed that measurements by in vitro diagnostic medical devices (IVD-MD) on clinical samples should be traceable to higher-order references and adjusted to give the same result. However, metrological traceability is not a formal claim and has to be correctly implemented, which in practice does not happen for a non-negligible number of measurands. Stakeholders, such as higher-order reference providers, IVD manufacturers, and External Quality Assessment organizers, have major responsibilities and should improve their contribution by unambiguously and rigorously applying what is described in the International Organization for Standardization 17511:2020 standard and other documents provided by the international scientific bodies, such as Joint Committee on Traceability in Laboratory Medicine and IFCC. For their part, laboratory professionals should take responsibility to abandon non-selective methods and move to IVD-MDs displaying proper selectivity, which is one of the indispensable prerequisites for the correct implementation of metrological traceability. The practicality of metrological traceability concepts is not impossible but relevant education and appropriate training of all involved stakeholders are essential to obtain the expected benefits in terms of standardization.

Alkaline Phosphatases: Biochemistry, Functions, and Measurement

Alkaline phosphatases (ALPs) are a group of isoenzymes, situated on the external layer of the cell membrane; they catalyze the hydrolysis of organic phosphate esters present in the extracellular space. Zinc and magnesium are significant co-factors for the biological activity of these enzymes. Although ALPs are available in various body tissues and have distinct physiochemical properties, they are true isoenzymes since they catalyze a similar reaction. In the liver, ALP is cytosolic and present in the canalicular membrane of the hepatocytes. ALPs are available in placenta, ileal mucosa, kidney, bone, and liver. However, most of the ALPs in serum (over 80%) are delivered from liver and bone and in more modest quantities from the intestines. Despite the fact that alkaline phosphatases are found in numerous tissues all through the body, their exact physiological function remains largely unknown.

EQA/PT scheme to improve the equivalence of enzymatic results between mutual recognition laboratories in Beijing

Background

To utilize the external quality assessment (EQA)/proficiency testing (PT) scheme to evaluate the equivalence of different clinical enzymatic measuring systems in Beijing.

Methods

The Beijing Center for Clinical Laboratory (BCCL) distributed three investigation samples to mutual recognition clinical laboratories in Beijing including alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ‐glutamyltransferase (GGT), creatine kinase (CK), and lactate dehydrogenase (LDH). These samples were derived from serum pools with values assigned by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) enzymatic reference measurement procedures (RMPs). Each laboratory performed duplicate tests of the samples. Then, the samples at level 1 were used to recalibrate individual measuring systems for repeating the tests. BCCL collected data for evaluation of their analytical quality.

Results

Before recalibration, the biases of ALT and AST tests were not traceable to the IFCC RMPs, and the bias pass rates of GGT, CK, and LDH tests were only 51.2%, 55.7%, and 48.6% respectively. After recalibration, the pass rates of ALT, AST, GGT, CK, and LDH increased to 95.1%, 82.9%, 95.1%, 97.1%, and 70.0% respectively. The EQA/PT also showed that after recalibration, more than 95% of laboratories met the optimum level specifications of the biological variation for ALT, AST, GGT, and CK tests and the desirable for LDH tests.

Conclusion

The enzymatic tests in Beijing need to be further standardized by category 1 or 2 EQA/PT scheme for mutual recognition between clinical laboratories. The criteria of biological variation are more relevant for determining the equivalence of clinical enzymatic tests.

Evaluation of serum electrolytes measurement through the 6-year trueness verification program in China

Objectives

The National Center for Clinical Laboratories (NCCL) in China initiated a serum electrolyte trueness verification (ETV) program in 2014 for measurement standardization.

Methods

Every year, two levels of fresh frozen commutable serum samples determined by inductively coupled plasma mass spectrometry (ICP-MS) reference methods were transported to participating clinical laboratories for the measurement of sodium, potassium, calcium and magnesium. Both samples were measured 15 times in 3 days, and the mean values and coefficient variations (CVs) were calculated from the results. The tolerance limits of trueness (bias), precision (CV) and accuracy (TE) based on the biological variation database were used as the evaluation criteria. The overall trend of the ETV program over 6 years was surveyed by calculating the pass rates of the participating laboratories. The mean bias, inter-laboratory CV, and TE of all laboratory results were analysed. Furthermore, homogeneous and heterogeneous systems were compared, and the bias and CV results of mainstream analysis systems were analysed.

Results

Pass rates of the three quality specifications increased, and the overall mean bias and inter-laboratory CVs decreased. The homogeneous system was superior to the heterogeneous system for calcium and magnesium measurements. For sodium, potassium, calcium and magnesium, the minimum bias corresponded to Hitachi, Siemens, Beckman AU and Roche, respectively. For inter-laboratory robust CVs, no obvious differences were observed between each peer group.

Conclusions

The commutable ETV materials assigned via reference methods can evaluate the accuracy and reproducibility of an individual laboratory and the calibration traceability and uniformity between laboratories for measurements.

Impacto de la introducción de un programa externo de categoría 1 en la vigilancia de la estandarización entre laboratorios clínicos en España

Introducción

El objetivo de este estudio es comprobar la evolución de las especificaciones de la prestación analítica (EPA) utilizadas en programas de garantía externa de la calidad (EQA) y el papel de un programa de categoría 1 en la vigilancia de la estandarización de la prestación de los laboratorios clínicos en España.

Métodos

Se ha revisado la bibliografía sobre tipos de especificaciones de la calidad usados en programas de otros países y se ha comprobado su evolución; se ha comparado el posible impacto de distintas EPA empleadas en ocho países en la toma de decisiones clínicas con tres ejemplos de magnitudes: sodio, tirotropina (TSH) y tiempo de tromboplastina parcial activado (TTPA).

Resultados

Se ha evidenciado la estandarización entre métodos analíticos comprobando si los resultados medios se desvían respecto al valor de referencia certificado del control dentro de las EPA derivadas de la variación biológica (VB). Las EPA usadas en EQA han evolucionado desde el estado del arte hacia la VB. Si se aplican los resultados que se aceptarían con algunas EPA se podrían producir decisiones clínicas erróneas.

Conclusiónes

En España, solo 2 de las 18 magnitudes biológicas estudiadas se pueden considerar bien estandarizadas. Sería necesaria una colaboración más estrecha entre los laboratorios y proveedores de sistemas analíticos para resolver las discrepancias.

Impact of implementing a category 1 external quality assurance scheme for monitoring harmonization of clinical laboratories in Spain

BACKGROUND

The objective of the present study was to examine the evolution of the analytical performance specifications (APS) used in External Quality Assurance (EQA) schemes, as well as the efficacy of a category 1 EQA scheme in monitoring the harmonization of clinical laboratory results in Spain.

METHODS

A review of the literature on the types of quality specifications used in schemes in other countries and their evolution was performed. In addition, a comparative analysis of the potential impact that different APS from eight countries had on clinical decision-making was made based on three measurands: sodium, thyroid-stimulating hormone (TSH), and activated partial thromboplastin time (aPTT).

RESULTS

Harmonization of analytical methods was demonstrated by assessing whether average results deviated from the certified reference value of control materials within the APS derived from biological variation (BV). The APS used in EQA have evolved from state-of-the-art models to BV. Poor clinical decision-making would occur if the results accepted by some APS were applied.

CONCLUSIONS

In Spain, only 2 of the 18 measurands studied are considered to be well harmonized. Closer collaboration between laboratories and analytical system providers would be required to resolve discrepancies.

Alanine Aminotransferase Results Differ by Analyzer Manufacturer in a National Integrated Health Setting, 2012-2017

CONTEXT.—

Disease guidelines specify universal alanine aminotransferase (ALT) thresholds for clinical decision-making, yet the effect of variability among ALT analyzers remains unclear.

OBJECTIVE.—

To compare ALT results from different analyzers from 2012-2017.

DESIGN.—

Veterans Health Administration (VHA) laboratories perform external ALT proficiency testing using standardized College of American Pathologists (CAP) samples in analyzers by 5 manufacturers. In this operational analysis, we evaluated 22 950 ALT values from 80 independent CAP samples tested at 223 laboratories. Using mixed effects modeling, we estimated the association between analyzer manufacturer and CAP outcome, adjusting for manufacturer, facility, and calendar year. We performed subgroup analyses on CAP samples with overall means near clinical guideline-specified thresholds, including less than 50 U/L (n = 10) and less than 35 U/L (n = 5).

RESULTS.—

The VHA used Abbott Laboratories (n = 3175; 14%), Beckman Coulter Diagnostics (n = 8723; 38%), Roche Diagnostics (n = 2595; 11%), Siemens Healthineers USA (n = 5713; 25%), and Vitros/Ortho Clinical Diagnostics (n = 2744; 12%) analyzers. The CAP samples (n = 80 samples, n = 22 950 tests) covered a wide range of mean ALT values (21-268 U/L). The average difference in mean ALT value per sample between the highest-reading and lowest-reading manufacturers was 15.4 U/L (SD = 1.8) for the 10 samples with mean ALT less than 50 U/L, and it was 10.4 U/L (SD = 3.6) overall (n = 80). In linear mixed effects modeling, we found statistically significant differences in ALT values between the different manufacturers in each year.

CONCLUSIONS.—

We found statistically and clinically meaningful differences between analyzers across the ALT spectrum in each year, including at ALT levels lower than 50 U/L and lower than 35 U/L. Universal ALT thresholds should be avoided as a trigger for clinical action until differences between analyzers can be resolved.

Evaluation of serum alkaline phosphatase measurement through the 4-year trueness verification program in China

Background Alkaline phosphatase (ALP) is critical for various diseases. The International Federation of Clinical Chemistry and Laboratory Medicine had recommended the new reference procedure in 2011, but many manufacturers did not trace results to the higher procedure. Since 2012, the National Center for Clinical Laboratories (NCCL) in China has organized the trueness verification program (TV) with commutable materials. The present study summarizes the 4-year TV program to give an overview of the measurement standardization for ALP results. Methods Commutable serum-based materials with different concentrations were prepared and sent to participating laboratories. The target values were assigned by the reference lab network. Results The analytical performance was evaluated according to three indexes: trueness (bias), imprecision (CV) and accuracy (total error [TE]). The number of participating laboratories increased from 115 in 2012 to 287 in 2016. The pass rates of precision for homogeneous and heterogeneous systems were all above 85% over the 4 years; however, the pass rates of bias were much lower (<50%). Among the homogeneous systems, Roche Cobas/Modular had an obvious negative bias, whereas the mean positive bias for Beckman AU was prominent. As to the heterogeneous systems, the pass rates of bias for Sichuan Maccura (57.1%-78.6%) were higher than Roche Cobas/Modular (4.4%-33.9%) and Beckman AU (35.7%-64.8%). Conclusions The PT/EQA program with commutable materials can be used to assess the trueness against target values assigned by reference procedures. For ALP, homogeneous systems did not perform better than heterogeneous systems. The bias for ALP performance was notable and was the main obstacle to its standardization in China.

The role of external quality assessment in the verification of in vitro medical diagnostics in the traceability era

Once an in-vitro diagnostic (IVD) measuring system has been marketed and introduced into daily practice, the possible sources of degradation of its performance are numerous. It is therefore essential to put in place a continuous post-market surveillance of the quality of performance of the IVD system and of the laboratories that perform measurements in clinical setting. The participation to external quality assessment (EQA) schemes that meet specific metrological criteria is central to the evaluation of performance of clinical laboratories in terms of standardization and clinical suitability of their measurements. In addition to the use of commutable materials, in this type of EQA it is necessary to assign values (and uncertainty) to them with reference procedures and to define and apply clinically permissible analytical performance specifications to substantiate the suitability of laboratory measurements in the clinical setting. Unfortunately, there are still few permanent EQA programs fully covering these requirements because some practical constraints, including technical and economic aspects, which limit their introduction. It is, however, clear that these issues should be quickly overcome, since EQA schemes are in a unique position to add substantial value to the practice of laboratory medicine, by identifying analytes that need improved harmonization and by stimulating and sustaining standardization initiatives that are needed to support clinical practice. Importantly, this will definitively help those manufacturers that produce superior products to demonstrate the superiority of those products and oblige end users (and consequently industry) to abandon assays with demonstrated insufficient quality.

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.

Analytical performance of 17 general chemistry analytes across countries and across manufacturers in the INPUtS project of EQA organizers in Italy, the Netherlands, Portugal, United Kingdom and Spain

Background:

Optimum patient care in relation to laboratory medicine is achieved when results of laboratory tests are equivalent, irrespective of the analytical platform used or the country where the laboratory is located. Standardization and harmonization minimize differences and the success of efforts to achieve this can be monitored with international category 1 external quality assessment (EQA) programs.

Methods:

An EQA project with commutable samples, targeted with reference measurement procedures (RMPs) was organized by EQA institutes in Italy, the Netherlands, Portugal, UK, and Spain. Results of 17 general chemistry analytes were evaluated across countries and across manufacturers according to performance specifications derived from biological variation (BV).

Results:

For K, uric acid, glucose, cholesterol and high-density density (HDL) cholesterol, the minimum performance specification was met in all countries and by all manufacturers. For Na, Cl, and Ca, the minimum performance specifications were met by none of the countries and manufacturers. For enzymes, the situation was complicated, as standardization of results of enzymes toward RMPs was still not achieved in 20% of the laboratories and questionable in the remaining 80%.

Conclusions:

The overall performance of the measurement of 17 general chemistry analytes in European medical laboratories met the minimum performance specifications. In this general picture, there were no significant differences per country and no significant differences per manufacturer. There were major differences between the analytes. There were six analytes for which the minimum quality specifications were not met and manufacturers should improve their performance for these analytes. Standardization of results of enzymes requires ongoing efforts.

Progress and impact of enzyme measurement standardization

International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) has established reference measurement procedures (RMPs) for the most popular enzymes. Manufacturers should assign values to commercial calibrators traceable to these RMPs to achieve equivalent results in clinical samples, independent of reagent kits, instruments, and laboratory where the measurement is carried out. The situation is, however, far from acceptable. Some manufacturers continue to market assays giving results that are not traceable to internationally accepted RMPs. Meanwhile, end-users often do not abandon assays with demonstrated insufficient quality. Of the enzyme measurements, creatine kinase (CK) is satisfactorily standardized and a substantial improvement in performance of marketed γ-glutamyltranspeptidase (GGT) assays has been demonstrated. Conversely, aminotransferase measurements often exceed the desirable analytical performance because of the lack of pyridoxal-5-phosphate addition in the commercial reagents. Measurements of lactate dehydrogenase (LDH), alkaline phosphatase (ALP), and α-amylase (AMY) still show major disagreement, suggesting the need for improvement in implementing traceability to higher-order references. This is mainly the result of using assays with different analytical selectivities for these enzymes. The definition by laboratory professionals of the clinically acceptable measurement uncertainty for each enzyme together with the adoption by EQAS of commutable materials and use of an evaluation approach based on trueness represent the way forward for reaching standardization in clinical enzymology.

Assessment of enzyme measurement procedures in China through a trueness verification program

BACKGROUND

Since 2003, the National Center for Clinical Laboratories (NCCL) has organized a network of reference laboratories and several survey programs to improve standardization in China.

METHODS

We analyzed the 2015 trueness verification program to assess the status of enzyme measurement standardization. Commutable serum-based materials were prepared and sent to 10 reference laboratories to assign target values for 2 enzymes (alanine aminotransferase-pyridoxal phosphate [ALT-pp] and γ-glutamyltransferase [GGT]) using IFCC reference measurement procedures.

RESULTS

Analytical performance was assessed for compliance to 3 indexes: trueness (bias), imprecision (CV), and accuracy (total error). Of the 250 participating laboratories, about half (≥124) used heterogeneous systems. More laboratories met the tolerance limit of imprecision than of trueness or accuracy. Except at the lowest concentration, the CV pass rates were >90% for the 2 enzymes. The optimal performance criterion derived from biological variation yielded pass rates for total error (ALT 77%, GGT 80%) that were higher than for bias (ALT 63%, GGT 73%).

CONCLUSIONS

PT/EQA results for commutable samples can be used to assess trueness against reference measurement procedures. Despite global and national standardization programs, bias remains a critical limitation of current enzyme measurement procedures in China.