Validation of metrological traceability of the new generation of Abbott Alinity alkaline phosphatase assay.

OBJECTIVES: Recently, Abbott Diagnostics marketed a new generation of Alinity enzyme assays, introducing a multiparametric calibrator [Consolidated Chemistry Calibrator (ConCC)] in place of or in addition to factor-based calibrations. For alkaline phosphatase (ALP), both calibration options are offered, i.e., with ConCC (ALP2) and with an experimental calibration factor (ALP2F). Both options are declared traceable to the 2011 IFCC reference measurement procedure (RMP). Before to replace the old generation (ALP1) with the new one, we decided to validate the trueness of ALP2/ALP2F. METHODS: Three approaches were employed: (a) preliminary comparison on 48 native frozen serum samples with ALP1, of which traceability to RMP was previously successfully verified; (b) examination of three banked serum pools (BSP) with values assigned by RMP; (c) direct comparison with RMP on a set of 24 fresh serum samples. Bias estimation and regression studies were performed, and the standard measurement uncertainty associated with ALP measurements on clinical samples (uresult) was estimated and compared with established analytical performance specifications (APS). ConCC commutability was also assessed. RESULTS: A positive proportional bias was found with both ALP2 and ALP2F when compared to ALP1 and RMP. This positive bias was confirmed on BSP: in average, +13.1 % for ALP2 and +10.0 % for ALP2F, respectively. uresult were 13.28 % for ALP2 and 10.04 % for ALP2F, both not fulfilling the minimum APS of 4.0 %. Furthermore, ConCC was not commutable with clinical samples. CONCLUSIONS: Our results unearth problems in the correct implementation of traceability of Alinity ALP2/ALP2F, with the risk for the new assay to be unfit for clinical purposes.

Harmonization Status of Serum Ferritin Measurements and Implications for Use as Marker of Iron-Related Disorders.

BACKGROUND: Serum ferritin is considered a suitable biomarker of iron-related disorders. However, data about the comparability of results among commercial measuring systems (MSs) are contradictory. We performed an intercomparison study aimed at verifying the current interassay variability and its impact on clinical application of the test. Obtaining this information is vital because manufacturers continue to claim calibration alignment to different WHO preparations, which are not related to each other in terms of traceability. METHODS: Four widely used MSs were evaluated. The interassay agreement was verified using 39 human serum pools. The recovery of WHO International Standard (IS) 94/572 (the only reference material available at the time of the study) was evaluated, after assessing the material commutability. Finally, an approach for harmonizing ferritin results was proposed. RESULTS: Highly significant differences (P < 0.00001) among ferritin concentrations assayed by different MSs were detected and the interassay CV (median 22.9%; interquartile range 21.8-25.5) overlapped the desirable intermethod bias (24.6%). IS 94/572 was commutable for use only with Access and Centaur, with Access being the only MS correctly recovering its assigned value. Accordingly, we used regression data against Access to recalibrate MSs, indirectly aligning them to IS 94/572, with a substantial improvement in degree of harmonization and traceability to higher-order reference. CONCLUSIONS: The harmonization among evaluated ferritin MSs is far from optimal, with the implementation of traceability to different WHO ISs being a factor of confusion. A recalibration approach, however, would permit measurement harmonization, allowing the use of common decision thresholds.

Traceability validation of six enzyme measurements on the Abbott Alinity c analytical system.

Background Laboratory professionals should independently verify the correct implementation of metrological traceability of commercial measuring systems and determine if their performance is fit for purpose. We evaluated the trueness, uncertainty of measurements, and transferability of six clinically important enzyme measurements (alanine aminotransferase [ALT], alkaline phosphatase [ALP], aspartate aminotransferase [AST], creatine kinase [CK], γ-glutamyltransferase [γGT], and lactate dehydrogenase [LDH]) performed on the Abbott Alinity c analytical system. Methods Target values and associated uncertainties were assigned to three pools for each enzyme by using the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference measurement procedures (RMPs) and the pools were then measured on the Alinity system. Bias estimation and regression studies were performed, and the uncertainty associated with Alinity measurements was also estimated, using analytical performance specifications (APS) derived from biological variability of measurands as goals. Finally, to validate the transferability of the obtained results, a comparison study between two Alinity systems located in Milan, Italy, and Bydgoszcz, Poland, was carried out. Results Correct implementation of traceability to the IFCC RMPs and acceptable measurement uncertainty fulfilling desirable (ALP, AST, LDH) or optimal APS (ALT, CK, γGT) was verified for all evaluated enzymes. An optimal alignment between the two Alinity systems located in Milan and Bydgoszcz was also found for all enzyme measurements. Conclusions We confirmed that measurements of ALT, ALP, AST, CK, γGT, and LDH performed on the Alinity c analytical system are correctly standardized to the IFCC reference measurement systems and the system alignment is consistent between different platforms.

Trueness evaluation and verification of inter-assay agreement of serum folate measuring systems.

Background Definitive data to establish if the use of the WHO International Standard (IS) 03/178 as a common calibrator of commercial measuring systems (MSs) has improved the harmonization of serum total folate (tFOL) measurements to a clinically suitable level are lacking. Here, we report the results of an intercomparison study aimed to verify if the current inter-assay variability is acceptable for clinical application of tFOL testing. Methods After confirming their commutability, the IS 03/178 and National Institute for Standards and Technology SRM 3949 L1 were used for evaluating the correctness of traceability implementation by manufacturers and the MSs trueness, respectively. The inter-assay agreement was verified using 20 patient pools. The measurement uncertainty (U) of tFOL measurements on clinical samples was also estimated. An outcome-based model for defining desirable performance specifications for bias and imprecision for serum tFOL measurements was applied. Results The majority of evaluated MSs overestimated the WHO IS value of +5% or more with the risk to produce an unacceptably high number of false-negative results in clinical practice. The mean inter-assay CV on all pools and on those with tFOL values >3.0 µg/L (n = 15) was 12.5% and 7.1%, respectively. In neither case the goal of 3.0% was fulfilled. The residual bias resulted in an excessive U of tFOL measurement on clinical samples. Conclusions The implementation of traceability of tFOL MSs to the WHO IS 03/178 is currently inadequate, resulting in an inter-assay variability that does not permit the use of a common threshold for detecting folate deficiency.

Trueness Evaluation and Verification of Interassay Agreement of 11 Serum IgA Measuring Systems: Implications for Medical Decisions.

BACKGROUND: To identify an IgA deficiency, the availability of reliable IgA lower reference limits is essential, especially in pediatrics. In this study, we reported the results of an intercomparison study aimed to verify the status of standardization of IgA measurements using 11 commercially available measuring systems (MSs). METHODS: After confirming its commutability, the ERM-DA470k/IFCC reference material was used for the trueness evaluation of IgA MSs. Furthermore, the interassay agreement was verified using 18 patient pools. By combining the bias, if any, between the obtained mean of ERM-DA470k/IFCC and its target value and the mean imprecision of MSs with the uncertainty of respective calibrators, we also estimated the mean uncertainty (U) of IgA measurements on clinical samples. RESULTS: Although the majority of IgA MSs were sufficiently aligned with each other, the bias against the ERM-DA470k/IFCC target value was unacceptable in 55% of cases. This bias resulted in an excessive U of IgA measurement on clinical samples. Importantly, when the analysis focused on the lower IgA concentrations-typical of children-the situation worsened, with only 4 MSs showing good equivalence. CONCLUSIONS: Although the harmonization among most commercially available IgA MSs is good, the implementation of traceability to higher order references is inadequate, especially at concentrations ≤0.7 g/L. This analytical background information needs to be considered carefully when defining traceable reference intervals in the pediatric population.

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.

Verification of the harmonization of human epididymis protein 4 assays.

BACKGROUND: Serum human epididymis protein 4 (HE4) has gained relevance as an ovarian cancer (OC) biomarker and new automated methods have replaced the first released manual EIA by tracing results to it. We verified agreement and bias of automated methods vs. EIA as well as possible effects on patients' management. METHODS: One hundred and fifteen serum samples were measured by Abbott Architect i2000, Fujirebio Lumipulse G1200, Roche Modular E170, and Fujirebio EIA. Passing-Bablok regression was used to compare automated assays to EIA and agreement between methods was estimated by Lin's concordance correlation coefficient (CCC). The bias vs. EIA was estimated and compared to specifications derived from HE4 biological variation. RESULTS: Median (25th-75th percentiles) HE4 concentrations (pmol/L) were 84.5 (60.1-148.8) for EIA, 82.7 (50.3-153.9) for Abbott, 89.1 (55.2-154.9) for Roche, and 112.2 (67.8-194.2) for Fujirebio. Estimated regressions and agreements (95% confidence interval) were: Abbott=1.01(0.98-1.03) EIA-4.8(-7.5/-2.6), CCC=0.99(0.99-1.00); Roche=0.91(0.89-0.93) EIA+5.7(4.2/8.0), CCC=0.98(0.98-0.99); Fujirebio=1.20(1.17-1.24) EIA+ 2.4(-0.6/4.9), CCC=0.97(0.96-0.98). The average bias vs. EIA resulted within the desirable goal for Abbott [-3.3% (-6.1/-0.5)] and Roche [-0.2% (-3.0/2.5)]. However, while for Abbott the bias was constant and acceptable along the measurement concentration range, Roche bias increased up to -28% for HE4 values >250 pmol/L. Lumipulse showed a markedly positive bias [25.3% (21.8/28.8)]. CONCLUSIONS: Abbott and Roche assays exhibited a good comparability in the range of HE4 values around the previously recommended 140 pmol/L cut-off. For patient monitoring, however, the assay used for determining serial HE4 must not be changed as results from different systems in lower and higher concentration ranges can markedly differ.

Evaluation of the impact of standardization process on the quality of serum creatinine determination in Italian laboratories.

BACKGROUND: Creatinine determination in serum is a key indicator of kidney glomerular function. A reference measurement system for its standardization is available and virtually all IVD manufacturers have aligned their assays to this system. In this study, we verified the impact of these standardization efforts on the results of an Italian EQAS involving about 430 laboratories. METHOD: We considered data obtained during 2006, 2010 and 2011 schemes of EQAS Prolarit for control materials with target values assigned by a traceable method (enzymatic assay calibrated against the NIST SRM 967). RESULTS: The results showed a good alignment at concentrations ~170µmol/L, with 2011 results - except for one method group - well inside the desirable bias (±4%). At higher concentrations, whereas the bias was small in 2010, for some groups using alkaline-picrate (AP) methods it became significantly negative in 2011. The performance seems to worsen when measuring physiologic concentrations, where a significant positive bias (up to ~20%) is shown by most of the AP-based analytical systems. With few exceptions, no evident improvement in individual assay bias was noted from pre- (2006) to post-standardization (2011) periods. The enzymatic method groups were the only always presenting an acceptable bias at all creatinine concentrations, also showing the lowest between-laboratory variability. CONCLUSION: Our data seem to indicate that the standardization efforts are still having effects lower than expected. Even taking into consideration that some of the bias may derive from non commutability problems, most of the current "standardized" AP-based methods, at the lower creatinine concentrations, seem to present accuracy problems. This inaccuracy can adversely impact the estimation of GFR by equations and the evaluation of kidney function in pediatrics.