Biomedical subjects

Aldy Kuypers

Publications and source records attributed to Aldy Kuypers.

4 recordsLinked to original sources

PubMed2006

Trueness verification and traceability assessment of results from commercial systems for measurement of six enzyme activities in serum: an international study in the EC4 framework of the Calibration 2000 project.

BACKGROUND: The in vitro diagnostics directive of the European Union requires traceability to higher order reference measurement procedures and materials for analytes in assuring the result trueness and comparability of laboratory measurements. Manufacturers must ensure that the systems they market are calibrated against available reference systems. Validation of metrologically traceable calibrations is, however, required. METHODS: A commutable serum-based material was analyzed in three reference laboratories and target values for six enzymes (ALT, AST, CK, GGT, LD, amylase) were assigned using IFCC reference measurement procedures. 70 laboratories in Germany, Italy, and The Netherlands measured the same enzymes in the material using procedures from six commercial companies. A system for maximum allowable error was developed from the biological variation model and the results of the various procedures were tested on their compliance to trueness and between-laboratory and within-laboratory variations relative to the maximum allowable. RESULTS: For ALT results were relatively good. >95% of laboratories using systems from Dade, Olympus, Ortho and Roche are expected to comply traceability within the biologically derived limits, and 94% respectively 89% from Abbott and Beckman. For AST and GGT only Dade respectively Olympus fully complied. For CK all companies showed significant bias. Nevertheless >95% of laboratories applying Abbott, Beckman and Roche systems will comply. Finally, LD and amylase measurements require significant improvement. Some manufacturers continue to sell on the European market assays giving results which are not traceable to the internationally accepted reference systems. CONCLUSIONS: The traceability of enzyme measurements obtained with routine procedures to internationally accepted IFCC reference systems is not yet satisfactorily accomplished in clinical practice.

Biomedical Research↗

PubMed2005

External Quality Assessment in The Netherlands: time to introduce commutable survey specimens. Lessons from the Dutch "Calibration 2000" project.

The performance of suitable secondary reference material for the use of trueness control of six routinely measured clinical enzymes in the Dutch External Quality Assessment (EQA) scheme is described. The reference material of choice was selected using the split-patient-sample between-field method (twin study) design as described in an earlier study of the Calibration 2000 project in The Netherlands. This material, which was proven to be commutable for all wet chemistry systems, was implemented as the national enzyme calibrator. It consisted of a cryo-protected lyophilised serum with additions of recombinant human enzymes. Various batches of the frozen version of this material without cryo-protection additive, called native EQA samples, were used in the general EQA scheme for performance evaluation. The results of Calibration 2000 calibrated and non-Calibration 2000 calibrated laboratories were compared for both the regular (spiked with non-human enzymes) and native EQA samples in terms of precision and bias with established reference method values for the native samples. The regular samples showed mean between-laboratory CV ranges for all six enzymes involved (low-high) of 5.5-10.3% for the non-calibrated users vs. 4.6-10.8% for the calibrated users. For the native samples these respective ranges were 5.2-9.9% vs. 2.2-4.9%. Without exception, the group of Calibration 2000 calibrated users showed the lowest bias against the reference method values. Regular EQA samples (spiked with non-human enzymes) showed poorer performance than native samples and are not suitable for accuracy assessment purposes, the main aim of EQA schemes. Native samples that are commutable should be used for trueness control in current EQA schemes.

Calibration↗

PubMed2002

Commutability assessment of potential reference materials using a multicenter split-patient-sample between-field-methods (twin-study) design: study within the framework of the Dutch project "Calibration 2000".

BACKGROUND: The Dutch project "Calibration 2000" aims at harmonization of laboratory results via calibration by development of commutable, matrix-based, secondary reference materials. An alternative approach to the NCCLS EP14 protocol for studying commutability of reference materials is presented, the "twin-study design", which in essence is a multicenter, split-patient-sample, between-field-methods protocol. METHODS: The study consisted of the simultaneous analysis of fresh patient sera and potential reference materials (PRMs) for HDL-cholesterol (HDL-C) by 86 laboratories forming 43 laboratory couples. Six subgroups of method combinations were formed. The patient sera were selected and interchanged by each laboratory couple. The PRMs consisted of three types: C37, prepared according to the NCCLS C37 protocol; Fro, frozen selectively pooled human serum; and Lyo, which was the same serum pool as Fro but lyophilized in the presence of sucrose. All PRMs were provided in three HDL-C concentrations. The regression line residuals for the PRMs were normalized by expressing them as multiples of the state-of-the-art within laboratory SD (SD(SA)). In addition, the extra contribution of each PRM to the total measurement uncertainty, CV(Netto), was calculated. RESULTS: Averaged over the three PRM concentrations, 1.6% of the C37 residuals were outside the 3 SD(SA) limit. For the Fro and Lyo PRMs, these values were 2.4% and 11.1%. CV(Netto) values for C37, Fro, and Lyo were 2.9%, 4.3%, and 5.3%, respectively. CONCLUSIONS: The present twin-study design, as a practical alternative to the NCCLS EP14 protocol, is a viable way of studying commutability characteristics of PRMs. The study suggests that the C37 PRMs are the best candidates for a future reference material.

Algorithms↗

PubMed2002

Selection, preparation, and characterization of commutable frozen human serum pools as potential secondary reference materials for lipid and apolipoprotein measurements: study within the framework of the Dutch project "Calibration 2000".

BACKGROUND: The Dutch project "Calibration 2000" aims at harmonization of laboratory results via calibration by development of matrix-based secondary reference materials. We considered the selection, preparation, and characterization of 34 potential reference materials (PRMs). METHODS: Sixteen PRMs were prepared either strictly according to the NCCLS C37-A protocol or in a less stringent and more convenient way. In addition, 18 commercial, so-called human serum-based calibrators or controls were purchased and tested. Lipoprotein integrity was evaluated by examining the physicochemical characteristics of the materials. Commutability of the PRMs was assessed in 86 Dutch clinical laboratories, using a multicenter split-patient-sample between-field-method (twin-study) design. Normalized residuals of the PRMs with respect to the patient regression lines were calculated; in addition, the extra contribution of each PRM to the total measurement uncertainty (CV(Netto)) was calculated. On the basis of these results, the most native PRM was selected to investigate its potential to reduce interlaboratory variation and to improve lipid and apolipoprotein standardization. RESULTS: In general, only the NCCLS C37-A-type materials displayed normalized residuals below the decision limit for commutability and had small CV(Netto) values ranging between 0 and 3.8%. This contrasts with the findings in regularly pooled frozen sera and lyophilized cryoprotected PRMs. In two subsequent external quality assessment surveys, the NCCLS type C37-A materials contributed to reducing the intermethod lipid and (apo)lipoprotein variation to approximately 2-4%. CONCLUSIONS: NCCLS C37-A materials have a strong potential as secondary reference materials, not only for cholesterol but also for HDL-cholesterol, LDL-cholesterol, triglyceride, and apolipoprotein measurements.

Apolipoprotein A-I↗