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a Address correspondence to this author at: De Baronie Hospital, Department of Clinical Chemistry, Langendijk 75, 4819 EV Breda, The Netherlands. Fax 31-76-5277-043; e-mail cobbaert{at}worldonline.nl
1
Lipid Reference Laboratory, University Hospital Rotterdam, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands, and, Hospital de Baronie, Department of Clinical Chemistry, Langendijk 75, 4819 EV Breda, The Netherlands
2
Roche Diagnostics Nederland B.V., Markerkant 13-10, 1314 AN Almere, The Netherlands
To the Editor:
Professionally set quality specifications are needed as major considerations in development of new reagents (1). Two years ago, the Dutch Lipid Reference Laboratory, a permanent international member of the CDC Cholesterol Reference Method Laboratory Network (2)(3), in collaboration with Roche Diagnostics Nederland B.V. (formerly Boehringer Almere, The Netherlands), began evaluating lot-to-lot differences of the new direct HDL-cholesterol (HDL-C) reagent from Kyowa Medex (cat. no. 1731157) and of the HDL-C/LDL-cholesterol cfas calibrator (cat. no. 1778501) before distribution on the Dutch market. To this end, a scaled down split-sample comparison protocol was used, essentially according to the design described in the HDL Cholesterol Method Evaluation Protocol for Manufacturers (4)(5). The accuracy platform was the CDC Designated Comparison Method (DCM) for HDL-C (2)(4); the test method was run on an Hitachi 911 analyzer (Boehringer Mannheim/Roche). A split-sample comparison was done with six specimens covering the HDL-C concentration range. All specimens were from individual donors. The matrix types investigated with the test method were serum and heparin plasma, whereas serum was used in combination with the DCM. Fresh specimens, intermittently stored at 4 °C, were analyzed with the test method, whereas frozen split sera were analyzed with the HDL-C DCM (5)(6). With the test method, all specimens were run in duplicate during 3 consecutive days for a total of 36 measurements (6 x 3 x 2 measurements); with the DCM, duplicate analyses were performed in one analytical run for a total of 12 measurements (6 x 2 measurements). Both test and reference data were produced in the Lipid Reference Laboratory in Rotterdam. Analytical performance was checked against the National Cholesterol Education Program guidelines (4). New lot combinations were acceptable when the total error criterion of 13% was met. Total error can be considered as an error budget that can be divided between imprecision and bias (4)(7).
During a 2-year period, 31 reagent/calibrator lot combinations for direct HDL-C were evaluated. For serum, the mean (± SD) results were as follows: mean bias (%), -1.6% ± 3.0%; mean absolute bias (%), 3.0% ± 1.9%; overall imprecision, 1.5% ± 0.7%; and total error, 5.5% ± 2.5%. For heparin plasma, the mean (± SD) results were as follows: mean bias (%), -2.7% ± 3.1%; mean absolute bias (%), 3.8% ± 2.1%; overall imprecision, 1.6% ± 0.7%; and total error, 6.2% ± 2.7%. In four reagent/calibrator lot combinations, the mean bias exceeded ± 5%, i.e., the excessive bias was related to one specific lot of calibrator in three combinations and to a specific reagent lot only once. In none of the combinations did the total error exceed 13%, the maximum total error being 11.1% for one serum matrix and 12.1% for the corresponding heparin plasma. Hence, all tested combinations were sold on the Dutch market. In the HDL-C reagent kit, a "Document of Comparison" issued by the Lipid Reference Laboratory Rotterdam is inserted, stating the overall analytical CV (%), the percentage of bias, and the percentage of total error for both matrices and for the tested reagent/calibrator lot numbers on a Hitachi 911 system.
It is concluded that the lot-to-lot differences of the direct HDL-C reagent and calibrator during the past 2 years were acceptable and in agreement with the 1998 National Cholesterol Education Program recommendations for HDL-C method performance (4). We have been assured that Roche will make further efforts to decrease the method bias to less than ± 5% in all combinations. The inserted Document of Comparison with the stated method bias and total error is objective evidence that should aid clinical chemists in the field to judge whether the quality of different lots of direct HDL-C reagent and calibrator meets recommended standards (4). In general, the results obtained for analytical performance characteristics should be compared to well-documented, objective quality specifications. We believe that assessment of the analytical performance by independent bodies across different sales lots should become part of (inter)national reagent release.
References
The following articles in journals at HighWire Press have cited this article:
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  C. Cobbaert, C. Weykamp, H. Baadenhuijsen, A. Kuypers, J. Lindemans, and R. Jansen 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" Clin. Chem., September 1, 2002; 48(9): 1526 - 1538. [Abstract] [Full Text] [PDF]
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