Evaluation of novel assays in clinical chemistry: Quantification of plasmatotal homocysteine

Background: There is a need for systematic evaluation of methods before the ir release to the market. We addressed this problem in novel homocysteine a ssays as part of an European Demonstration Project involving six centers in four countries. Methods: Two immunological methods for measurement of plasma total homocyst eine (P-tHcy), the fluorescence polarization immunoassay (FPIA) and the enz yme immunoassay (EIA), were compared with two comparison methods, HPLC and gas chromatography-mass spectrometry (GC-MS). All laboratories performed th e following procedures: (a) familiarization; (b) determination of linearity and precision by analyzing five plasma samples with interrelated concentra tions for 20 days; (c) correlation using patients' samples; and (d) assessm ent of long-term performance. Results: Both immunological methods were linear for P-tHcy between 5 and 45 mu mol/L. The intralaboratory imprecision (CV) was <5% for FPIA and <9% fo r EIA used with a sample processor. The bias was -2% to 3% for FPIA and 2-4 % for EIA used with a sample processor. Conclusions: The immunological methods provide results with little bias com pared with HPLC and GC-MS. The imprecision of the assays must be considered in the context of their intended use(s). (C) 2000 American Association for Clinical Chemistry.