Evaluierung des Homocystein-Immunoassays am Immulite 2500

The IMMULITE 2500 Homocysteine (Diagnostic Products Corporation, USA) is a new solid-phase, competitive chemiluminescent enzyme immunoassay with Logic Driven Incubation (LDI) capability for easy incorporation of STAT assays. The time-to-first-result for Homocysteine is 65 min with an incubation time of 2 x 30 min. Within-run imprecision (n=20) was determined for 3 different concentrations of patient samples and also for the specified control materials. The coefficients of variation (CVs) were 7,4%, 3,9% and 5,1% (patient samples, 3,8 µmol/l to 42,9 µmol/l) and 5,4% and 4,8% (control samples). Between-run imprecisions (n=12) showed CVs of 12,1%, 8,7% and 5,2% (patient samples) and 10,4% and 7,9% (control samples). Linearity was tested up to 45,5 µmol/l (r=0,996). High and low concentrated samples (n=16) were measured alternately without any carry over. For method comparison patient samples (n=120) were also measured at the ADVIA Centaur (Bayer) and with the method of HPLC. Data analysis showed good correlation coefficients of r=0,967 and r=0,954. Another method comparison between the new IMMULITE 2500, the ADVIA Centaur and the method of HPLC was made with hemodialysis patient samples (n=110, r=0,93 and r=0,96). During the evaluation period we found erroneous results in a few cases, which could not easily be accounted for. At the end, an unanticipated software issue was found if a sample or reagent arm error occurs just prior to the pre-treatment transfer step. The software problem caused the pipetting of an incorrect volume of pre-treated sample. As consequence, an urgent recall of IMMULITE 2500 Homocysteine was issued in October 2004. After the release of two new software versions within a short time we did not encounter any further problems.