Determination of coagulation factor VIII activity by a chromogenic substrate method on STA, an automated coagulation analyzer

This study was aimed at evaluating the performance of a chromogenic factor VIII assay on STA, an automated coagulation analyzer. Additionally, a corre lation study was conducted with an aPTT-based one-stage factor VIII clottin g assay. Throughout the study the performance of the chromogenic assay was tested in two ranges of factor VIII activity: al high range with activity b etween 20% and 150% and a low range with activity below 20%. Inter-assay co efficient of variation ranged from 1.9% to 8.9% and intra-assay coefficient of variation from 0.5% to 11.4%, depending on factor VIII concentration. D ay-today reproducibility was tested over a 5-day period; between-day imprec ision ranged from 7.1% to 9.4%. The chromogenic factor VIII assay showed a good correlation with the clotting assay ire both ranges. The correlation c oefficients were 0.924 and 0.792 for the high and low range, respectively. A statistically significant difference in mean values was observed in the h igh range (p < 0.0001). Comparison between the chromogenic assay on STA ver sus on microplates showed a high correlation (0.991), which was highly sign ificant (p < 0.0001). In conclusion, the chromogenic assay for factor VIII on STA shows good analytical performance. It correlates well with the one-s tage factor VIII clotting assay, although significant differences between i ndividual samples occur. Probably these are partly related to differences i n measurement principle and standardization. Altogether, this precise and r apid assay is suitable for determination of factor VIII by an automated pro cedure.