Interferences in coagulation tests--evaluation of the 570-nm method on the Dade Behring BCS analyser

The Dade Behring BCS is a coagulation analyser with optical reaction detection (standard 405 nm). The present study was conducted to evaluate measurement at 570 nm for analyses in interfering plasma samples. Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and D-dimer in normal (n=50), lipaemic (n=60), icteric (n=113), and haemolytic (n=58) samples were measured at 405 and 570 nm. As they are unaffected by the optical properties of the sample, the mechanical STAcompact analyser (Roche Diagnostics) and an ELISA technique were defined as the "comparison" methods. The percentage of valid PT results using the 570-nm method varied from 54% (lipaemic samples) to 97% (haemolytic samples). Valid aPTT measurements were found in 67% (lipaemic samples) up to 93% (icteric samples) of samples. Fibrinogen measurement revealed valid results in 58% (lipaemic samples) to 100% (haemolytic samples) of samples. The number of valid D-dimer results varied from 28% (lipaemic material) up to 100% (haemolytic material). Significant inter-method differences were found: aPTT in lipaemic (BCS 405 vs. 570 nm) and icteric samples (STAcompact vs. BCS 405 and 570 nm); fibrinogen in lipaemic (BCS 405 vs. 570 nm), icteric (BCS 405 vs. 570 nm; STAcompact vs. BCS 570 nm) and haemolytic samples (STAcompact vs. BCS 405 and 570 nm). Differences between the BCS 570-nm and the STAcompact methods were in most cases low and less pronounced than between the BCS 570- and 405-nm methods, making the BCS 570-nm method an alternative to measurement at 405 nm. Limitations have to be taken into account regarding lipaemic plasma.