Chromogenic substrates for activated partial thromboplastin time testing: are they worth using?

In hemostasis testing the development of chromogenic substrates provides an alternative to the traditional methods based on the detection of forming clots. The new technology has often replaced the clotting tests, especially in the area of single clotting factor and inhibitor assay, less frequently for global screening tests. We report studies of the validity and clinical application of two reagents for activated partial thromboplastin time (APTT) testing with chromogenic substrates in comparison with the conventional clotting method. Congenital deficiencies of the intrinsic coagulation pathway, other than hypo- and dysfibrinogenemia detected by chromogenic APTT, agreed with those detected by the clotting APTT. The results with the two methods for plasma under heparin treatment suggest a lesser responsiveness of the chromogenic methods to heparinization. The chromogenic methods demonstrated the presence of the lupus anticoagulant in the majority of tested samples of known lupus subjects, but with a lower responsiveness than the clotting method. In conclusion, we found chromogenic APTT suitable for hemostasis testing because it generally gives the same information as the conventional clotting method with the exception of heparin monitoring and lupus anticoagulant detection, where an improved sensitivity would be desirable.