Comparison of Activated Partial Thromboplastin Reagents

Five commercial reagents and one noncommercial reagent for determining activated partial thromboplastin times were tested for reproducibility of results and ability to detect abnormalities of the intrinsic coagulation system. The sensitivity of the reagents to factors VIII and IX varied markedly; two reagents were so insensitive to factor IX that results obtained were misleading. Reproducibility of results with all reagents tested was satisfactory, although wide inter-reagent variability in results was noted.