Performance characteristics of a new synthetic APTT reagent

Performance characteristics of a totally synthetic activated partial thromb oplastin time (APTT) reagent, recently available commercially, were evaluat ed and compared with a rabbit-brain extracted reagent, We found that the sy nthetic reagent, Synthasil, returned significantly higher normal APTT value s than the brain-extracted reagent, Thrombosil. APTT ratios (APTT patients/ normal mean APTT), yielded by Synthasil were higher in the majority of pati ents receiving heparin therapy. Synthasil also returned longer APTT values than did Thrombosil on normal plasma spiked with heparin. On patients with lupus anti coagulants, APTTs assayed with Synthasil were generally longer t han with Thrombosil. However, the differences disappeared when APTT values were converted to ratios, Factors XII-, XI-, IX- and VIII-deficient plasmas supplemented with normal plasma to yield activities of 2-50%, generally ga ve longer APTTs with Synthasil than with Thrombosil. However, this was not always the case on plasmas from haemophilias A and B patients. No reduction in Synthasil activity was noted after the reagent had been left at 24 degr ees C for 28 days.