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.