Summary
Wide variations in procoagulant properties, lipid composition and ultrastructure of
five commonly used APTT methods have been demonstrated. Performance of the methods
with a range of coagulation abnormalities has been ranked. Most of the reagents obtained
a high score with one or more defects, but a low score with others. A consistent good
ranking throughout was only observed with one reagent.
The number of significant correlations between the reagents’ procoagulant activities
and lipid content confirms the view that the performance of an APTT method is largely
dependent upon its lipid composition. Marked differences in concentration and distribution
of phospholipids, fatty acids and neutral lipids were evident. The importance of the
concentration of phosphatidyl serine in regulating the procoagulant activity of an
APTT method has been demonstrated. Electron microscopy provides evidence of the contrasting
composition of the reagents from the more discrete uniform liposomes present in the
more reliable reagents, to more ill-defined components present in those reagents which
performed less well. The study highlights the need for standardisation of the APTT.
Key words
Activated partial thromboplastin time - Coagulation response - Lipid composition -
Ultrastructure
