Lipid composition of seven APTT reagents in relation to heparin sensitivity

The phospholipid content of different activated partial thromboplastin time (APTT) reagents was determined and compared to heparin sensitivity. The se ven reagents included were those most widely used amongst participants of t he U.K, National External Quality Assessment Scheme (NEQAS) at the time of study. Heparin sensitivity was assessed using the APTT ratios obtained by m ore than 300 NEQAS participants on five plasmas prepared from patients rece iving unfractionated heparin. The concentrations of three neutral lipids an d six phospholipids present in the seven APTT reagents were determined by h igh-performance thin-layer chromatography (HPTLC) and densitometry. Both th e concentrations and the relative percentages of individual phospholipid co mponents varied markedly between reagents. The total phospholipid concentra tion included a 12-fold range from 16 to 205 mu g/ml. Phosphatidylserine (P S) was completely lacking from one reagent prepared from vegetable material and ranged from 3 to 22 mu g/ml in the other six reagents containing extra cts from animal tissue. The concentration of phosphatidylcholine ranged fro m 3 to 109 mu g/ml. There was no demonstrable relationship between the conc entration of any individual lipid components and heparin sensitivity. Howev er, the relative percentage phospholipid composition was important since a lower % of PS or phosphatidylinositol (PI) correlated with increasing hepar in sensitivity.