Detection of protein C deficiency during oral anticoagulant therapy--use of the protein C:factor VII ratio.
Laboratory diagnosis of protein C deficiency is complicated by the fact that many patients referred for investigation are already being treated with oral anticoagulants. Protein C and factor VII have similar half lives and by using the protein C:factor VII ratio we hoped to be able to detect protein C deficiency in patients receiving oral anticoagulants. We have studied activity levels of protein C and factor VII to produce protein C:factor VII activity ratios in 105 patients receiving oral anticoagulants, 42 normal subjects, and nine patients with known inherited protein C deficiency. The mean ratios for these groups were 1.38, 1.12 and 0.63 respectively. In patients receiving oral anticoagulants, the protein C level showed a poor correlation with the international normalized ratio (INR) value. Reference ranges for protein C at different levels of anticoagulation were therefore considered unsuitable for the identification of inherited protein C deficiency. Five patients with inherited protein C deficiency were studied with and without oral anticoagulation; their protein C:factor VII ratios remained relatively unchanged, despite alterations in the level of the individual proteins. These results suggest that measurement of the protein C:factor VII ratio may help to identify patients with inherited protein C deficiency whilst on oral anticoagulants.
Haemophilia Centre, Thanet District General Hospital, Margate, Kent, UK.
D W
DW
Jones
I J
IJ
Mackie
M
M
Winter
M
M
Gallimore
S J
SJ
Machin
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000627:therapeutic use*; D005167:Factor VII / Q000032:analysis*; D005260:Female; D006801:Humans; D008297:Male; D011486:Protein C / Q000032:analysis; D020151:Protein C Deficiency; D012016:Reference Values
D000925:Anticoagulants; D011486:Protein C; D005167:Factor VII