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We investigated sensitivity to activated protein C (APC) in 43 men, 42 women not using oral contraceptives (OC) and 38 women using OC containing 30.0-37.5 micrograms ethinyl estradiol. A commercially available kit was used. Men were more sensitive to APC as compared with women not using OC (p < 0.005), but this difference seems not to be of clinical importance. Women using OC showed to be significantly less sensitive to APC, reflected by a lower APC-ratio, as compared with men (p < 0.005) and women not using OC (p < 0.05). So, in normal individuals the APC-sensitivity differs according to sex and estrogen intake. This should be taken into account when interpreting APC-ratios.
Henkens et al. (Sun,) studied this question.