Measurement of activated factor XII in health and disease.

We investigated a new ELISA for measuring activated factor XII (FXIIa) in plasma. The intra-assay coefficient of variation was 3.5% and 5.1% for plasma containing 2.5 and 8.2 ng/ml FXIIa. The inter-assay coefficient of variation was 6.2% and 6.6%. FXIIa correlated with age in women older than 55 years (r = 0.55, P = 0.0003). Mean levels in the whole population of 160 healthy individuals included in this study were not different between men and women, but women younger than 55 years had lower levels than older women and men of the corresponding age. In a group of 25 healthy centenarians FXIIa was significantly higher (3.2 ng/ ml, 95% CI 2.3-3.6) than in controls (2.1 ng/ml, 95% CI 1.8-2.4). Increased levels were also found in pregnancy, with higher levels in the third trimester (4.7 ng/ml, 95% CI 3.9-5.5) than in the first trimester (2.9 ng/ml, 95% CI 2.2-3.9). FXIIa was unmeasurable in patients with FXII deficiency, but normal in patients with FXI deficiency and C1-inhibitor deficiency. FXIIa was significantly higher than in normal controls in patients with severe sepsis (3.9 ng/ml, 95% CI 2.8-5.4) and septic shock (5.4 ng/ml, 95% CI 3.7-7.7). After treatment with thrombolytic agents, a marked increase of FXIIa was found in patients with myocardial infarction. In conclusion, the immunoassay of FXIIa permits to study more directly the contact phase of blood coagulation in situations in which the involvement of this system may play a pathophysiological role.