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 coeffi cient of variation was 6.2% and 6.6%. FXIIa correlated with age in wom en older than 55 years (r=0.55, P=0.0003). Mean levels in the whole po pulation of 160 healthy individuals included in this study were not di fferent between men and women, but women younger than 55 years had low er levels than older women and men of the corresponding age. In a grou p 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). Increa sed levels were also found in pregnancy, with higher levels in the thi rd 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 FX II deficiency, but normal in patients with FXI deficiency and C1-inhib itor deficiency. FXIIa was significantly higher than in normal control s in patients with severe sepsis (3.9 ng/ml, 95% CI 2.8-5.4) and septi c 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 myocard ial infarction. In conclusion, the immunoassay of FXIIa permits to stu dy more directly the contact phase of blood coagulation in situations in which the involvement of this system may play a pathophysiological role.