Activated protein C-protein C inhibitor complex: a new biological marker for aortic aneurysms

The concentration of the complex between activated protein C (APC) and protein C inhibitor (PCI) is a measure of thrombin generation. We studied whether it can provide information useful for the diagnosis and treatment of arterial vascular disease.

Blood was obtained from 429 vascular patients admitted consecutively during September 2004 to March 2005. The APC-PCI complex was measured by using a sandwich immunofluorometric method. The patients were divided into cohorts according to the planned treatment and compared with a control group of healthy individuals.

The APC-PCI complex concentration varied from 0.08 to 2.50 microg/L. In the cohort of patients with aortic aneurysms (n = 78), the median APC-PCI value was 0.45 (10th to 90th percentile, 0.24-1.47), and values were clearly increased compared with all other cohorts (P < .0001). Patients with carotid disease (n = 73) yielded a median of 0.22 (10th to 90th percentile, 0.15-0.48). The median for claudicants (n = 74) was 0.26 microg/L (10th to 90th percentile, 0.15-0.75), which was higher than in those (n = 97) with critical ischemia (0.20; 10th to 90th percentile, 0.13-0.36; P < .0023). The cohort with other forms of atherosclerotic disease (n = 40) had a median of 0.23 (10th to 90th percentile, 0.14-0.42), whereas the value for a cohort of 21 patients with venous disease was 0.19 (10th to 90th percentile, 0.10-0.34). The median was 0.15 (10th to 90th percentile, 0.10-0.23) for the control group (n = 121).

Patients with atherosclerosis had an increased APC-PCI concentration that corresponded to increased generation of thrombin. Patients with aortic aneurysm had a threefold higher median concentration than the control group. We suggest that this remarkable increase is caused by the local activation of coagulation, and we surmise that APC-PCI measurements can be used as a screening tool to identify patients with aortic aneurysms.