Summary
The protein C inhibitor (PCI) concentration and other parameters of the protein C pathway were studied in 19 patients with symptomatic acute deep vein thrombosis before and during the first 5 days of heparin treatment. The mean levels of PCI antigen and activity decreased rapidly and significantly during the first day of heparin therapy from 83 and 81% to 60 and 59% of the pooled normal human plasma (p <0.01), respectively, and to 56 and 54% after 5 days of treatment (p <0.01). In contrast, antithrom-bin III decreased progressively 25% during 5 days of heparin treatment. Protein C antigen and activity and total protein S remained unchanged during heparin treatment. Free protein S was decreased before heparin treatment (83%, p <0.05) and increased to normal values after 5 days of treatment. C4b-binding protein was significantly increased before and during heparin treatment (p <0.01). Activated protein C (APC) complexed to its two major plasma inhibitors, PCI and α1-antitrypsin (α1AT) were measured by specific ELISA’s. Before treatment, 18 of the 19 patients studied had increased levels of APC: α1AT complexes with a mean value of 27 ± 22 ng/ml (range, 6−86 ng/ml) compared to normal values (8 ± 2 ng/ml) and 12 of the patients also had detectable APC:PCI complex levels with a mean value of 11 ±17 ng/ml (range, 5−68 ng/ml). Both APC:inhibitor complexes decreased significantly during heparin treatment.
