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Assay of protein C in human plasma: comparison of amidolytic, coagulation, and immunochemical assays
Insights
Functional protein C coagulant assays are recommended for patients on oral anticoagulant therapy. This method accurately reflects in vivo protein C function, unlike amidolytic or immunochemical assays in this specific group.
Area of Science:
- Biochemistry
- Hematology
- Clinical Chemistry
Background:
- Protein C is a crucial anticoagulant protein.
- Assessing protein C activity is important in various clinical conditions.
- Different assays exist to measure protein C, including functional (coagulant, amidolytic) and antigen levels.
Purpose of the Study:
- To compare functional protein C activity (coagulant and amidolytic) and antigen levels across different patient groups.
- To evaluate the correlation between various protein C assays.
- To determine the most suitable assay for protein C measurement in patients on oral anticoagulant therapy.
Main Methods:
- Studied protein C activity and antigen in normal subjects, patients with protein C deficiency, preeclampsia, coronary heart disease, disseminated intravascular coagulation, and those on oral anticoagulants.
- Compared results from coagulant, amidolytic, and immunochemical protein C assays.
Main Results:
- All activity assays (amidolytic and coagulant) correlated significantly with each other and with the immunochemical assay across most groups.
- In patients on oral anticoagulants, the coagulant assay yielded lower protein C values compared to amidolytic and immunochemical assays.
- Excellent correlations were observed between all assay types (r > 0.90, p < 0.001) when excluding patients on oral anticoagulants.
Conclusions:
- The functional protein C coagulant assay is recommended for patients on stable oral anticoagulant therapy.
- This assay uniquely assesses the in vivo protein C function in patients undergoing anticoagulant treatment.
- Standard assays may not accurately reflect functional protein C status in patients on oral anticoagulants.
Abstract:
We studied functional protein C activity, both anticoagulant and amidolytic, as well as protein C antigen in 30 normal subjects, several members of a family with congenital protein C deficiency, 18 patients with severe preeclampsia, 27 patients with coronary heart disease, including 15 patients with myocardial infarction and 12 with angina pectoris, 20 patients on stable oral anticoagulant therapy (thrombotest values: 3-12%) and three patients with disseminated intravascular coagulation. Protein C values measured by the coagulant assay were compared to those obtained with amidolytic and immunochemical assays. In all the groups studied, the activity assays (amidolytic and coagulant) correlated significantly with each other as well as with the immunochemical assay. In patients on oral anticoagulant therapy the coagulant assay gave lower protein C values than amidolytic and immunochemical assays. A good correlation was found between immunological and amidolytic protein C assays (r=0.90, p less than 0.001), immunological and coagulant protein C assays (r=0.93, p less than 0.001), and amidolytic and coagulant protein C assays (r=0.95, p less than 0.001) in all the samples studied without including the protein C values of patients on oral anticoagulant therapy. These results allow us to recommend the functional protein C coagulant assay in patients on stable oral anticoagulant therapy because only this assay evaluates the "in vivo" protein C function in these patients.