Silvana Viganò

DEFICIENCIES OF PROTEIN C, AN INHIBITOR OF BLOOD COAGULATION

Protein C is a vitamin-K-dependent plasma glycoprotein that when activated inhibits coagulation by selectively inactivating the active forms of factor V and factor VIII. A specific antiserum to protein C has been raised, and plasma protein C levels have been measured by means of an electroimmunoassay in several physiological and pathological conditions. In 60 healthy adults there were no differences in protein C related to age or sex; protein C levels ranged from 72 to 139% of values in a normal plasma pool. Low levels were found in 12 healthy full-term newborn infants; the levels in 20 women in the last trimester of normal pregnancy were no different from those in healthy non-pregnant women. In 58 patients with chronic liver diseases protein C levels were lower than those in healthy subjects, in degrees roughly proportional to the severity of the disease. Protein C levels were very low in 21 patients with the disseminated intravascular coagulation syndrome, particularly in those who had evidence of consumption coagulopathy. Very low levels were also found, however, in 20 patients with adult respiratory distress syndrome without consumption coagulopathy. Acquired defects of protein C developed after surgery in the patients operated on for malignancies, after major abdominal operations for benign conditions, and also after relatively minor procedures such as appendicectomy and hernia repair. These findings indicate that protein C deficiencies occur in several conditions associated with increased tendency to thrombosis.

Decrease in protein C antigen and formation of an abnormal protein soon after starting oral anticoagulant therapy.

Summary. Changes in protein C antigen (PC: Ag) have been compared with those in factor II, VII, IX and X antigens (II:Ag; VII:Ag; IX:Ag and X: Ag) in 10 patients starting on oral anticoagulant therapy with warfarin, monitored with thrombotest. Between days 0 and 3 of therapy, PC: Ag decreased at the same rate as VII: Ag, whilst IX: Ag, X: Ag and II: Ag decreased at progressively slower rates. On days 15 and 21, clotting proteins and PC: Ag did not differ significantly. Before and after warfarin, PC: Ag had the same mobility on crossed immunoelectrophoresis in Ca2+‐free agarose gel; with Ca2+, a protein with faster anodal mobility appeared on day 1 and became maximal 5 d after warfarin was started. These findings indicate that the rate of PC decrease is closer to that of factor VII than those of factors IX, X and II, and that an abnormal PC with poor Ca2+‐binding properties appears soon after treatment is started. The early decrease in the physiological inactivator (i.e. PC) might contribute to the poor antithrombotic efficacy of anticoagulant therapy during the first days.

Use of INR calibrator plasmas in the routine coagulation laboratory: A study of two thrombolastin reagents

INR values may be either calculated with the ISI values supplied by thromboplastin manufacturers or are directly extrapolated from certified INR calibrator plasmas. We tested the principle of local INR calibration using INR calibrator plasmas (PT-Multi Calibrator, Siemens), two thromboplastin reagents (Neoplastin Plus, rabbit brain, Stago, coagulometer-specific ISI 1.31, and Innovin, recombinant human tissue factor, Siemens) and the same coagulometer (STA-R, Stago) in 100 patients on warfarin. Using a ISI value of 0.77 with Tomenson correction for Innovin (correction factor=1.09), INR values of patients were similar with the two reagents, with a bias of 0.03 INR units and no significant regression of the difference over the average INR by method comparison analysis. With the INR calibrator plasmas, INR values with Neoplastin Plus were lower than Innovin values with an average bias of 0.39 INR units and a significant regression of the difference over the average INR (r=-0.91). Significant bias (0.16 INR units, p<0.00001) and regression (r=-0.77) was also observed by comparison of Neoplastin Plus INRs with Innovin calibrated INRs. Based on a therapeutic INR interval of 2.0 to 3.5, discordance in warfarin dosing was approximately 3 times higher with INR calibration (27% vs 11%). Because of non commutability with fresh plasma samples, local INR calibration with lyophilized calibrator plasmas may not be valid for some reagent-instrument combinations.