Multicenter Comparison of Five Functional and Two Immunological Assays for Protein C

Protein C in acute renal failure

In 16 patients with acute renal failure we studied protein C activity, both coagulant and amidolytic, as well as protein C antigen level. Protein C coagulant activity was markedly decreased in acute renal failure. Furthermore, changes in kidney function were paralleled by alterations in protein C coagulant activity. The amidolytic activity and antigen level of protein C were normal in most cases, and the changes observed in a few patients seem clearly related to changes in liver function. This defective protein C could contribute to the thrombotic tendency reported in patients with acute renal failure.

Abdominoplasty: thromboembolic risks for both sexes

During surgical procedures, coagulation complications may occur. Discriminating factors are multiple and may vary because of the anatomical regions involved and because of preexisting diseases. The aim of this study was to analyze changes in such hematological parameters of patients undergoing conventional abdominoplasty with standard surgical procedures under general anaesthesia. For the study, 40 patients (20 men and 20 women) 30 to 60 years with normal coagulation assessments, no previous or current history of hemorrhagic or thrombotic disease, and no primary family history of such problems were selected. All the patients underwent conventional abdominoplasty surgical procedures. Analysis of the results suggests that immediately after surgery, in the absence of any preexisting hypo- or hypercoagulability state, there was no circumstantial modification in coagulation factors considered predictive for thromboembolic risk. However, an interesting difference between male and female patients was noted. In the male group, there was an insignificant uniform downward trend of all values immediately after surgery. In conclusion, women are less hypercoagulative than men in the postoperative period, suggesting that women have limited protection from the development of thromboembolic complications immediately after surgical procedures.

Laboratory issues in diagnosing abnormalities of protein C, thrombomodulin, and endothelial cell protein C receptor

OBJECTIVE

To review the current understanding of the pathophysiology of protein C deficiency and its role in congenital thrombophilia. Recommendations for diagnostic testing for protein C function and concentration, derived from the medical literature and consensus opinions of recognized experts in the field, are included, specifying whom, how, and when to test. The role of related proteins, such as thrombomodulin and endothelial protein C receptor, is also reviewed. Data Sources.-Review of the published medical literature.

DATA EXTRACTION AND SYNTHESIS

A summary of the medical literature and proposed testing recommendations were prepared and presented at the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. After discussion at the conference, consensus recommendations presented in this manuscript were accepted after a two-thirds majority vote by the participants.

CONCLUSIONS

Protein C deficiency is an uncommon genetic abnormality that may be a contributing cause of thrombophilia, often in conjunction with other genetic or acquired risk factors. When assay of protein C plasma levels is included in the laboratory evaluation of thrombophilia, a functional amidolytic protein C assay should be used for initial testing. The diagnosis of protein C deficiency should be established only after other acquired causes of protein C deficiency are excluded. A low protein C level should be confirmed with a subsequent assay on a new specimen. Antigenic protein C assays may be of benefit in subclassification of the type of protein C deficiency. The role of thrombomodulin and endothelial cell protein C receptor in thrombosis has yet to be clearly established, and diagnostic testing is not recommended at this time.

Protein S and protein C anticoagulant activity in acute and chronic cardiac ischemic syndromes. Relationship to inflammation, complement activation and in vivo thrombin activity

Protein S (PS) and protein C (PC) anticoagulant activities and thrombin-antithrombin complex (TAT) were measured in 20 patients with AIS, 25 patients with chronic stable angina (CSA) and a control group (C). Although plasma levels of TAT were significantly elevated in patients with CSA (p < 0.01 vs C), they were much higher in patients with AIS (p < 0.001 vs CSA). PC anticoagulant activity was similar in patients and controls. At variance, PS anticoagulant activity was lower in patients with AIS than in those with CSA and controls (p < 0.05), reflecting differences in total PS and C4B-binding protein (C4B-BP) antigen possibly resulting from involvement in the mechanisms of inflammation, complement activation and acute-phase response. The ratios of anticoagulant PS and PC to procoagulant vitamin K-dependent factors IX and II were reduced in AIS patients (0.05 > p > 0.005 vs C). In addition, the ratios of anticoagulant PC and PS to factor IX were lower in patients with AIS than in those with CSA (p < 0.05). These results indicate that in patients with acute ischemic cardiac syndromes the markedly increased in vivo thrombin generation is associated with an unbalance between coagulant and anticoagulant vitamin K-dependent factors.

Protein C and protein S levels in uremic patients before and after dialysis

The inhibitory capacity of the natural protein C (PC)/protein S (PS) system was evaluated measuring both the functional activity and the antigen level of both these inhibitors in 30 uremic patients before and after a dialytic treatment and in 30 healthy normal volunteers. PC functional activity was determined by two methods, one clotting and one chromogenic. PS antigen level was measured both as free protein and as total content. Unlike previous authors, we found that PC functional activity and the antigen level were normal in patients before dialysis, with a significant increase after. PS functional activity and free and total antigen levels were all normal before dialysis, and all except free antigen showed a significant post-treatment rise.

Evaluation of a new protein-C concentrate and comparison of protein-C assays in a child with congenital protein-C deficiency

We investigated a new protein-C (PC) concentrate in a child with a type-II homozygous deficiency, concerning tolerance and safety. By means of various functional and antigen assays the in vivo recovery and the half-life were determined. In order to compare the results we reduced the measured values to the average half-life of 10.0 +/- 0.5 h and to an optimal recovery of 96.6%. Considerable discrepancies observed in the response of functional (clotting) and both the amidolytic and antigen assays are characteristic for type II and anticoagulant treatment. The substituted protein C is activated by the endogenous system. Thus, the efficacy of activation can be determined in deficiency states. The antigen activity of one unit PC concentrate was found to be 120% (or 1.2 U/ml plasma), close to the 100% activity defined for endogenous PC.

Specificity of protein C and protein S assays

Specific tests for the measurement of protein C antigen and activity and protein S antigen are used in the clinical laboratory for the routine diagnosis of hereditary protein C and protein S deficiency. The performance of these tests is reviewed and discussed. Special attention is paid to the application of these tests for the analysis of patients on oral anticoagulant therapy.

Role of protein C in childhood cerebrovascular occlusive accidents

A group of 23 children with cerebrovascular occlusion of unknown etiology were re-evaluated 6 months-2 years later. Plasma protein C levels were determined with the coagulation method and were low in 10 cases. The role of this deficiency and the necessity of this test in cerebrovascular occlusion is discussed.

Clinical evaluation of protein C: a comparative review of antigenic and functional assays

Thromboembolic disease is a major complication of protein C (PC) deficiency, which is among the increasing number of recognized causes of hereditary thrombotic disease. The laboratory evaluation of PC is of the utmost importance in the accurate diagnosis of this deficiency. In this review, we describe the various types of clinical antigenic and activity assays of PC. The attributes of each type of assay are discussed, as well as the value of each assay in diagnosing the various acquired and hereditary deficiencies of PC. This basic review is intended for laboratories planning to institute PC assays.

Protein C assays in uremia

Protein C was determined in 42 patients with terminal uremia and 20 healthy controls in three different ways 1) anticoagulant activity 2) amidolytic activity 3) antigen level. Protein C anticoagulant activity was markedly decreased in uremia, but was partly normalized during hemodialysis treatment, whereas the amidolytic activity and antigen level of protein C were normal and without changes during dialysis. The activities and antigen levels of factor II and X were normal before and after hemodialysis. In anticoagulated patients we found a good correlation between prothrombin levels and protein C levels determined with three different assays. We did not find any evidence for a defect carboxylation of protein C as the cause for the defective protein C in uremia. The BaCl2 precipitation in the Protein C anticoagulant assay was incomplete both in uremia and in controls but without differences between the two groups. In vitro addition of urea and creatinine did not decrease protein C activity. The cause of the defective protein C in uremia is still not known but it might contribute to thromboembolic complications.

Fast functional assay of protein C in whole plasma using a snake venom activator: evaluation in patients with congenital and acquired protein C deficiencies

Both anticoagulant and amidolytic activities of protein C (PC) were measured using a snake venom activator in 4 patients with hereditary PC deficiency, 37 with disseminated intravascular coagulation (DIC), and 30 under stabilized warfarin therapy. The results were compared with those obtained by an immunological assay (ELISA). PC levels measured by different functional and immunological assays were very close in patients with hereditary PC deficiency and DIC. In patients under stable oral anticoagulant therapy, there was no detectable difference between amidolytic activity and antigen levels of PC in each patient plasma, whereas a decrease in anticoagulant activity was much more pronounced. These results indicate that the present activity assays measure PC specifically, and that the snake venom activator is capable of activating both carboxylated and hypocarboxylated forms of PC, but only anticoagulant assay can evaluate the physiological PC function in vitamin K-deficient states.

Association of inherited dysfibrinogenaemia and protein C deficiency in two unrelated families

An inherited association of dysfibrinogenaemia and protein C deficiency was found in three members of the same family. The propositus was a 48-year-old man who suffered from severe and rapidly complicated atherosclerosis of the aorta and lower limbs arteries, which perhaps suggests that the association of these two molecular abnormalities may have enhanced the thrombotic process. The abnormal fibrinogen had a reduced ability to bind thrombin which may be thrombogenic. We found the same inherited association of dysfibrinogenaemia and protein C deficiency in a patient with venous thrombosis. The functional abnormality of the fibrinogen, which could have been responsible for thrombosis, was delayed proteolysis by plasmin. Not only fibrinogen, but also fibrin clots were resistant to plasmic degradation. These observations raise two questions: (1) Is the association of a protein C deficiency with a dysfibrinogenaemia fortuitous or the result of a common mechanism? (2) Is there a link between an increased thrombotic tendency and either both of the defects of haemostasis that we have found, or only one of them?

Inherited factors in thrombosis

Patients with inherited defects or abnormalities that impair the naturally-occurring anticoagulant and fibrinolytic systems are at risk of developing venous and, more rarely, arterial thromboembolism. The prevalence of inherited thrombophilia in the general population is higher than that of inherited bleeding disorders (ca. 1 in 7500 vs 1 in 20,000). Low levels or dysfunctional forms of antithrombin III, protein C and protein S and abnormal fibrinogens are the most frequent and well-established inherited causes for thrombosis. Less frequent and/or less established causes are low heparin cofactor II and plasminogen and high levels of plasminogen activator inhibitor and histidine-rich glycoprotein. The pathophysiology, genetic and clinical aspects and laboratory diagnosis of inherited thrombotic disorders are reviewed and an approach to prophylaxis and therapy is outlined.

Quantitative determination of human protein C. Evaluation of a "fast" functional assay in comparison to a "traditional" functional and an immunological assay

A fast functional assay for protein C was evaluated and compared with a traditional functional and an enzyme linked immunosorbent assay in parallel for the same plasma samples derived from 43 healthy subjects, 12 patients with severe hepatic dysfunction, and 23 patients under stable oral anticoagulation. By all three test systems significantly lower levels of protein C were obtained in both groups of patients compared with normal subjects (p less than 0.0001). No significant between - assay differences were found in normal subjects and in patients with hepatic dysfunction; by correlation analysis coefficients higher than 0.8 were calculated between the measurements of the three tests. In patients under stable oral anticoagulation, however, the immunologic test yielded higher values than the traditional (p less than 0.05) and, more pronounced, the fast functional assay (p less than 0.0001); no or only borderline significant correlations between the results were found. In these patients protein C levels measured with the traditional functional assay were in the same range as the activity levels of factors II, VII, IX, and X, whereas the fast functional test yielded significantly lower levels. The presented results indicate that very similar protein C levels were obtained with both functional and the immunologic assay except in patients under oral anticoagulation.