An International Collaborative Study on the Performance of Protein C Antigen Assays

Summary

An international collaborative study was undertaken to evaluate the performance and specificity of protein C antigen (PC) assays. Thirteen lyophilized plasma samples were distributed among 17 laboratories and analysed with 24 methods. No statistically significant results were obtained with the different methods in plasmas containing only the protein C zymogen. ELISA’s, RIA’s and IRMA’s were found to be more sensitive than the electro-immunoassay. In plasmas of patients on oral anticoagulant treatment ELISA methods tend to give lower PC antigen levels than the electro-immunoassay. Complexes between activated protein C (APC) and the protein C inhibitor (PCI), when present in plasma together with PC zymogen, are detected with 100% efficiency in the electro-immunoassay, with 50% efficiency in the ELISA, and with <10% efficiency in the RIA or in assays using monoclonal antibodies against PC.

Mean coefficient of variation was calculated to be 22%, and could be reduced - especially in case of the ELISA by normalisation. Within laboratory variation was calculated to be 11.7% and between laboratory variation 17.8%.

Keywords

Protein C antigen assay

• References

• 1 Esmon CT, Esmon NL. Protein C activation. Semin Thromb Haemost 1984; 10: 122-130
• 2 Walker FJ, Sexton PW, Esmon CT. The inhibition of blood coagulation by activated protein C through the selective inactivation of activated factor V. Biochimica et Biophysica Acta 1979; 571: 333-342
• 3 Fulcher CA, Gardiner JE, Griffin JH, Zimmerman TA. Proteolytic inactivation of human factor VIII procoagulant protein by activated protein C and its analogy with factor V. Blood 1984; 63: 486-489
• 4 Comp PC, Esmon CT. Generation of fibrinolytic activity by infusion of activated protein C in dogs. J Clin Invest 1981; 68: 1221-1228
• 5 Colluci M, Stassen JM, Collen DC. Influence of protein C activation on blood coagulation and fibrinolysis in squirrel monkeys. J Clin Invest 1984; 74: 200-204
• 6 De Fouw NJ, Haverkate F, Bertina RM, Koopman J, van Wijngaarden A, van Hinsbergh V WM. The cofactor role of protein S in the acceleration of whole blood clot lysis by activated protein C in vitro. Blood 1986; 67: 1189-1192
• 7 Walker FJ. Regulation of activated protein C by protein S. The role of phospholipid in factor Va inactivation. J Biol Chem 1981; 256: 11128-11131
• 8 Griffin JH, Evatt B, Zimmerman TS, Kleiss AJ, Wideman C. Deficiency of protein C in congenital thrombotic disease. J Clin Invest 1981; 68: 1370-1373
• 9 Broekmans AW, Veltkamp JJ, Bertina RM. Congenital protein C deficiency and venous thromboembolism. N Engl J Med 1983; 309: 340-344
• 10 Horellou MH, Conard J, Bertina RM, Samama M. Congenital protein C deficiency and thrombotic disease in nine French families. British Medical Journal 1984; 289: 1285-1287
• 11 Broekmans AW. Hereditary protein C deficiency. Haemostasis 1985; 15: 233-240
• 12 Broekmans AW, Van der Linden IK, Jansen-Koeter Y, Bertina RM. Prevalence of protein C (PC) and protein S (PS) deficiency in patients with thrombotic disease. Thromb Res 1986; Suppl VI 135 (Abstract)
• 13 Suzuki K, Nishioka J, Hashimoto S. Protein C inhibitor. Purification from human plasma and characterization. J Biol Chem 1983; 258: 163-168
• 14 Viganò S, Mannucci PM, Solinas S, Bottaso B, Mariani G. Decrease in protein C antigen and formation of an abnormal protein soon after starting oral anticoagulant therapy. Br J Haematol 1984; 57: 213-220
• 15 Bertina RM, Broekmans AW, van der Linden IK, Mertens K. Protein C deficiency in a Dutch family with thrombotic disease. Thromb Haemostas 1982; 48: 1-5
• 16 Boyer C, Rothschild C, Wolf M, Amiral J, Meyer D, Larrieu MJ. A new method for the estimation of protein C by ELISA. Thromb Res 1984; 36: 579-589
• 17 Epstein DJ, Bergum PW, Bajaj SP, Rapaport SI. Radioimmunoassays for protein C and factor X. Plasma antigen levels in abnormal heamostatic states. Am J Clin Pathology 1984; 82: 573-581
• 18 Suzuki K, Moriguchi A, Nagayoshi A, Mutoh S, Katsuki S, Hashimoto S. Enzyme immunoassay of human protein C by using monoclonal antibodies. Thromb Res 1985; 38: 611-621
• 19 Ikeda K, Stenflo J. A radioimmunoassay for protein C. Thromb Res 1985; 39: 297-306
• 20 Mikami S, Tuddenham E GD. Studies on immunological assay of vitamin K dependent factors. II. Comparison of four immunoassay methods with functional activity of protein C in human plasma. Br J Haematol 1986; 62: 183-192
• 21 Bertina RM, Broekmans AW, Krommenhoek-van EsC, van Wijngaarden A. The use of a functional and immunologic assay for plasma protein C in the study of the heterogeneity of congenital protein C deficiency. Thromb Haemostas 1984; 51: 1-5
• 22 Tripodi A, Valsechtie C, Botasso B, Sharon C, Mannucci PM. Comparison of a functional assay for protein C with two immunoassays. Thromb Res 1985; 40: 243-248