Monitoring Heparin Therapy: Relationships between the Activated Partial Thromboplastin Time and Heparin Assays Based on Ex-Vivo Heparin Samples

Summary

Five different APTT reagents, two amidolytic anti-ITa assays, one amidoiytic anti-Xa assay, and one coagulometric anti-Xa/ anti-IIa assay were used to assess the effect of heparin in patients treated for venous thromboembolic disease. Good correlations were observed between lug-transformed APYE> determined with the various reagents (correlation coefficients: 0.92-0.96).

Nevertheless there were important differences in the slopes of the lines of relationship between the APTT reagents.

Good correlations were observed between the anti-Xa and anti-IIa assay results (correlation coefficients: 0.92-0.97). However, the amidolytic anti-Xa activity was significantly higher (p <0.001) than the two amidolytic anti-IIa activities.

Less good correlations were observed between the log-transformed APTTs and the anti-Xa or anti-IIa activities (correlation coefficients: 0.64-0.78). The correlations were improved by transforming the APTT into APTT-ratio, i.e. the ratio of the patient’s APTT to the same patient’s APTT after removal of heparin from the plasma sample by means of ECTEOLA-cellulose treatment. The correlation coefficients of log (AFTT-ratio) with anti-Xa or anti-IIa ranged from 0.76 to 0.87.

For both APTT and amidolytic heparin assay, the response to in vitro heparin was different from the response to ex vivo heparin.

Therefore, equivalent therapeutic ranges should be assessed by using ex vivo samples rather than in vitro heparin. Because of the response differences between the APTT reagents, it is not adequate to define a therapeutic range for heparin therapy without specification of the reagent.

Keywords

Heparin monitoring - Activated partial thromboplastin time - Amidolytic heparin assay - Factor Xa-inhibition - Faxtor IIa-inhibition

• References

• 1 Banez EI, Triplett DA, Koepke J. Laboratory monitoring of heparin therapy - The effect of different salts of heparin on the activated partial thromboplastin time. Am J Clin Pathol 1980; 74: 569-574
• 2 Bain B, Forster T, Sleigh B. Heparin and the activated partial thromboplastin time - A difference between in-vitro and in-vivo effects and implications for the therapeutic range. Am J Clin Pathol 1980; 74: 668-673
• 3 Scialla SJ. Heparin monitoring by activated partial thromboplastin time. Comparison of ex vivo measurement and in vitro standardization. Am J Clin Pathol 1985; 84: 351-354
• 4 Basu D, Gallus A, Hirsh J, Cade J. A prospective study of the value of monitoring heparin treatment with the activated partial thromboplastin time. N Engl J Med 1972; 287: 324-327
• 5 Fennerty A, Campbell IA, Routledge PA. Anticoagulants in venous thromboembolism. Br Med J 1988; 297: 1285-1288
• 6 Juhan-Vague I, Riera H, Aillaud MF, Verdet D, Sambuc R. Measurement of blood heparin levels - Variation in results with assay method. Thromb Haemostas 1982; 47: 295
• 7 Holm HA, Abildgaard U, Larsen ML, Kalvenes S. Monitoring of heparin therapy: should heparin assays also reflect the patient’s antithrombin concentration?. Thromb Res 1987; 46: 669-675
• 8 Van den Besselaar A MH P, Meeuwisse-Braun J, Jansen-Grüter R, Bertina RM. Monitoring heparin therapy by the activated partial thromboplastin time. The effect of pre-analytical conditions. Thromb Haemostas 1987; 57: 226-231
• 9 Mitchell GA, Gargiulo RJ, Huseby RM, Lawson DE, Pochron SP, Sehuanes JA. Assay for plasma heparin using a synthetic peptide substrate for thrombin: Introduction of the fluorophore aminoisoph-thalic acid, dimethyl ester. Thromb Res 1978; 47-52
• 10 Bishop RC, Hudson PM, Mitchell GA, Pochron SP. Use of fluorogenic substrates for the assay of antithrombin III and heparin. Ann NY Acad Sci 1981; 370: 720-730
• 11 Bartl K, Dorsch E, Lill H, Ziegenhorn J. Determination of the biological activity of heparin by use of a chromogenic substrate. Thromb Haemostas 1979; 42: 1446-1451
• 12 Teien AN, Lie M. Evaluation of an amidolytic heparin assay method: Increased sensitivity by adding purified antithrombin III. Thromb Res 1977; 10: 399-410
• 13 Holmer E, Söderberg K, Friberger P, Sörskog L. A new simple chromogenic substrate assay for heparin and heparin-like anti-FXa activity in plasma. Thromb Haemostas 1985; 54: 29 (Abstr P168)
• 14 Yin ET, Wessler S, Butler JV, Cole S. Plasma heparin: a unique practical, submicrogram-sensitive assay. J Lab Clin Med 1973; 81: 298-310
• 15 Schuler J, Von Felten A. Eine einfache Methode zur Kontrolle der Antikoagulation mit Vitamin-K-Antagonisten unter Heparintherapie: Quick-Bestimmung nach Absorption des Heparins mittels ECTEOLA-Cellulose. Schweiz Med Wschr 1982; 112: 1798-1800
• 16 Ten Cate H, Lamping RJ, Henny ChP, Prins A, Ten Cate JW. Automated amidolytic method for determining heparin, a heparinoid, and a low-Mr heparin fragment, based on their anti-Xa activity. Clin Chem 1984; 30: 860-864
• 17 Morin RJ, Richards D. Effect of freezing heparinized plasma on the activated partial thromboplastin time. Am J Clin Pathol 1974; 61: 823-827
• 18 Levine SP, Sorenson RR, Harris MA, Knieriem LK. The effect of platelet factor 4 (PF4) on assays of plasma heparin. Br J Haematol 1984; 57: 585-596
• 19 Michalski R, Lane DA, Pepper DS, Kakkar VV. Neutralization of heparin in plasma by platelet factor 4 and protamine sulphate. Br J Haematol 1978; 38: 561-571
• 20 Poller L, Thomson JM, Yee KF. Heparin and partial thromboplastin time: an international survey. Br J Haematol 1980; 44: 161-165
• 21 Holm HA, Kalvenes S, Abildgaard U. Changes in plasma antithrombin (heparin cofactor activity) during intravenous heparin therapy: observations in 198 patients with deep venous thrombosis. Scand J Haematol 1985; 35: 564-569
• 22 de Swart CA M, Nijmeijer B, Roelofs JM M, Sixma JJ. Kinetics of intravenously administered heparin in normal humans. Blood 1982; 60: 1251-1258
• 23 Gallus AS, Hirsh J, Gent M. Relevance of preoperative and postoperative blood tests in postoperative leg vein thrombosis. Lancet 1973; ii: 805-809
• 24 Hauser VM, Rozek SL. Effect of warfarin on the activated partial thromboplastin time. Drug Inteil Clin Pharm 1986; 20: 964-967
• 25 Koepke JA. Partial Thromboplastin time test - Proposed performance guidelines. Thromb Haemostas 1986; 55: 143-144