The Therapeutic Range for Heparin Therapy: Relationship between Six Activated Partial Thromboplastin Time Reagents and Two Heparin Assays

Summary

The activated partial thromboplastin time (APTT) is the most commonly used test for laboratory monitoring of unfractionated heparin therapy. Since there are differences between APTT reagents in respect of responsiveness to heparin the widely used therapeutic range of 1.5-2.5 (APTT ratios) may not be appropriate for all reagents.

The aim of this study was to assess the relationship between 6 different APTT reagents using a manual technique, 2 of these reagents used in combination with a coagulometer, a heparin assay by protamine titration and a chromogenic anti-Xa assay. Samples from 42 patients treated with unfractionated heparin for thromboembolic disease were studied, 12 of whom were receiving warfarin therapy with International Normalised Ratios (INR) of >1.3.

For normal subjects, APTT results were highly dependent on the method used and statistically significant differences were noted. The ratio of patient to mean normal APTT was calculated for each APTT method. When 30 samples from heparinised patients (with INRs of <1.3) were analysed manually, the APTT ranges equivalent to 0.2-0.4 u/ml heparin by protamine titration (by regression analysis) were 1.6-1.9 for Boehringer reagent (the least responsive) up to 2.2-2.9 for Instrumentation Laboratory reagent (the most responsive). The concentration of heparin associated on average with APTT ratios of 1.5-2.5 varied approximately twofold to threefold between reagents.

• References

• 1 Bounameaux H, Marbet GA, Lammle B, Eichlisberger R, Duckert F. Monitoring of heparin treatment: Comparison of thrombin time, activated partial thromboplastin time and plasma heparin concentration, and analysis of behaviour of anti-thrombin-III. Am J Clin Path 1980; 74: 68-73
• 2 Brandt JT, Triplett DA. Laboratory monitoring of heparin: Effect of reagents and instruments on the activated partial thromboplastin time. Am J Clin Path 1981; 76: 530-537
• 3 van den Besselaar AMHP, Meesuiwiesse-Braun J, Bertina RM. Monitoring heparin therapy: Relationships between the APTT and Heparin assays based on ex-vivo heparin samples. Thromb Haemost 1990; 63: 16-23
• 4 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 Path 1980; 74: 569-574
• 5 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
• 6 Hull RD, Raskob GE, Pineo GF, Green D, Trowbridge AA, Elliott CG, Lerner RG, Hall J, Sparling T, Bretnell HR, Norton J, Carter CJ, George R, Merli G, Ward J, Mayo W, Rosenbloom D, Brant R. Subcutaneous low molecular weight heparin compared with continuous intravenous heparin in the treatment of proximal-vein thrombosis. N Engl J Med 1992; 326: 975-982
• 7 Shojania AM, Tetreault J, Turnbull G. The variations between heparin sensitivity of different lots of activated partial thromboplastin reagents produced by the same manufacturer. Am J Clin Path 1988; 89: 19-23
• 8 Ray M, Carroll P, Smith I, Hawson G. An attempt to standardise activated partial thromboplastin time reagents used to monitor heparin therapy. Blood Coag Fibrinol 1992; 3: 743-748
• 9 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 Path 1980; 74: 668-673
• 10 Scialla SJ. Heparin monitoring by the activated partial thromboplastin time: Comparison of ex vivo measurement and in vitro standardisation. Am J Clin Path 1985; 84: 351-354
• 11 Kitchen S, Woods TAL, Jennings I, Preston FE. An improved method of external quality assessment of heparin dosage. Brit J Haem 1994; 86 (Suppl. 01) 34
• 12 Hirsh J. Heparin. N Engl J Med 1991; 324: 1565-1574
• 13 Abildgaard U, Norrheim L, Larsen AE, Nesvold A, Sanset PM, Odegaard OR. Monitoring therapy with low molecular weight heparin: A comparison of 3 chromogenic substrate assays and the Heptest clotting assay. Haemostas 1990; 20: 193-203
• 14 Refn I, Vestergaard L. The titration of heparin with protamine. Scand J Clin Lab Invest 1954; 6: 284-287
• 15 Brill-Edwards P, Ginsberg JS, Johnston M, Hirsh J. Establishing a therapeutic range for heparin. Ann Int Med 1993; 119: 104-109
• 16 Draper NR, Smith H. In: Applied Regression Analysis 2nd. Edition Chichester: Wiley & Sons; 1981: 97-99
• 17 Hoffman JJML, Meulendijk PN. Comparison of reagents for determining the activated partial thromboplastin time. Thromb Haemost 1978; 39: 640-645
• 18 Hathaway WE, Assmus SL, Montgomery RR, Dubansky AS. Activated partial thromboplastin time and minor coagulopathies. Am J Clin Path 1979; 71: 22-25
• 19 Howarth S. Activated partial thromboplastin time reagents: An evaluation. Br J Biomedical Science 1993; 50: 109-113
• 20 Barrowcliffe TW, Gray E. Studies of phospholipid reagents used in coagulation I: Some general properties and their sensitivity to factor VIII. Thromb Haemost 1981; 46: 629-633
• 21 Stevenson KJ, Easton AC, Curry A, Thompson JM, Poller L. The reliability of activated partial thromboplastin time methods and the relationship to lipid composition and ultrastructure. Thromb Haemost 1986; 55: 250-258
• 22 Barrowcliffe TW, Gray E. Studies of phospholipid reagents used in coagulation II: Factors influencing their sensitivity to heparin. Thromb Haemost 1981; 46: 634-637
• 23 Hull RD, Raskob GE, Hirsh J, Jay RM, Leclerc JR, Geerts WH, Rosenbloom D, Sackett DL, Anderson C, Harrison L, Gent M. Continuous intravenous heparin compared with intermittent subcutaneous heparin in the initial treatment of proximal vein thrombosis. N Engl J Med 1986; 315: 1109-1114
• 24 Hull RD, Raskob GE, Rosenbloom D, Panju AA, Brill-Edwards P, Ginsberg JS, Hirsh J, Martin GJ, Green D. Heparin for 5 days as compared with 10 days in the initial treatment of proximal venous thrombosis. N Engl J Med 1990; 332: 1260-1264
• 25 Turpie AGG, Robinson JG, Doyle DJ, Mulji AS, Mishkell GJ, Sealey BJ, Cairns JA, Skingley L, Hirsh J, Gent M. Comparison of high-dose with low-dose subcutaneous heparin to prevent left ventricular mural thrombosis in patients with acute transmural anterior myocardial infarction. N Engl J Med 1989; 320: 352-357
• 26 Levine M, Hirsh J, Gent M, Turpie AGG, Cruikshank M, Weitz J, Anderson D, Johnson M. A randomised trial comparing activated partial thromboplastin time with heparin assay in patients with acute venous thrombosis requiring large daily doses of heparin. Arch Intern Med 1994; 154: 49-56
• 27 Hull RD, Raskob GE, Rosenbloom D, Lemaire J, Pineo GF, Bayliss B, Ginsberg JS, Panju AA, Brill-Edwards P, Brant R. Optimal therapeutic level of heparin therapy in patients with venous thrombosis. Arch Intern Med 1992; 152: 1589-1595