Abstract:To investigate the relationship between the clinical diagnosis of thromboembolic disease and heparin requirements for anticoagulation, we prospectively studied 31 patients suspected to have either deep vein thrombosis or pulmonary embolism. Six had the diagnosis of pulmonary embolism confirmed by a combination of ventilation and perfusion scans with pulmonary angiography, eight had venograms showing deep vein thrombosis, seven had diseases which mimicked pulmonary embolism, and ten had normal venograms. These four diagnostic groups were not significantly different with respect to heparin requirements during the first 24 hours of therapy (x̄ ± S.D. = 426 ± 105, 507 ± 105, 434 ± 79, and 457 ± 46 units/kg per 24 hours, respectively). Patients with pulmonary embolism and deep vein thrombosis did not differ significantly with respect to heparin requirements (UNITS/kg per 24 hours) on the second (386 ± 108 vs. 439 ± 127), third (415 ± 136 vs. 464 ± 130), and fourth (374 ± 104 vs. 418 ± 127) days of therapy. Our data suggest that the clinical diagnosis does not affect the dose of heparin necessary to anticoagulate patients with pulmonary embolism and deep vein