Heparin Dosing Calculator

The Heparin Dosing Calculator provides weight-based unfractionated heparin (UFH) dosing for anticoagulation therapy. Unfractionated heparin remains a cornerstone of acute anticoagulation management in a wide range of clinical conditions, including venous thromboembolism (DVT and PE), acute coronary syndromes, atrial fibrillation, and cardiopulmonary bypass. Its rapid onset, short half-life, and reversibility with protamine make it uniquely suited for situations requiring precise, adjustable anticoagulation.

Weight-based heparin dosing protocols, pioneered by Raschke et al. in 1993, revolutionized heparin therapy by demonstrating superior achievement of therapeutic anticoagulation compared to fixed-dose nomograms. The landmark study showed that weight-based dosing (80 units/kg bolus followed by 18 units/kg/hour infusion for DVT/PE) achieved therapeutic aPTT within 24 hours in 97% of patients, compared to only 77% with standard dosing.

The dosing regimen varies by clinical indication. For DVT/PE treatment, the standard protocol uses an 80 units/kg bolus followed by 18 units/kg/hour continuous infusion, targeting an aPTT of 1.5-2.5 times control (typically 60-80 seconds). For acute coronary syndromes (ACS/NSTEMI), lower doses are recommended: 60 units/kg bolus (maximum 4000 units) and 12 units/kg/hour infusion (maximum 1000 units/hour), targeting an aPTT of 50-70 seconds to balance anticoagulation benefit against bleeding risk.

The aPTT (activated partial thromboplastin time) is the standard laboratory test for monitoring UFH therapy. However, aPTT reagent sensitivity varies between institutions, and each hospital should establish its own therapeutic range calibrated to anti-Xa levels of 0.3-0.7 IU/mL. Many institutions are transitioning to direct anti-Xa monitoring for heparin, which offers better correlation with clinical outcomes and less inter-laboratory variability.

Key considerations for heparin dosing include: obesity (many protocols cap bolus and infusion doses), renal function (minimal impact on UFH clearance unlike LMWH), hepatic function (may prolong response), concurrent antiplatelet therapy (increased bleeding risk), and heparin resistance (requiring higher doses, often seen with AT-III deficiency, acute inflammation, or large clot burden).

Heparin-induced thrombocytopenia (HIT) is the most feared complication, occurring in 1-5% of patients receiving UFH. Platelet counts should be monitored at baseline and every 2-3 days during therapy. A 50% drop in platelets or an absolute count below 150,000/microL should trigger HIT evaluation with a 4Ts score and immunoassay testing. If HIT is suspected, heparin must be discontinued immediately and a non-heparin anticoagulant substituted.

This calculator implements standard weight-based heparin protocols for common indications, including bolus calculation, initial infusion rate, and conversion to mL/hour based on standard 25,000 units/500 mL concentration. All doses should be verified against institutional protocols and adjusted based on laboratory monitoring.

Monitoring typically involves checking aPTT 6 hours after initiation or dose change, with subsequent adjustments according to institutional nomograms until the therapeutic range is consistently achieved.