This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
Weight-based heparin
Unfractionated heparin (UFH) is an injectable anticoagulant used in hospital, often by continuous intravenous infusion. Because its effect varies widely between patients, it is started with a weight-based regimen and then adjusted to laboratory results.
Common starting regimens
| Indication | Bolus | Starting infusion |
|---|---|---|
| Venous thromboembolism (DVT, PE) | 80 units/kg | 18 units/kg/h |
| Acute coronary syndrome | 60 units/kg, max 4,000 units | 12 units/kg/h, max 1,000 units/h |
The venous thromboembolism regimen comes from the weight-based nomogram published by Raschke and colleagues in 1993; the acute coronary syndrome regimen follows cardiology guidelines and is capped to limit bleeding when heparin is combined with antiplatelet drugs.
Example
A 176 lb (80 kg) patient treated for a pulmonary embolism:
- bolus: 80 × 80 = 6,400 units;
- infusion: 18 × 80 = 1,440 units/h;
- with a solution of 25,000 units in 250 mL (100 units/mL), the pump runs at 14.4 mL/h, and the bolus is 64 mL drawn from a separate vial or given from the bag according to local practice.
Monitoring and adjustment
The dose is adjusted to the aPTT (activated partial thromboplastin time), typically aiming for 1.5 to 2.5 times the control value, or to the anti-Xa level, typically 0.3 to 0.7 units/mL. The first check is usually about 6 hours after the start and after each change. Each hospital uses its own nomogram, because aPTT reagents differ.
Platelet counts are also monitored to detect heparin-induced thrombocytopenia (HIT), a rare but serious immune reaction.
Points of caution
- Dosing weight: many protocols use actual body weight, sometimes with a cap or an adjusted weight in obesity.
- High-risk bleeding situations, recent surgery, low platelets or kidney or liver disease change the plan.
- Heparin is a high-alert medication: double-check concentrations, pump programming and units.
- Protamine sulfate reverses heparin in case of overdose or bleeding.
This calculator illustrates the arithmetic of published regimens. Dosing decisions belong to the treating team, following the local protocol.