Why use it

Weight-based heparin dosing achieves therapeutic aPTT faster and more reliably than fixed-dose protocols, reducing recurrent VTE and bleeding complications.

About

Weight-based unfractionated heparin (UFH) dosing calculator for VTE treatment and ACS. Based on the Raschke nomogram. Calculates initial bolus dose, starting infusion rate, and aPTT-based adjustment guidance.

When to use

Treatment of DVT or PE
ACS (NSTEMI/UA) with planned catheterization
Bridge anticoagulation
Prophylaxis in high-risk surgical patients (adjusted dosing)

Formula

VTE treatment: Bolus: 80 U/kg IV (max 10,000 U) Initial rate: 18 U/kg/hr Rate in mL/hr (if 100 U/mL standard bag) = (U/kg/hr × weight) / 100 ACS (NSTEMI): Bolus: 60 U/kg IV (max 4,000 U) Initial rate: 12 U/kg/hr (max 1,000 U/hr)

Pearls & pitfalls

Use actual body weight (ABW) for dosing; cap at 10,000 U bolus for obese patients.
Standard bag: 25,000 U in 250 mL NS = 100 U/mL.
aPTT subtherapeutic (<60s): rebols 40 U/kg + increase rate by 2 U/kg/h.
aPTT supratherapeutic (>100s): hold 1h + decrease rate by 3 U/kg/h.
Monitor platelets every 2-3 days (HIT screening).
Hold 4-6h before procedures; restart without bolus.

Next steps

Check aPTT 6 hours after initiation. Adjust infusion per institutional nomogram. Target aPTT typically 60-100 seconds (corresponds to anti-Xa 0.3-0.7 U/mL). Recheck aPTT 6h after each change.

Evidence

Raschke RA et al. JAMA 1993. Weight-based heparin protocol vs. standard-dose: therapeutic aPTT achieved faster (mean 17h vs. 27h, p<0.001).

References

Raschke RA et al. The weight-based heparin dosing nomogram compared with a "standard care" nomogram. JAMA. 1993;270(19):2317-2321. — link
Kearon C et al. Antithrombotic Therapy for VTE Disease. CHEST. 2016;149(2):315-352. — link

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