Heparin Infusion Nomogram (aPTT / Anti-Factor Xa)
A titration table for unfractionated heparin (UFH) infusion in ICU and emergency care, by aPTT or anti-factor Xa result. Decision-support tool for physicians and nurses.
How to use
Initial bolus: 80 units/kg (total body weight; maximum 10,000 units). Initial infusion rate: 18 units/kg/hour (total body weight; maximum 2,000 units/hour). Use only one measure — anti-factor Xa activity OR aPTT — never both; they are rarely concordant. The aPTT ranges below must be validated with your institution's laboratory (reagent/instrumentation), as they vary between institutions.
Titration table
| aPTT (seconds) | Anti-Xa (IU/mL) | Action | Recheck |
|---|---|---|---|
| < 40 s | 0.00–0.09 IU/mL | Additional bolus of 25 units/kg. Increase infusion by 3 units/kg/hour. | 6 h |
| 40–49 s | 0.10–0.19 IU/mL | Increase infusion by 2 units/kg/hour. | 6 h |
| 50–69 s | 0.20–0.29 IU/mL | Increase infusion by 1 unit/kg/hour. | 6 h |
| 70–110 s (therapeutic range) | 0.30–0.70 IU/mL | No change (within therapeutic range). Once therapeutic for 2 consecutive assays, may switch to once-daily assays. | 6 h |
| 111–120 s | 0.71–0.79 IU/mL | Decrease infusion by 1 unit/kg/hour. | 6 h |
| 121–130 s | 0.80–0.89 IU/mL | Stop infusion for 1 hour, then decrease by 2 units/kg/hour. | 6 h after restarting the infusion |
| 131–140 s | 0.90–0.99 IU/mL | Stop infusion for 1 hour, then decrease by 3 units/kg/hour. | 6 h after restarting the infusion |
| 141–150 s | 1.00–1.09 IU/mL | Stop infusion for 2 hours, then decrease by 4 units/kg/hour. | 6 h after restarting the infusion |
| > 150 s | ≥ 1.10 IU/mL | Stop infusion for 2 hours, then decrease by 5 units/kg/hour and notify clinician. | 6 h after restarting the infusion |
Source: UpToDate® — "Nomogram for adjusting unfractionated heparin in adults using anti-factor Xa activity or the aPTT" (Graphic 122945, version 5.0). Courtesy of Allison E Burnett, PharmD, PhC, CACP. © UpToDate, Inc. This is one example nomogram; dosing intensity and clinical management should follow your institutional protocol for the indication (VTE, ACS, stroke, etc.).
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Frequently asked questions
- What is a heparin aPTT / anti-Xa nomogram?
- It's a reference table used to adjust the continuous infusion rate of unfractionated heparin based on the patient's aPTT or anti-factor Xa activity result, keeping anticoagulation within the therapeutic range.
- Should I use aPTT or anti-Xa to adjust heparin?
- Use only one measure at a time — aPTT OR anti-factor Xa — never both together, since they are rarely concordant. The choice usually follows institutional protocol.
- Do these aPTT ranges apply to any laboratory?
- No. They must be validated with your own institution's laboratory, since they vary by reagent and instrumentation.