Heparin Nomogram (Weight-based)

Check aPTT or Anti-Xa levels 6 hours after any change in dose and 6 hours after the initial infusion start.

Patients who fail to reach therapeutic aPTT despite very high heparin doses (>35,000 units/day) may have "Heparin Resistance," often due to antithrombin III deficiency or high levels of factor VIII. Switching to Anti-Xa monitoring is more reliable in these cases.

Before the Raschke nomogram, heparin was often dosed using empirical "fixed-dose" schemes, which resulted in significant under-anticoagulation in large patients and bleed risk in small patients.