Warfarin scheme – reference ranges

Arrow In this section

These reference ranges are to help with interpreting results for patients on a Warfarin scheme.

Day APTT (9-10am) target Heparin dose IF INR Warfarin dose given at 5pm
1 Start 2-3 ratio As per APTT < 1.4 10 mg
2 As per APTT

< 1.8

10 mg

1.8 1 mg
> 1.8 0.5 mg
3 2-3 ratio As per APTT <2.0 10 mg
2.0-2.3 5 mg
2.4-2.7 4 mg
2.8-3.1 3 mg
3.2-3.4 2 mg
3.5-4.0 1 mg
>4.0 NIL
4 Stop heparin Predicted maintenance
>8 mg
<1.4 8 mg
1.4 7.5 mg
1.5 7 mg
1.6-1.7 6.5 mg
1.8 6 mg
1.9 5.5 mg
2.0-2.1 5 mg
2.2-2.3 4.5 mg
2.4-2.6 4 mg
2.7-3.0 3.5 mg
3.1-3.5 3
3.6-4.0
Nil then 2 mg
4.1-4.5
>4.5 Nil for two days and then 1mg

(Last reviewed November 2019)