Coagulation Study
PT / INR Calculator
International Normalized Ratio
sec
sec
index
Typically 0.9 – 1.4 · check reagent package insert
Calculated INR
—
Below normal< 0.9
Normal0.9 – 1.1
Mildly elevated1.1 – 2.0
Therapeutic (most)2.0 – 3.0
Therapeutic (high-risk)3.0 – 3.5
Significantly elevated> 3.5
INR = (Patient PT ÷ Control PT) ISI
Normal range 0.9 – 1.1
Warfarin (most) 2.0 – 3.0
Warfarin (high-risk)2.5 – 3.5
ISI typical range 0.9 – 1.4
