INR Variability (Fihn Variance Growth Rate)
How unstable warfarin control has been, as Fihn's variance growth rate (method A).
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- INRs, one per line
- 2.0 2 3.5 1 2.5 2
- Target INR
- 2.5
Result: Fihn variance growth rate 0.38 over 3 INRs (target 2.5).
The tool opens with these values already filled in. Replace them with your own.
What you enter
- INRs, one per line: INR then weeks since the previous INR
- Target INR
How this is calculated
Citation
Fihn SD et al. Risk factors for complications of chronic anticoagulation. Ann Intern Med. 1993;118:511-520. Formula (method A) as printed in Ibrahim S, Jespersen J, Poller L. J Thromb Haemost. 2013;11:1540-1546, Figure 1. Read the sources: Fihn 1993 ↗, Ibrahim 2013 (Figure 1) ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.