A Log Built Around Time in Therapeutic Range, Not Single Readings
If you take warfarin, an INR tracker for warfarin is one of the few tools that turns scattered finger sticks into something you can actually act on.
If you have ever left an anticoagulation visit knowing only your latest number, with no sense of whether you are stable or quietly drifting out of range, you are not alone. Most clinics adjust the dose and move on. They rarely show you time in therapeutic range, the one number that actually predicts how warfarin is working for you.
If you are on warfarin for atrial fibrillation, your doctor has probably set your target INR somewhere around 2.0 to 3.0. What you may not have been told is that the most important warfarin metric is not any individual reading.
It is time in therapeutic range, or TTR. TTR is the percentage of days you spend inside your target range, and it predicts both stroke risk and bleeding risk better than any single INR value. The ranges discussed here are general guidelines. Your doctor sets the target that fits your history.
Most clinics do not show TTR to patients. They just adjust the dose. This template lets you calculate your own TTR between visits so you can see whether your anticoagulation is actually stable or whether you are bouncing around and did not know it.
Key Takeaways
- Time in therapeutic range, not a single INR, is the number that predicts warfarin effectiveness and safety.
- A TTR above 70 percent is considered well controlled. Below 60 percent is a signal for reassessment.
- Logging diet changes, new medications, and illness alongside INR values makes sudden swings explainable.
- Missed doses, missed meals, and antibiotic courses are the three most common reversible causes of INR instability.
- Bringing a six month INR log to every visit gives your anticoagulation clinic a full picture, not just the last reading.
What TTR Means and Why It Matters More Than Any Single INR
Warfarin is an effective anticoagulant, but its window is narrow. Too low and blood clots too easily, which is the original stroke risk you are trying to prevent. Too high and bleeding risk climbs sharply. For most people on warfarin for AFib the target window sits around 2.0 to 3.0, and the percentage of time spent inside that window is what predicts outcomes.
Research published in journals like Circulation and the Journal of Thrombosis and Haemostasis has consistently shown that a TTR above 70 percent is associated with significantly lower rates of both stroke and major bleeding compared with a TTR below 60 percent. That is a clinically meaningful difference, and it is the reason your clinic cares more about stability than any single reading.
The simple version of TTR is the percent of your INR readings that are inside range. A more accurate method called the Rosendaal method interpolates between readings, but the simple method is close enough for patient self tracking.
What to Log at Each Reading
Date and INR Value
Every reading, whether at a clinic, a lab, or a home meter. Note the source so you can compare values that came from different devices.
Target Range and In Range
Most AFib patients target 2.0 to 3.0. A few have a different range. Circle yes or no for whether this reading is in range. That yes or no column is what you will use to calculate TTR.
Current Warfarin Dose
Total weekly dose in milligrams. Write it as “5 mg x 5 days, 7.5 mg x 2 days” or whatever the actual pattern is. Weekly dose changes show up here when your clinic adjusts.
What Changed Since the Last Reading
This is the column that explains unexpected swings. New medication. Course of antibiotics. GI illness that cut food intake for a few days. Big diet change. Increased alcohol. Missed doses. If nothing changed, write nothing. If something changed, write it in one line. When an INR jumps out of range, this column is often where the explanation is hiding.
The INR Tracker for Warfarin: Log Format
| Date | INR | Target | In Range? | Weekly Dose | What Changed | Notes |
|---|---|---|---|---|---|---|
| __/__ | ___ | 2-3 | Y / N | ___ mg | _____________ | _____________ |
| __/__ | ___ | 2-3 | Y / N | ___ mg | _____________ | _____________ |
| __/__ | ___ | 2-3 | Y / N | ___ mg | _____________ | _____________ |
| __/__ | ___ | 2-3 | Y / N | ___ mg | _____________ | _____________ |
| __/__ | ___ | 2-3 | Y / N | ___ mg | _____________ | _____________ |
| __/__ | ___ | 2-3 | Y / N | ___ mg | _____________ | _____________ |
Your TTR is the number of in range readings divided by the total number of readings, as a percentage. Ten readings with seven in range is 70 percent. Simple calculation, clinically important number.
What to Do When a Reading Is Out of Range
An occasional out of range INR is normal on warfarin. A pattern of them is not. When the last three consecutive readings have all been out of range, or your TTR has stayed below 60 percent for a couple of months, that is a conversation to bring to your anticoagulation clinic. The options they consider might include a dose adjustment, a tighter follow up schedule, or a discussion about switching to a direct oral anticoagulant if the instability cannot be resolved.
Do not adjust your own dose without instructions. Warfarin has a long half life and dose changes take several days to fully take effect, so a panic adjustment based on one reading can swing the next reading the other way.
For a digital version that auto-calculates TTR and graphs your readings over time, the Clarity AFib tracker app handles the math and lets you share a summary with your clinic. For appointment prep alongside this log, see the AFib visit prep template, and for tracking the events behind your readings the AFib episode log template pairs well with this one.
What 30, 60, and 90 Days of Tracking Reveals
After a month you will have a baseline TTR. By month two you can see whether it is holding, climbing, or dropping. By the three month mark, the “what changed” column usually reveals the specific triggers in your own life that push your INR around. That is the information that lets you prevent the next out of range reading instead of reacting to it.
Your next INR draw is day one. Log it when you get the number.
The ranges in this post are general guidelines. Never change your warfarin dose without instruction from your anticoagulation clinic or prescriber.
Sources
- Circulation and the Journal of Thrombosis and Haemostasis: peer-reviewed research on time in therapeutic range and warfarin outcomes.
- CDC, Atrial Fibrillation: background on AFib and stroke prevention.
Frequently Asked Questions
What is a good INR range for AFib?
For most AFib patients on warfarin, the target INR range is 2.0 to 3.0. Your cardiologist may adjust this based on stroke and bleeding risk factors like your CHA2DS2-VASc score.
What is time in therapeutic range?
TTR measures the percentage of time your INR stays within your target range. A TTR above 65 to 70% is considered good control. Below 60% suggests the anticoagulation is unstable.
Medical disclaimer: This post is for informational purposes only and does not constitute medical advice. The content here is not a substitute for professional medical care, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health or a medical condition. If you are experiencing a medical emergency, call 911 or contact your local emergency services immediately.