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How I measure my INR when I travel

5 min read

Ivan Georgiev — patient and developer of INRythm

In short

  • I test my INR the morning before a trip and the morning after I return — two numbers that bracket the trip.
  • A week of unfamiliar food can move INR either way; after a week in Vienna mine fell from 2.92 to 1.72 without my noticing.
  • The tests give my doctor the information. I never change a dose on my own, and neither does the app.
  • Same lab every time, tablets in hand luggage, and log every dose and test with its date.

Also available in: BGEN

I've been on Sintrom since my heart surgery. Most of the year my INR is boring, which is exactly how I like it: the same three-day dose pattern my doctor set (3 mg, 4 mg, 4 mg, repeat), the same breakfast, a test once a month, the same number inside my target range.

Travel breaks all of that. Not the doses — I follow the same pattern wherever I am — but everything around the doses. And I learned, the uncomfortable way, that "everything around the dose" is enough to move the number.

What happened

Last year my routine was one test a month, in the first days of the month. At the start of October it was 2.92 — comfortably inside my range. Around the 15th my wife, my daughter and I left for a week in Vienna. Good trip, good food, nothing dramatic. I felt fine the whole time and fine when we came back.

At the start of November I tested again, on schedule: 1.72.

That's not "a bit low". For someone like me it's the dangerous direction — an INR that low means the blood is clotting almost as if I weren't taking the medicine at all. And I had no idea when it had dropped. In Vienna? The week after? I'd spent somewhere between ten days and three weeks outside my range, feeling perfectly well, which is the whole problem with anticoagulation: you don't feel the number.

What followed was a call to my doctor, a correction, and repeat tests until it was back. That was the trip that changed my routine.

My routine now

It's simple, and it's the same for a beach holiday and a two-day business trip:

  1. The morning before I leave, I test. That gives me a known starting point. If the number is already drifting, I'd rather find out at home, near my own doctor and my usual lab, than in a hotel.
  2. The morning after I'm back, I test again. Not a week later at the next scheduled check — the next morning. If the trip moved my INR, I want to know while it's still a small problem.
  3. I log both tests and every dose in the app, with the dates. When I call my doctor, "it was 2.9 on the 14th, 1.9 on the 23rd, and here's every dose in between" is a conversation. "I think something's off?" is not.

Two tests, bracketing the trip. That's the entire method.

Why food is the usual suspect

Warfarin, Sintrom, Marcoumar and the rest of the family all work by interfering with vitamin K, which the body uses to make clotting factors. So how much vitamin K you eat matters — and the point every anticoagulation clinic makes is consistency, not avoidance. Your dose was set against your usual diet. Eat roughly the same amount of green, leafy things every week and the dose keeps fitting. Change the pattern for a week and it may not.

Travel is a week-long change in pattern by definition. I still can't tell you exactly what did it in Vienna — more vegetables than I eat at home, different oils, bigger portions, restaurant food three times a day. Any of those can nudge the number; all of them at once, for a week, can shove it. And it can go either way: more vitamin K than usual pushes INR down, less pushes it up. Mine went down.

Illness is the other one. A stomach bug or a course of antibiotics on a trip can move INR noticeably — that's well documented, and it's a reason to call your doctor rather than wait.

What the two tests buy me

  • A baseline. If I'm 2.7 the morning I leave, I know what "normal" looked like for this trip.
  • An early warning. The morning-after test catches a drift at most a week old — not the three weeks my Vienna drop may have had.
  • A better conversation with the doctor. I'm not guessing. I have two numbers and a complete dose log between them, and they decide what, if anything, to do.

What the two tests do not do: they don't tell me to change my dose. I don't change anything on my own — ever. The tests give my doctor — a vascular specialist who has managed my Sintrom since the surgery — the information; he makes the call. That division is the one rule I never bend, and it's also why the app I built records what the doctor prescribed and never suggests a number.

Small things that help

  • Keep the tablets in hand luggage, in the original box, with a copy of the prescription. Checked bags get lost; a week without tablets is a real emergency.
  • Same lab, every time. INR results from different labs and methods aren't perfectly comparable. My two bracket tests mean something because both come from the same lab I've used for years — the same is true of the numbers in between.
  • Know the name of your medicine in the country you're visiting. Sintrom is acenocoumarol; warfarin is Coumadin in some countries, Marevan in others, Jantoven in the US; Marcoumar is phenprocoumon. If you ever need a pharmacy abroad, the generic name is the one that works.
  • Time zones: an hour's difference, like Vienna, changes nothing for me. For a long-haul trip, ask your doctor or anticoagulation clinic about dose timing before you go — the answer depends on how far you're going and what you take.
  • Write it down. Whatever you do with timing or testing, log it with the date. The log is what makes the post-trip conversation useful.

The honest summary

I can't prevent a trip from affecting my INR. I can make sure I find out quickly, with numbers rather than feelings, and hand the decision to the people whose job it is. Two morning tests bracketing the trip. It's not clever. It's just the thing that would have caught 1.72 the morning I got home from Vienna, instead of ten days later.

If you track your INR and doses in INRythm, the calendar is where the two tests and the doses between them end up — and it exports as a CSV if your doctor wants the list.

Sources

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