It sounds like this person spent a lot of time thinking about this but started with a wrong basic assumption. WARFARIN DOES NOT THIN THE BLOOD. Never believe anything that people who think warfarin thins the blood say, they have absolutely no knowledge of how warfarin works. It has nothing whatsoever to do with the viscosity of the blood. Warfarin slows down the ability of the blood to form a clot. This is what is measured on the INR test not how thick or thin the blood is. Warfarin is metabolized in the liver. Our bodies are designed to conserve the essential functions - brain, heart, liver and kidneys. Before the body got cold enough to slow the metabolism of warfarin in the liver, your fingers, toes and ears would probably already have dropped off.
A drop of 0.3 is almost insignificant. The test is simply not that accurate. You could put drops of blood from the same puncture on two different testers and get that much variation.
Red blood cells carry oxygen. More are produced in response to the cells in the body not having enough oxygen. There may be some small effect from prolonged exposure to cold but most people have houses heated or cooled to 70 to 80 degrees year round. Just looking out a window at snow or even shoveling a sidewalk will not change your INR.
Red blood cell production takes days. You cannot see any difference in a flight of even a long distance such as to Australia. What might happen on a long flight is that you become dehydrated. This will literally thicken the blood because there is less water not more red cells. Once you get rehydrated they red blood cell count would be back to where it was prior to the flight.
This person would probably make a good science fiction writer.
