Medical Q&As


I am on long-term warfarin treatment. My blood is tested regularly to measure the clotting time. Does the sun affect the clotting time?

People on long-term warfarin therapy undergo regular blood testing to establish if the clotting time is appropriate for their condition. The measure that is used is known as the International Normalised Ratio or INR. Clotting times can be prolonged by alcohol, aspirin, non-steroidal ant inflammatory drugs, drugs for controlling blood glucose levels and the anti-ulcer drug cimetidine. I am not aware of any evidence that intense heat has any effect on the INR.