Foods that are high in vitamin K such as spinach can affect your INR levels, according to Drugs.com. People who are taking the drug warfarin, also known by the trade name Coumadin, should be especially careful to monitor their intake of vitamin K-rich foods.
Dark green, leafy vegetables have high levels of vitamin K. Some foods to be aware of include broccoli, collard greens, kale, spinach and Brussels sprouts. Foods with lower amounts of vitamin K include lettuce, cabbage, blueberries, kiwi, peas and asparagus. Multivitamins and other supplements may also contain vitamin K, according to Drugs.com.
An INR test determines how quickly the blood clots, says Drugs.com. Warfarin, a blood thinner, makes it harder for the blood to clot. When patients change their vitamin K intake, the effectiveness of the medication changes. If there is a increase in vitamin K intake, the blood can clot too quickly and may cause dangerous clotting in the body. If there is a decrease in vitamin K intake, the blood can clot too slowly, and potentially dangerous bleeding can result.
Patients taking warfarin do not need to avoid foods rich in vitamin K, but they should be careful to keep their vitamin K intake consistent from day to day, according to Drugs.com.