Can You Exercise Before a Blood Test?

It is important to let your doctor know if you exercise before a blood test as it can affect some of the findings, including blood glucose levels, inflammatory markers and cholesterol readings. Find out when is the best time to exercise before a blood test to get accurate results.

A blood test is a very common screening tool that looks at your overall health. Your doctor may order a blood test to check for diseases and health conditions, especially if you're getting ready for surgery or experiencing unusual symptoms, says the U.S. Department of Health and Human Services.

These tests look at your risk factors for heart disease and screen you for conditions like cancer, diabetes, anemia and coronary heart disease. A sample of blood is taken either through a finger prick or by using a needle. It is a quick procedure that results in minimal discomfort.

Doctors will use the results of a blood test to diagnose medical conditions, but they may take into consideration other factors as well. They use information from your vital signs, such as blood pressure and pulse, as well as your signs and symptoms, to get the complete picture and make an accurate diagnosis.

To get ready for a blood test, there are some things you should avoid to get the most accurate results. Many people don't realize that what they eat or how soon they exercise before a blood test can affect the results.

If you are having a glucose test to rule out diabetes, you will need to fast for eight to 12 hours before the test, per the U.S. National Library of Medicine. This kind of test will measure your blood sugar levels.

Lipid tests, which measure your levels of triglycerides and cholesterol, also typically require you to fast for eight to 12 hours beforehand.

During a fast, you cannot eat or drink anything besides water. The U.S. National Library of Medicine says that when you are fasting, you should also avoid smoking, chewing gum and exercising before a blood test to ensure the accuracy of your results.

It is fairly easy to see how eating and drinking can affect your blood tests, but what about exercise?

Fasting glucose tests measure your blood sugar and may help diagnose diabetes. A December 2017 study in the ‌Journal of Exercise Rehabilitation‌ (JER) found that doing moderate-intensity aerobic exercise does not affect the blood test results.

High-intensity exercise, however, may cause an increase in glucose production and show high blood sugar levels for one to two hours. Avoid high-intensity exercise for at least two hours before your bloodwork to make sure you get accurate results.

Regular exercise will increase the number of red blood cells (RBC) in the blood. A low RBC count may indicate anemia and/or iron deficiency. In a small study published in the ‌Open Access Journal of Sports Medicine‌ (OAJSM) in April 2016, which looked at blood markers before, during and after a two-day marathon, RBC was significantly higher during the race and below baseline after the race. It returned to normal after the race.

Researchers attribute some of these findings to dehydration from sweating during the run. If you have exercised before your test, make sure you drink water and let your doctor know.

The JER study looked at how exercise affects lipids or total blood cholesterol levels and found that short-term exercise did not affect these values. However, vigorous physical activity for more than three days had a positive effect on high-density cholesterol (HDL) and triglycerides.

Marathon runners can have higher levels of inflammatory markers during strenuous runs, including high white blood cells, but these levels return to normal afterward, per the OAJSM study.

In addition, the OAJSM study points out that blood levels of the muscle enzyme creatine kinase (CK) and the liver function test AST will be higher after exercise. These levels take several days to a week to return to normal.

Stay on the safe side and refrain from doing high-intensity exercise a few days before bloodwork. Keep your doctor informed of your physical activity level, especially if you work out regularly.