Should You Work Out Before Getting a Blood Test?

If you're scheduled for bloodwork, you might be wondering whether you need to make changes to your routine including your workouts. While breaking a sweat before a blood test might seem harmless, it can actually affect the accuracy of certain lab results. The good news? Knowing what to avoid and when to exercise can help ensure you get the most reliable information from your test.

What Blood Tests Measure and Why Accuracy Matters

Blood tests are one of the most commonly used tools to assess your overall health. Doctors use them to check everything from blood sugar and cholesterol levels to signs of inflammation, anemia, and organ function. They're also essential for diagnosing conditions like diabetes, heart disease, and even cancer.

Depending on the type of test ordered, you may be required to fast, avoid certain foods, or hold off on specific activities like smoking or exercising. That’s because even small lifestyle factors can influence your body’s internal chemistry and throw off the results.

How Exercise Can Affect Blood Test Results

While regular exercise is undoubtedly beneficial for your health, certain workouts can temporarily alter your blood levels. Here's how physical activity may impact your test findings:

• Blood Glucose Levels
  Fasting blood sugar tests help screen for diabetes or insulin resistance. A 2017 study in the Journal of Exercise Rehabilitation found that moderate aerobic exercise did not affect glucose test results. However, high-intensity exercise can cause your body to produce more glucose in response to stress, leading to elevated readings for up to two hours afterward.

• Red Blood Cell Count
  Exercise especially endurance activities like running can temporarily increase your red blood cell (RBC) count due to fluid loss from sweating. In a 2016 study from the Open Access Journal of Sports Medicine, researchers noted that athletes showed significantly altered RBC levels during and after marathon running, largely due to dehydration. While levels normalize shortly after rest and rehydration, it’s still something to flag to your doctor.

• Cholesterol and Triglycerides
  The same 2017 study also found that short-term exercise doesn’t significantly affect cholesterol readings. However, long-term vigorous activity can improve your HDL (good cholesterol) and reduce triglycerides. That’s great news for your overall health, but you’ll want to avoid skewing short-term results with intense workouts right before a test.

• Inflammation and Enzymes
  Strenuous exercise temporarily elevates inflammatory markers like white blood cells and enzymes like creatine kinase (CK), which can also impact liver function tests (like AST). These levels may take several days to return to normal. If you’ve done a hard workout or participated in an endurance event within the past few days, it’s best to let your healthcare provider know.

When to Skip Your Workout Before a Blood Test

To avoid interfering with your results, consider the following guidelines:

• Avoid high-intensity workouts for at least 24–48 hours before your blood test

• Skip moderate activity for 2–3 hours before your appointment, especially if fasting is required

• Drink plenty of water before the test to help ensure proper hydration

• Let your doctor know if you’ve recently done an intense workout or endurance event

What About Fasting?

Many blood tests require fasting for 8 to 12 hours beforehand—especially those that measure glucose or lipids. During this time, only water is allowed. You should also avoid:

• Eating or drinking anything besides water

• Smoking or chewing gum

• Physical activity, including workouts

Following these recommendations ensures your baseline levels are not artificially influenced by recent food, drinks, or physical exertion.

The Bottom Line

While working out is great for your long-term health, it's best to hit pause on exercise before a blood test. High-intensity or prolonged physical activity can temporarily alter glucose, red blood cell count, inflammation levels, and certain enzymes potentially impacting your results. For the most accurate readings, avoid working out for at least a day or two before your test, and always communicate your recent activity with your healthcare provider.

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