How Exercise Affects the Accuracy or Interpretation of Blood Test Results

Exercise is widely recognised for its profound benefits on overall health and well-being. However, what many people may not realise is that acute exercise, especially within 48 hours before a blood test, can significantly impact certain biomarkers, leading to skewed results.

These temporary changes in areas such as liver enzymes, sex hormones, prolactin, and inflammation markers can complicate the interpretation of blood test data, potentially resulting in misdiagnosis or unnecessary concern or interventions.

For healthcare practitioners and clients alike, understanding how recent physical activity affects blood chemistry is crucial. By identifying and managing the effects of exercise on key markers, clients can better prepare for blood tests, and clinicians can make more informed decisions based on accurate data.

This article delves into how exercise influence various biomarkers and offers practical advice on how to minimise these effects to ensure reliable and repeatable test results.

Let’s have a look at some of the most common imbalances noted on lab tests when someone has exercised intensively in the lead up to the test, especially within 48hours.

Liver and Tissue-Related Enzymes

Acute exercise, especially strenuous or prolonged activity, can cause temporary elevations in enzymes related to muscle and liver tissue damage. These enzymes include Creatine Kinase (CK), Alanine Aminotransferase (ALT), and Aspartate Aminotransferase (AST).

Creatine Kinase (CK)

CK is an enzyme found in muscles, and its levels increase significantly after exercise, particularly when muscle tissue has been stressed or damaged. Even moderate exercise, such as weightlifting, running, or cycling, can lead to a noticeable rise in CK levels within 24 to 48 hours after the activity. Elevated CK may be mistakenly interpreted as cardiac, inflammatory or muscular conditions if recent exercise is not considered.

For this reason, CK levels should be measured after a period of rest to ensure that the results reflect baseline muscle health. We recommend at least 48hours and suggest tracking what training you did in the days prior to that to add context to the interpretation of CK, should it remain elevated.

Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST)

ALT and AST are enzymes primarily associated with liver function, but they are also found in muscle tissue. Acute exercise can lead to the release of these enzymes from damaged muscle cells, temporarily elevating their levels in the bloodstream. This could result in false positives for liver dysfunction, especially if the individual engaged in heavy resistance training or endurance activities, both of which place significant strain on muscle tissues.

This is why resting from vigorous exercise for at least 48 hours before testing is recommended to avoid confounding results.

Sex Hormones

Acute exercise can influence levels of sex hormones, particularly testosterone. The effects can vary depending on the intensity, duration, and type of exercise performed.

Short-term, intense exercise can lead to a temporary increase in testosterone levels, especially in men. This spike is typically seen immediately post-exercise and can last for a few hours. However, prolonged or very intense exercise can lead to the opposite effect, a temporary decrease in testosterone levels. If you have been tested within 48hours of an intensive training session, it is not uncommon to see low or low normal testosterone levels.

In women, intense exercise can also impact estrogen and progesterone levels. These fluctuations may obscure the accurate assessment of baseline hormone levels, leading to misinterpretations of androgen levels, fertility status, or hormonal imbalances.
For accurate measurement, it’s best to avoid strenuous physical activity for 48 hours before testing sex hormones.

Prolactin

Prolactin, a hormone primarily associated with lactation, also plays a role in stress response and hormonal health.

Acute exercise, particularly intense weight training or endurance activities, can cause a transient rise in prolactin levels. This is due to exercise-induced stress, which triggers the hypothalamic-pituitary axis and stimulates the release of prolactin.

Elevated prolactin levels can be misinterpreted as a sign of prolactinoma (a type of pituitary tumour) or other endocrine disorders if recent exercise isn’t accounted for.

Acute elevations in prolactin may also lead to changes in the levels of sex hormones, as noted in the section above.

Ensuring that prolactin levels are measured after a period of rest, ideally with reduced physical exertion for at least 24-48 hours before the test, helps to obtain a more accurate reading.

Inflammation Markers

Exercise-induced inflammation is a normal physiological response to muscle stress and repair. However, measuring inflammation markers too soon after intense exercise can give the impression of underlying chronic inflammation or infection.

C-Reactive Protein (CRP) and Other Inflammatory Markers

CRP is a marker of systemic inflammation and is commonly elevated in response to infection, injury, or chronic inflammatory conditions. However, CRP can also rise temporarily following acute exercise, particularly after high-intensity or endurance activities. Other markers like interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) can similarly increase due to the muscle repair process.

If blood tests are conducted too soon after exercise, elevated levels of these markers might be misinterpreted as signs of acute or chronic inflammation, leading to unnecessary concern or intervention.

A recovery period of 48 hours without strenuous exercise is recommended before testing to allow inflammation markers to return to their baseline levels.

Summary

Exercise, while essential for maintaining health, can have a significant impact on blood test results, especially when performed within 48 hours prior to testing. Key markers such as liver enzymes (CK, ALT, AST), sex hormones (like testosterone), prolactin, and inflammation markers (CRP) can all be temporarily elevated or altered due to acute exercise.

Without proper preparation, these fluctuations can lead to misleading results, potentially causing confusion or incorrect diagnoses. By understanding how exercise influences these biomarkers and following appropriate guidelines, both clients and clinicians can ensure that blood test results more accurately reflect an individual’s true health status.

At Steve Grant Health we understand the importance of accurate blood test results for informed decision making. Our comprehensive testing services not only provide reliable data but also include personalised interpretation and consultation sessions.

With our guidance, you can be confident that your results reflect your true health status, allowing us to work together on tailored solutions that promote your long-term well-being.

Learn more about our testing services:

• Body Composition Test
• Health Assessment
• Digestive Health Assessment
• Athlete Assessment
• Cardiovascular Health Assessment