Should you exercise before a blood test?
The short answer
Everyday activity is fine, but try to skip hard or unusual workouts for 2 to 3 days before your blood draw. Strenuous exercise can temporarily raise CK, AST, ALT, creatinine and white blood cells and lower testosterone, which can make normal results look abnormal.
What to do
- Stick to light activity, like walking, for 2 to 3 days before your draw.
- If you did an unusually hard weightlifting session, consider waiting about a week before a liver panel or CMP.
- Don't train hard on the morning of your test.
- For fasting insulin, avoid strenuous exercise the night before; for the Cardio IQ lipid panel and NMR LipoProfile, avoid intense exercise the day before.
- Tell your clinician about recent hard training when you review your results.
Which results it changes
| Marker | Effect | How long |
|---|---|---|
| Creatine kinase (CK)[2][3] | Rises sharply after hard or unaccustomed exercise | Still raised at least 7 days after a heavy lifting session; still rising 24 hours after a marathon |
| AST and ALT[2] | Can rise to levels that look like liver injury | At least 7 days after unaccustomed heavy weightlifting |
| Creatinine[3] | Rises after a marathon; creatinine-based eGFR reads lower | Peaked right after the race and was lower 24 hours later |
| White blood cells (WBC)[4] | Rise after a single bout of exercise | Timing not well defined in our sources |
| Free testosterone[5] | Falls after exhausting endurance exercise | Still lower at 24–48 hours; about 72 hours to return to baseline |
| Cortisol[5] | Rises right after exhausting exercise, then can dip below baseline | About 48 hours to return to baseline |
Why a workout can change your results
Many lab values shift with exercise. How much depends on the type, intensity and length of the workout, your training level, and how long you rested before the draw.
Lab medicine experts point out that results outside the reference range in active people often reflect recent hard exercise or normal adaptation to training rather than disease. Knowing this helps you and your clinician avoid misreading a result.
Muscle and liver enzymes: CK, AST and ALT
In one study, 15 healthy men who were not used to weightlifting did a 1-hour lifting session. Their AST, ALT, LD, CK and myoglobin rose significantly and stayed raised for at least 7 days. GGT, alkaline phosphatase and bilirubin stayed normal.
The researchers concluded that intense muscular exercise should be considered as a cause of unexplained raised liver tests. AST and ALT are part of the CMP and the liver panel. If you start a new or much harder training plan, a week's gap before these tests gives a cleaner picture.
Creatinine and kidney numbers
In a study of 22 marathon runners, 82% had a rise in serum creatinine large enough to meet the criteria for acute kidney injury. Creatinine peaked right after the race and was lower again a day later, while CK kept rising.
Creatinine is part of the CMP, the BMP and the kidney panel, and eGFR is calculated from it. A draw soon after a long, hard effort can make your kidney numbers look worse than your usual baseline.
White blood cells and hormones
A single bout of exercise causes a striking rise in white blood cells in the blood, as immune cells move around the body. That can push up the white blood cell count on a CBC.
Hormones shift too. After about 97 minutes of hard treadmill running, trained men had higher cortisol right after exercise and lower free testosterone. Free testosterone was still lower 24 and 48 hours later, and the authors estimated about 72 hours to return to baseline. If you are testing testosterone, avoid a long, exhausting session in the days before.
What counts as light activity
The studies above tested hard efforts: an hour of heavy lifting, a marathon, or a long run at threshold pace. Normal daily activity, like walking to the lab or light chores, is not what they measured.
If you train regularly, try to test at a similar point in your week each time, so your results compare like with like.
Frequently Asked Questions
More on preparing
Sources
- Sanchis-Gomar F, Lippi G. Physical activity - an important preanalytical variable. Biochem Med (Zagreb). 2014;24(1):68-79. doi: 10.11613/BM.2014.009. PMID: 24627716. PubMed
- Pettersson J, Hindorf U, Persson P, Bengtsson T, Malmqvist U, Werkström V, Ekelund M. Muscular exercise can cause highly pathological liver function tests in healthy men. Br J Clin Pharmacol. 2008 Feb;65(2):253-9. doi: 10.1111/j.1365-2125.2007.03001.x. PMID: 17764474. PubMed
- Mansour SG, Verma G, Pata RW, Martin TG, Perazella MA, Parikh CR. Kidney Injury and Repair Biomarkers in Marathon Runners. Am J Kidney Dis. 2017 Aug;70(2):252-261. doi: 10.1053/j.ajkd.2017.01.045. PMID: 28363731. PubMed
- Simpson RJ, Kunz H, Agha N, Graff R. Exercise and the Regulation of Immune Functions. Prog Mol Biol Transl Sci. 2015;135:355-80. doi: 10.1016/bs.pmbts.2015.08.001. PMID: 26477922. PubMed
- Anderson T, Lane AR, Hackney AC. Cortisol and testosterone dynamics following exhaustive endurance exercise. Eur J Appl Physiol. 2016 Aug;116(8):1503-9. doi: 10.1007/s00421-016-3406-y. PMID: 27262888. PubMed
Content reviewed for accuracy by the JustLabs editorial team.
Educational information, not medical advice. Don’t stop or change a prescribed medicine without talking to your prescriber. If your lab order gives different instructions, follow your lab order.