Is the Blood of a Runner Different?

A small amount of any of your body fluids provides massive information. These tests will report a number and tell you whether it falls within the normal range.


But what is the normal range? This “normal range” is based on hundreds of thousands of tests of people. People who are old and young, male and female, sick and healthy, runners and non-runners. Top marathon runners have different lab values than sedentary folks, even moderate runners can cause changes in commonly measured lab tests, you should be aware of the common variations and those that should raise a red flag. We will look at some of these tests, tell you which ones you should worry about and which ones can be considered normal. If you have other tests you want to discuss, let us know in the comments section.


Anemia is seen in the blood test with a decrease in hemoglobin or in red blood cells. The most common complain with mild anemia is of being chronically tired or it may not cause any symptoms at all but still impair performance. The current consensus is that runners commonly experience mild anemia mainly influenced by iron deficiency.

There are many types of anemia that a runner can suffer:

Runner’s Anemia

This is considered an uncommon cause of anemia. It is the result of an increase of plasma volume and rupture of red blood cells due to the continuous pounding of feet on the pavement, it usually turns out with blood detected in urine tests (not visible to the naked eye) and may also run with gastrointestinal blood loss (again, detected only in tests) due to ischemia during long distance running.


This type of anemia runs with macrocytic anemia (anemia with big red cells). If your doctor is not aware you are an avid runner, she may be willing to run more invasive tests to rule out other potentially dangerous diagnosis.


Iron Deficiency Anemia

Is the most commonly encountered anemia in runners and non-runners. It basically can be caused by too little intake or too much output.

popeyeIf you are diagnosed with iron deficiency anemia and your problem is your iron intake, you should correct it by eating more meat, iron-fortified cereals or leafy greens. In more severe cases it may be necessary to take iron supplements.

An increased output in runners may be secondary to many causes and warrants further investigation. One of these causes specific to runners is gastrointestinal blood loss known to be produced by ischemia of the intestines during long runs.

Strenuous exercise

Having a blood test up to 72 hours after an extreme run will probably show abnormal results. It is best to wait a few days to have your blood analyzed. If you believe your tests are altered due to exercise, mention it to your doctor as it may be a good idea to repeat these tests after a few days before turning to more invasive testing or treatment. Lets look at some of these alterations in detail.

Urine Test

It may be positive for blood after a long run, a small amount of bleeding from the bladder or kidneys results afterwards. This is not usually visible to the naked eye but will be detected by the lab. If it does not resolve within 24 to 72 hours further evaluation is necessary.

Protein may also be detected in a urine test, and should clear within 24 to 48 hours.

Myoglobin and CK

A small elevation of blood CK and myoglobin is expected in most runners after exercise. A greater elevation may point to a condition known as rhabdomyolysis (degradation of muscle tissue), it should be taken seriously as it may cause renal failure and can even be fatal.

BUN and Creatinine

milkThese are markers of kidney function. BUN is usually quite elevated on dehydration and Creatinine can also elevate mildly, if you know you were dehydrated while you took the test all you have to do is get hydrated again.


It is used to evaluate liver function, but this enzyme is also present in skeletal muscle, so its levels will elevate after exercise. Check the other tests for liver function (ALT, GGT, Alkaline phosphatase…) to make sure those are not elevated.

Blood Cells

There is usually a transient increase in white blood cells and platelets, which can be considered normal after exercise.

Vitamin D

Vitamin D is a steroid hormone produced by your own body in Sunresponse to sunlight. If you are a milky white runner living in London there is a good chance that you are on the low side. Athletes in general may be more susceptible to Vitamin D deficiency and that may or may not hurt performance. This hormone has been linked to skeletal muscle performance, increased recovery and increased testosterone, however, it is hard to prove that Vitamin D on its own causes all these benefits as there may be many factors involved.


Inflammation is measured by various markers, including C-reactive protein, TNF-alpha and Erythrocyte Sedimentation Rate which are very specific markers that can provide an overall picture of inflammation.

It is generally regarded as a bad thing, but you need a certain amount of inflammation to make improvements, the muscle has been hurt and needs to repair and rebuild.  As a general rule, a small acute inflammation in a runner is probably a good thing, while chronic inflammation should set off a red flag.


Keep in mind that there are multiple causes of lab abnormalities and we only covered a few. Always follow the recommendations of your healthcare provider.

Knowing what your inner body looks like is only useful if you can make changes to it, and you will only know it changes if you repeat the test, always take into account that it is hard to prove that a change in a body marker will relate with a better performance. Let us know in the comments what you think.

ConditionMarkersMeaning in Runners
AnemiaHb, HCTNo symptoms, fatigue, decreased performance
UrineBlood, proteinmay be present for a couple days after extreme runs
Muscle proteinsMyoglobin, CKsmall amount may be ok. Large amount is dangerous
HydrationBUN, CrDehydration (amongst other things)
LiverASTElevated after long runs, check the other liver enzymes
Blood CellsWBC, plateletssmall elevation after runs
VitaminVitamin Drelated to performance???
InflammationCRP, TNF-a, ESRsmall and acute ok. large and chronic not ok
Common alterations in lab tests. This is only a general guide, always check with your health provider.

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