by Larry Creswell, M.D.
One topic of discussion that comes up frequently among my athlete friends is the issue of laboratory testing -- specifically, blood testing -- for seemingly healthy athletes. This is an area where there are conflicting opinions among sports medicine and other physicians who care for athletes, but I thought I’d share some of my thoughts. I’ll try to keep things practical.
This issue is actually pretty complicated. In a recent column, I recommended that athletes establish a relationship with a primary care physician. If you have a thoughtful doctor looking after you, you’ll have a sounding board for discussion about the blood tests that may be specific to your circumstances (in terms of overall health) and the tests that might be the most useful to check over time for you specifically.
The blood truly is a window into the body’s health. In some circles in the medical community, the blood is even considered to be an organ itself. Moreover, the entire medical specialty of hematology is devoted to diseases of the blood and the specialties of pathology and laboratory medicine are devoted, in part, to the field of clinical laboratory testing. It’s important to realize that entire books -- or collections of books -- have been devoted to the topic of blood tests, so my synopsis here is abbreviated at best.
Four important concepts deserve mention before we consider specific blood tests.
- Baseline values: There is an excellent introduction to the topic of blood testing for athletes in Chapter 13 of Gordo’s book, Going Long, 2nd ed. That discussion gets at the notion that it’s useful to measure some blood tests as a “baseline.” This is an important concept. Having a baseline set of values for a variety of blood tests can be very helpful down the line if an athlete (or any individual) develops some sort of health problem. These baseline values are also useful when we look for a return to “normal” after some sort of health problem.
- Normal: The second important concept relates to the issue of “what’s normal?” Any laboratory where blood tests are performed will have established a “normal reference range” for any particular test. But the normal range may differ from one laboratory to another, depending upon the exact methodologies that are used to perform a particular test. As a result, what’s “normal” in one laboratory may be slightly abnormal in another.
- Degrees of abnormal: Laboratory values will fall on a spectrum. There is no particular magic to the cut-offs between normal and abnormal values. Keep in mind that slightly abnormal values may not indicate a problem.
- Normal for athletes: The last important concept to keep in mind is that “normal” ranges are established for the entire population -- say, adults as a whole. In a variety of ways, though, athletes are actually very different from the population as a whole. As a result, a particular blood test for an athlete may produce an “abnormal” result (according to the laboratory) that is perfectly understandable (and typical) for a highly trained athlete.
Let’s talk about some of the common -- and useful -- blood tests.
Complete Blood Count (CBC): This is a panel of tests that examine the various blood cells themselves. The three most important tests are:
- White blood cells (WBCs) - The WBC count is generally elevated with inflammation or infection of almost any sort. The WBC count may be low with malnutrition or in situations in which the immune system is depressed. Highly trained endurance athletes, though, may have a low WBC count but which could be considered normal for them.
- Hematocrit - This is a measurement of the fraction of blood volume that is taken up by the red blood cells. In common parlance, this is the “blood count.” When the hematocrit is low, we say that the patient has anemia (which has many potential causes). The hematocrit can sometimes be abnormally high in athletes, particularly if the athlete is dehydrated.
- Platelet count - The platelet is the blood component that is responsible for blood clotting. The platelet count may be high in athletes with dehydration.
The CBC panel also includes measurements of the size of red blood cells that may help distinguish from among several potential causes of anemia.
Basic Metabolic Panel (BMP): This is a panel of seven basic tests.
- Sodium - The sodium may be low in athletes with excess water intake and may be high in athletes with dehydration. Severely low sodium levels may produce nausea, cramping, or neurologic problems. Severely high sodium levels may produce seizure or coma.
- Potassium - Dr. Bob Albright wrote an excellent column here at Endurance Corner about potassium and athletes. Check it out.
- Blood urea nitrogen (BUN) - The BUN is high with kidney failure, muscle breakdown, or dehydration.
- Creatinine - The creatinine is high with kidney failure, muscle breakdown, or dehydration.
- Glucose - The glucose is high with diabetes. To check for diabetes, this test should be performed after an overnight fast. In athletes, the glucose may be somewhat elevated with the stress of exercise.
Comprehensive Metabolic Profile (CMP): This is a panel that includes the BMP and adds approximately seven additional tests.
- Calcium - The calcium may be low with low dietary intake or with excessive loss of calcium (demineralization) from bones.
- Total protein - The total protein may be low with poor nutrition.
- Albumin - The albumin may be low with poor nutrition.
- Alanine amino transferase (ALT) - This is a liver enzyme that may be elevated with hepatitis or other diseases of the liver.
- Aspartate amino transferase (AST) - This is another liver enzyme that may be elevated with hepatitis or other diseases of the liver.
- Alkaline phosphatase - An elevated alkaline phosphatase may suggest liver disease.
- Bilirubin - An elevated bilirubin produces jaundice (yellowing of the skin). The bilirubin may be high due to breakdown of red blood cells or due to liver disease.
Lipid Profile: This is a collection of tests that measure, at a minimum, four different lipid components in the blood.
- Total cholesterol
- Low density lipoprotein - (LDL, or "bad” cholesterol).
- High density lipoprotein - (HDL, or “good” cholesterol). The HDL is typically relatively high in athletes and is often “abnormally” high in well-trained athletes. This shouldn’t cause concern.
The lipid profile is usually checked after a overnight fasting period. We know that abnormally high levels of total cholesterol, LDL, and triglycerides over the long term are associated with heart disease and stroke, so it’s important to discover this problem early, if present, and to make dietary modifications or provide drug therapy. The American Heart Association (AHA) recommends that the lipid profile be checked every five years for people older than 20 years and these tests should be repeated more often for those with abnormal results or with other risk factors for heart disease. I’ll devote an entire upcoming column to the topic of serum lipids and heart disease.
Iron Studies: Iron-deficiency anemia is probably the most common cause of anemia in athletes. Several blood tests are useful for establishing this diagnosis.
- Serum ferritin - This is the most useful test and will be abnormally low with iron-deficiency anemia.
- Serum iron - The serum iron level is usually low with iron-deficiency anemia.
- Total iron binding capacity (TIBC) - The TIBC is usually elevated with iron-deficiency anemia.
When should athletes get these blood tests? I suspect that this question is best answered in consultation with your physician. I usually tell my athlete friends that they should get a CBC and BMP with their annual check-up. I also suggest using the AHA guidelines for checking a lipid profile every five years, provided the results are normal and there are no other heart or vascular conditions. I recommend that any other blood tests be performed, as needed, to evaluate for specific problems that are suspected because of symptoms of one sort or another or because of laboratory abnormalities discovered in the screening CBC or BMP.
Lastly, I’m often asked if one or more blood tests can be used to evaluate for over-training. This is a complicated issue, but my take on things is that, despite much investigation, there is no consensus that any test (or collection of tests) can be used to predict an oncoming state of over-training. This issue has received a lot of attention, so perhaps we could devote an upcoming column to this topic.
Larry Creswell, M.D., is a cardiac surgeon and Associate Professor of Surgery at the University of Mississippi Medical Center in Jackson, Mississippi. He writes the The Athlete's Heart blog and can be reached by e-mail at firstname.lastname@example.org. You can also learn about Larry in his recent Endurance Corner athlete profile.