White blood cells above or below normal: causes in athletes and what to do

On receiving a test with a note of «above normal» or «below normal» next to white blood cells, many athletes immediately think of a hidden infection or a «run-down» immune system. In reality the range of causes is much broader — from a morning training session before blood is drawn to genetic features. The editorial team has systematized the most common causes of deviations and prepared a step-by-step plan of action.

First — assess the test itself

Before looking for the cause of a deviation, it is worth finding out which part of the differential exactly has changed. Leukocytosis at the expense of neutrophils and leukocytosis at the expense of lymphocytes are entirely different situations, as are leukopenia due to a decrease in neutrophils or lymphocytes. Therefore the first thing to do is look at the absolute numbers of each cell type.

The second question is the conditions under which the blood was drawn. Exertion during the previous day, emotional strain, smoking, lack of sleep and dehydration are able to shift the result. Intense training raises neutrophils for several hours and temporarily lowers lymphocytes, so a test «after a morning run» often looks like an inflammatory one.

The third is how the person feels. Fever, sore throat, cough, joint pain, rash and enlarged lymph nodes help the doctor understand whether it is a matter of infection. A deviation without any symptoms more often has a physiological or laboratory explanation.

Finally, it is worth comparing with previous tests. In some people the white blood cell count stays near the lower or upper limit for years — that is their individual norm. A new deviation from the usual level is far more informative than a formal exit beyond the limits of the form.

Why white blood cells are elevated

Leukocytosis is most often a reaction, not a disease. The body mobilizes immune cells in response to stress, infection, tissue damage or the action of hormones. In athletes, specific causes related to training and injuries are added to the «classic» ones.

Corticosteroids are worth mentioning separately. Injections into joints or tendon sheaths, tablet courses for injuries or asthma change the differential: neutrophils rise, eosinophils and lymphocytes fall. This effect can last several days and does not mean inflammation.

Significant injuries, operations, burns, and also severe muscle damage (for example, rhabdomyolysis after extreme exertion) are also accompanied by leukocytosis. In that case the test is assessed together with creatine kinase, kidney indicators and how the person feels.

A very high white blood cell count, the presence of immature forms (blasts) in the smear, a combination with anemia or reduced platelets — these are no longer «sports» causes, and here an urgent consultation with a hematologist is needed.

Why white blood cells are reduced

Leukopenia is most often associated with a decrease in neutrophils (neutropenia) or lymphocytes (lymphopenia). A short-lived decrease after a viral infection is an ordinary situation that passes within a few weeks. Persistent and pronounced decreases are of interest.

• Viral infections:influenza, COVID-19, mononucleosis and others can temporarily lower neutrophils and lymphocytes.
• Benign ethnic neutropenia:in some people of African and Middle Eastern descent the neutrophil count is constitutionally lower, associated with a variant of the DARC gene (Duffy-null), and does not increase the risk of infections (Reich et al., 2009).
• Medications:some antibiotics, antithyroid, anticonvulsant and other drugs can cause neutropenia.
• Chronic energy deficiency:prolonged undereating against a background of large training volumes suppresses the bone marrow and hormonal regulation.
• Deficiency of vitamin B12, folate, copper:usually together with changes in other blood lineages.
• Autoimmune conditions and blood diseases:require examination by a specialist.

Relative energy deficiency in sport (RED-S) deserves special attention. The IOC consensus (Mountjoy et al., 2018) describes how a shortage of energy disrupts the work of many systems, including the immune one. Athletes who limit calories for a long time for «cutting» or a weight category fall ill more often and recover more slowly.

As for training itself: in some highly qualified endurance athletes a white blood cell count near the lower limit of normal has been described at rest. This is usually not accompanied by frequent infections and is considered a feature, but the final conclusion is made by a doctor after ruling out other causes.

Warning signals and a plan of action

Most small deviations require only a correct repeat test. However, there are situations when one cannot wait. A high fever against a background of pronounced neutropenia is an emergency, because the body poorly restrains a bacterial infection.

1. Check whether there was training, illness, stress, or intake of corticosteroids or other medications before the test.
2. Repeat the complete blood count with a differential in 1–3 weeks, after a day without intense exertion, in the same laboratory.
3. If the deviation persists — see a general practitioner; if necessary they will order a blood smear, CRP, ferritin, vitamin B12, folate, tests for viruses.
4. In the case of pronounced changes or a combination with anemia or thrombocytopenia — a consultation with a hematologist.

Seek help urgently if a fever, a severe sore throat or ulcers in the mouth appear against a background of low white blood cells, or if very high white blood cells are combined with night sweats, weight loss, enlarged lymph nodes, bruises.

Restoring immune balance in an athlete

When serious causes have been ruled out and the deviations are explained by exertion, stress or energy deficiency, correcting the regimen comes to the fore. The position stand on exercise immunology (Walsh et al., 2011) singles out a number of factors that increase the risk of infections in athletes, and most of them can be controlled.

The most important are a sufficient energy value of the diet and carbohydrates during periods of large volumes, full sleep, a gradual increase in load without sharp jumps, hand hygiene during camps and competitions, and vaccination on schedule. These measures are enough for most people.

Persistent deviations combined with a drop in results, chronic fatigue, sleep disturbance and frequent illnesses may be part of overtraining syndrome. The ECSS and ACSM consensus (Meeusen et al., 2013) emphasizes that there is no single laboratory marker of this condition, and the diagnosis is made after ruling out other causes.

«Immunostimulants» and supplements do not replace the search for a cause. The editorial team advises discussing with a doctor the appropriateness of vitamin D, zinc or probiotics only in connection with a specific deficiency or situation, and not as a way to «raise white blood cells» on the test.

Editorial conclusions

Deviations of white blood cells in an athlete are most often explained by exertion on the eve of the test, a past infection or medications, so the first step should be a correct repeat test.

One should assess the absolute numbers of individual cell types and the dynamics, not just the total count. Persistent and pronounced changes, especially with symptoms, are grounds for seeing a doctor.

When serious causes have been ruled out, the best «immunomodulator» is sufficient nutrition, sleep and sensible planning of loads.

We also recommend reading our materials on what a white blood cell test shows, on platelets above or below normal, and on relative energy deficiency in sport.

References

1. Walsh NP, Gleeson M, Shephard RJ, et al. Position statement. Part one: Immune function and exercise. Exerc Immunol Rev. 2011;17:6–63.
2. Pedersen BK, Hoffman-Goetz L. Exercise and the immune system: regulation, integration, and adaptation. Physiol Rev. 2000;80(3):1055–1081.
3. Mountjoy M, Sundgot-Borgen JK, Burke LM, et al. IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med. 2018;52(11):687–697.
4. Meeusen R, Duclos M, Foster C, et al. Prevention, diagnosis, and treatment of the overtraining syndrome: joint consensus statement of the ECSS and the ACSM. Med Sci Sports Exerc. 2013;45(1):186–205.
5. Reich D, Nalls MA, Kao WH, et al. Reduced neutrophil count in people of African descent is due to a regulatory variant in the Duffy antigen receptor for chemokines gene. PLoS Genet. 2009;5(1):e1000360.
6. Schwellnus M, Soligard T, Alonso JM, et al. How much is too much? (Part 2) International Olympic Committee consensus statement on load in sport and risk of illness. Br J Sports Med. 2016;50(17):1043–1052.