C-reactive protein above or below normal: causes in athletes and what to do
CRP above normal is one of the most frequent "alarming" findings in check-ups of active people. But in an athlete this protein can rise both after an ordinary hard workout, and because of an unnoticed cold, and because of a serious illness. The editorial team examines how to distinguish a physiological rise from a pathological one, what a very low CRP means and what plan of action is reasonable in each situation.
How to read the degree of increase
It is useful to assess CRP values not by the principle of "normal — not normal", but by degree. A small increase within a few milligrams per liter is most often linked to chronic low-grade inflammation: excess fat mass, smoking, poor sleep. In the categories of Pearson et al. (2003) hs-CRP over 3 mg/L corresponds to higher cardiovascular risk.
Values from 10 to a few tens of mg/L usually indicate an active inflammatory process: a viral infection, injury, exacerbation of a chronic illness or a recent exhausting competition. In this range hs-CRP is no longer used for assessing cardiac risk.
Values over 50–100 mg/L are more often linked to bacterial infections, significant injuries, systemic inflammatory diseases. Such a result requires a search for the cause, not waiting for it to "go away on its own".
It is important to remember that the boundaries between categories are conditional, and CRP is a nonspecific marker. It shows the presence and approximate intensity of inflammation, but not its source.
Sports causes of increase
The most frequent sports cause is recent exhausting exertion. After a marathon, ultramarathon, long-distance triathlon or multi-day race, CRP rises with a peak approximately a day or two later and returns to baseline within a few days. Studies of blood values after a marathon (Kratz et al., 2002) demonstrate how noticeably inflammatory and muscle markers change even in healthy runners.
A significant rise can be caused by unusual eccentric exertion — downhill running, a large number of jumps, a new strength workout with emphasis on the negative phase. Damage to muscle fibers triggers local inflammation, and the liver responds with the synthesis of CRP.
Injuries — sprains, bruises, fractures, the postoperative period — also raise CRP. If, against a background of injury, the level rises again after an initial decrease, a doctor may suspect an infectious complication.
Finally, chronically insufficient recovery, energy and sleep deficit can maintain a moderately elevated background. However, the consensus on overtraining (Meeusen et al., 2013) emphasizes: CRP is not a diagnostic marker of this syndrome, and conclusions are drawn only from the totality of symptoms, performance and the exclusion of other causes.
- Marathons, ultra-distances, multi-day competitions.
- Unusual eccentric exertion.
- Injuries and operations.
- Chronic deficit of sleep and energy.
Medical causes of increase
Infections are the most frequent medical cause of an increase in CRP. Respiratory infections, sinusitis, urinary tract infections, dental foci can raise the level even if the symptoms are barely noticeable. Training against a background of an active infection, especially with fever, is associated with the risk of complications, in particular myocarditis.
Autoimmune and inflammatory diseases — rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease — often debut at a young age and can masquerade as "sports" pain in the back or joints. Persistently elevated CRP together with morning stiffness or night pain is a reason to consult a rheumatologist.
A chronic low-grade increase is linked to visceral obesity, insulin resistance, smoking, sleep apnea. For athletes of heavy weight categories and veteran athletes this is an important signal regarding cardiovascular risk.
Separately worth mentioning is the effect of hormonal preparations: oral estrogens raise CRP. The use of anabolic steroids outside medical supervision is associated with numerous risks for the cardiovascular system (Pope et al., 2014), so in people who use them any risk markers should be assessed especially carefully together with a doctor.
| Situation | Typical CRP | What to do |
|---|---|---|
| 1–3 days after a marathon | May be noticeably elevated | Repeat in 1–2 weeks at rest |
| A cold without fever | Moderate increase | Reduce exertion, repeat after recovery |
| Fever, pain, high figure | High | See a doctor, stop training |
| Persistently 3–10 mg/L at rest | Moderate chronic increase | Assess body mass, sleep, smoking, cardiac risk |
| Persistent increase + pain in joints, back | Variable | Consultation with a rheumatologist |
Low CRP: are there problems
A low or undetectable CRP level is usually a good sign. For hs-CRP a value below 1 mg/L corresponds to the lowest category of cardiovascular risk. In trained people with normal body mass such results occur often, which is consistent with data on the anti-inflammatory effect of regular physical activity (Kasapis, Thompson, 2005).
Statins, some other medications and weight reduction also lower CRP. In the JUPITER study (Ridker et al., 2008) rosuvastatin lowered both LDL and hs-CRP.
The only practical trap of low CRP is false reassurance. Some inflammatory conditions, in particular systemic lupus erythematosus without serositis, can proceed with normal CRP, while the ESR rises. Also, in the early hours of an infection CRP has not yet had time to rise. Therefore a normal result with pronounced symptoms does not rule out illness.
Immunosuppressive drugs, in particular IL-6 blockers, suppress the synthesis of CRP and make it an unreliable marker of infection. For people on such therapy a doctor assesses the condition by other signs.
Algorithm of action
The first step with elevated CRP is to assess the circumstances: whether there was exhausting training, a competition, an injury or signs of infection in the last 1–2 weeks. If so, and well-being is normal, the test is repeated after 1–2 weeks of a calm regimen.
The second step is an assessment of symptoms. Fever, chest pain, shortness of breath, palpitations, joint pain and swelling, weight loss, night sweats are a reason to see a doctor without delay. With fever and systemic symptoms training should be stopped until an examination.
The third step — with a persistent moderate increase at rest, it is worth reviewing lifestyle factors: fat mass, sleep, smoking, nutrition, and also assessing cardiovascular risk together with a doctor (lipid profile, blood pressure, glucose).
The fourth — interpret other tests taking CRP into account: with inflammation ferritin may be falsely normal or elevated, and iron and zinc falsely reduced. Conclusions about deficiencies are better drawn when CRP has normalized.
Editorial conclusions
Elevated CRP in an athlete is often explained by recent exhausting exertion, injury or a mild infection, so the key is a repeat test under standard conditions.
A persistent increase at rest requires a search for the cause — from excess fat mass and poor sleep to autoimmune diseases.
Low CRP is usually a favorable sign but does not rule out illness with pronounced symptoms.
We also recommend reading our materials on what the C-reactive protein test shows, on the ESR and on signs of overtraining in laboratory indicators.
References
- Pearson TA, Mensah GA, Alexander RW, et al. Markers of inflammation and cardiovascular disease: application to clinical and public health practice: a statement for healthcare professionals from the Centers for Disease Control and Prevention and the American Heart Association. Circulation. 2003;107(3):499–511.
- Pepys MB, Hirschfield GM. C-reactive protein: a critical update. J Clin Invest. 2003;111(12):1805–1812.
- Kasapis C, Thompson PD. The effects of physical activity on serum C-reactive protein and inflammatory markers: a systematic review. J Am Coll Cardiol. 2005;45(10):1563–1569.
- Kratz A, Lewandrowski KB, Siegel AJ, et al. Effect of marathon running on hematologic and biochemical laboratory parameters, including cardiac markers. Am J Clin Pathol. 2002;118(6):856–863.
- Meeusen R, Duclos M, Foster C, et al. Prevention, diagnosis, and treatment of the overtraining syndrome: joint consensus statement of the European College of Sport Science and the American College of Sports Medicine. Med Sci Sports Exerc. 2013;45(1):186–205.
- Ridker PM, Danielson E, Fonseca FA, et al. Rosuvastatin to prevent vascular events in men and women with elevated C-reactive protein. N Engl J Med. 2008;359(21):2195–2207.
- Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
Andriy Melnyk
A strength-sports coach and author of programs for beginner and intermediate levels. Writes about training planning.
