As dietitians seek ways to accurately determine nutritional status based on lab results, C-reactive protein often becomes part of the conversation. Does this lab test serve any usefulness for dietitians?
C-reactive protein (also known as CRP) is an acute-phase protein that is synthesized in the liver. Under normal circumstances, it is very low—<0.6 milligrams (mg)/deciliter (dL) (Mahan and Escott-Stump). During systemic inflammation, levels of CRP increase in the blood. An elevated CRP can indicate that inflammation is present, but cannot pinpoint the location of the inflammation or diagnose a condition.
The following conditions also may show an elevated CRP:
- Connective tissue disease
- Heart attack
- Inflammatory bowel disease
- Pneumococcal pneumonia
- Rheumatoid arthritis
- Rheumatic fever
Sometimes CRP is useful in determining if inflammation is reduced or if specific treatments, such as medications for rheumatoid arthritis, are having their intended effects. CRP is not helpful in assessing protein or calorie needs, but may serve as an indicator of increased nutrient needs (American Dietetic Association).
A more sensitive indicator of inflammation is high sensitivity C-reactive protein, also known as hs-CRP. Hs-CRP carries predictive power for coronary events (National Heart, Lung, and Blood Institute and the National Institutes of Health; American Heart Association). Inflammation-related damage to the arteries that is caused by smoking, hypertension, atherogenic lipoproteins, and hyperglycemia contribute to plaque formation and plaque disruption, resulting in formation of blood clots.
Studies show that the higher the hs-CRP levels, the higher the risk of having a heart attack (MedlinePlus).
- A hs-CRP <1.0 mg/dL indicates low risk for developing cardiovascular disease (CVD)
- A hs-CRP score of 1.0-3.0 mg/dL indicates an average risk for developing CVD
- A hs-CRP score of >3.0 mg/dL places a person at high risk for developing CVD
CRP levels also are elevated (>3 mg/dL) in people with angina, stroke, and peripheral vascular disease (Mahan and Escott-Stump).
Hs-CRP testing is not recommended routinely, but is recommended as an independent predictor of coronary risk. Some patients who have an elevated cardiovascular risk score based on a Framingham global risk assessment may benefit from a CRP test (Pearson et al). A number of global risk assessments based on the Framingham study are available for use by clinicians. Information on these different assessments is found at http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=14687264.
The American Heart Association suggests the following guidelines for adding CRP to a global risk assessment for heart disease (Pearson et al):
- If CVD risk score is <10% in 10 years, no CRP test is warranted
- If CVD risk score is 10%-20% in 10 years, a hs-CRP test can help predict a CVD or stroke event, and help direct further evaluation and therapy
- If CVD risk score is high (>20% in 10 years) or heart disease or stroke is present, the patients should receive treatment regardless of the hs-CRP levels.
Implications for dietetics practitioners
A routine CRP test is an indicator of generalized inflammation, but cannot pinpoint or diagnose specific conditions or help determine nutritional needs of a patient. Hs-CRP, used in conjunction with global assessment of cardiovascular disease risk, can help a dietitian develop nutrition interventions that are appropriate for a patient’s level of CVD risk.
American Dietetic Association. ADA Nutrition Care Manual®. Available at: www.nutritioncaremanual.org. Accessed May 6, 2009.
American Heart Association. Inflammation, heart disease and stroke: the role of C-reactive protein. Available at: http://www.americanheart.org/print_presenter.jhtml?identifier=4648. Accessed May 6, 2009.
Mahan LK, Escott-Stump S. Krause’s Food and Nutrition Therapy. 12th ed. St Louis MO: Saunders/Elsevier; 2008.
MedlinePlus Medical Encyclopedia. C-reactive protein. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/003356.htm. Accessed May 6, 2009.
National Heart, Lung, and Blood Institute and the National Institutes of Health. Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III): Final Report. NIH Publication 02-5215. Available at: http://www.nhlbi.nih.gov/guidelines/cholesterol/atp3full.pdf. Accessed May 6, 2009.
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 [serial online].2003;107:499-511. Available at: http://www.americanheart.org/downloadable/heart/1043429236960hc0303000499.pdf. Accessed May 13, 2009.
Ridker PM, Wilson PWR, Grundy SM. Should C-reactive protein be added to metabolic syndrome and to assessment of global cardiovascular risk? Circulation [serial online]. 2004;109:2818-2825. Available at: http://circ.ahajournals.org/cgi/content/full/109/23/2818?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Should+C+Reactive+Protein+
Be+Added+&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT. Accessed May 6, 2009.
Sheridan S, Pignone M, Mulrow C. Framingham-based tools to calculate the global risk of coronary heart disease. J Gen Intern Med [serial online]. 2003;18:1039-1052. Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=14687264. Accessed May 13, 2009.
Review Date 8/09