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Inflammation
C-reactive protein (CRP)
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A hepatic acute-phase protein that rises within 6 to 8 hours of inflammation or tissue injury and falls quickly once the stimulus resolves. It is more dynamic than the ESR and is used to detect and monitor inflammation and infection.
Reference interval
| Conventional (mg/L) | SI (mg/L) | |
|---|---|---|
| Adults | < 5 (upper limit) mg/L | < 5 (upper limit) mg/L |
Specimen: Serum or heparinised plasma · Conventional × 1 = SI
Causes of high values
Bacterial infection and sepsis (often above 100 mg/L), tissue injury and surgery, myocardial infarction, rheumatoid arthritis and other inflammatory diseases, inflammatory bowel disease, pancreatitis, malignancy, pulmonary embolism. Viral infections usually give lower values.
Causes of low values
Low values are normal. A normal CRP in active lupus erythematosus or ulcerative colitis despite inflammation is a recognised pattern, and severe liver failure can limit production.
Pre-analytical and method notes
Many laboratories use an upper limit of 5 mg/L (some 10 mg/L), and units may be mg/L or mg/dL, so check the report. High-sensitivity CRP (hs-CRP) assays quantify values below 5 mg/L and are used for cardiovascular risk stratification, where under 1 mg/L is considered low risk; hs-CRP is only valid in the absence of acute inflammation. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. Elsevier — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
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