Comparison · Medical test vs Medical test
CRP vs ESR
Both are 'inflammatory markers', and they are often ordered together, but they measure different things at different speeds. CRP is a single protein that rises and falls within days; the ESR is a physical property of blood that changes over weeks and is pushed up by many things besides inflammation.
| Aspect | CRP test | ESR (erythrocyte sedimentation rate) |
|---|---|---|
| What is measured | Concentration of C-reactive protein, an acute-phase protein made by the liver | How far red cells settle in a tube in one hour, a proxy for fibrinogen and immunoglobulins |
| Speed of change | Rises within 6 hours, peaks at about 48 hours, falls quickly (half-life about 19 hours) | Rises over days and falls over weeks |
| Non-inflammatory influences | Obesity, smoking and pregnancy raise it modestly | Anaemia, pregnancy, age, kidney disease and high immunoglobulins raise it; polycythaemia and sickle cells lower it |
| Typical use | Infection and sepsis, post-operative monitoring, inflammatory bowel disease, point-of-care antibiotic decisions | Giant cell arteritis, polymyalgia rheumatica, myeloma, rheumatoid arthritis monitoring |
| Units and range | mg/L; laboratory upper limit, no diagnostic threshold | mm/h; reference limit rises with age and differs by sex |
| When they disagree | High CRP with normal ESR: early or minor inflammation | High ESR with normal CRP: anaemia, pregnancy, lupus, myeloma or age |
Where CRP test fits
Tracking an acute infection or the response to antibiotics or surgery, where speed matters
Where ESR (erythrocyte sedimentation rate) fits
Suspected giant cell arteritis or polymyalgia, myeloma, and long-term monitoring of some rheumatic diseases
Educational content. A comparison explains what each test, marker or medicine is for and how they differ. It is educational and does not say which one a person should have; that decision belongs to the clinician who knows the person and the question.