CRP (C-reactive protein) / ESR (erythrocyte sedimentation rate)
Erythrocyte sedimentation rate or sedrate (ESR) and C-reactive protein (CRP) are commonly ordered tests for arthritis. During the acute phase response to a local or systemic inflammatory process, plasma proteins dramatically increase. C-reactive protein is one of the major plasma proteins generated, and is easily measured by laboratory testing.
Measures of Inflammation
In general both ESR and CRP measure the increase in inflammatory generated proteins.
- CRP is a direct measurement of C-reactive protein.
- ESR indirectly measures many proteins associated with inflammation.
There are subtle differences in the behavior of the tests, depending on the suspected disease.
Are the Tests Disease-Specific? Are CRP and ESR Elevated in All Inflammatory Conditions?
The answer is no to both questions.
In rheumatoid arthritis which is a known inflammatory type of arthritis, there are cases where both the ESR and CRP are normal, particularly during the earliest stages of the disease. In certain patients, the reason for this appears to be an insensitivity or low level of a triggering mechanism that normally stimulates the liver to produce the inflammatory proteins necessary for ESR and CRP testing.
The diagnosis of rheumatoid arthritis, therefore, is not dependent on the presence of either test.
- Do normal blood test results rule out rheumatic disease?
- What blood tests are commonly ordered to diagnose and monitor arthritis?
- Do blood tests monitor the effectiveness and toxicity of arthritis treatments?
Answer provided by rheumatologist Raymond Federman, M.D.