Erythrocyte sedimentation rate and C-reactive protein: how best to use them in clinical practice.

Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are markers of inflammatory conditions and have been used extensively by clinicians both in outpatient and inpatient settings. It is important to understand the physiologic principles behind these two tests so clinicians may use them appropriately. For example, fibrinogen (for which ESR is an indirect measure) has a much longer half-life than CRP, making ESR helpful in monitoring chronic inflammatory conditions, whereas CRP is more useful in diagnosis as well as in monitoring responses to therapy in acute inflammatory conditions, such as acute infections. Many factors can result in falsely high or low ESR and CRP levels, and it is important to take note of these. Therefore, if used wisely, ESR and CRP can be complementary to good history taking and physical examination in the diagnosis and monitoring of inflammatory conditions.