The erythrocyte sedimentation rate (ESR), the measurement of erythrocyte settling rate in anticoagulated blood under standard conditions, is a common clinical laboratory test which is a nonspecific indicator of infection and tissue injury.^1,2 In contrast to the ZSR (Zeta Sedimentation Ratio), the ESR is greatly influenced by packed cell volume.³ ESR and viscosity are preferred for monitoring chronic inflammation, including disease severity in rheumatoid arthritis.³ ESR and C-reactive protein measurements are the assays used most often by rheumatologists in monitoring response to treatment in inflammatory diseases, such as rheumatoid arthritis (RA).⁴ Fibrinogen and alpha₁-acid glycoprotein are also useful for detection of chronic inflammatory disease. Combined use of ESR and C-reactive protein (CRP) concentrations are useful in assessing the severity of acute pelvic inflammatory disease.⁵ The ESR is more useful than serum CRP for diagnosis and monitoring of polymyalgia rheumatica/giant cell arteritis (PMR/GCA) and is more frequently elevated during relapse. Normal values for ESR or CRP do not exclude a diagnosis of either PMR or GCA, nor do normal values exclude relapse.⁶ Measurement of more specific acute phase reactants (e.g., CRP, C4, haptoglobin, and (1-antitrypsin) is not more helpful diagnostically than the ESR,⁷ which by itself is not useful for excluding underlying infection or inflammation with a certainty of 95%.⁸ Men aged 45-64 with ESR in the upper quintile have more than twice the risk of coronary heart disease death of men with ESR in the lowest quintile after adjusting other risk factors.⁹