Which serologic measure of inflammation is the most cost-effective and reliable when monitoring inflammatory disease? What should be done if there is a discrepancy in a patient’s C-reactive protein (CRP) level and erythrocyte sedimentation rate (ESR), i.e., high ESR/low CRP or low ESR/high CRP? — Rich Gremillion, MD, Sandy, Utah

Both ESR and CRP can be useful measures of active inflammation, but in many ways, CRP is a more useful test. CRP is made exclusively in the liver and can rise and fall within hours of an acute inflammatory stimulus. In contrast, ESR is more reflective of the concentration of fibrinogen and various noninflammatory immunoglobulins that have half-lives of days to weeks, resulting in a significant lag time in the rise and fall of the ESR. This difference in specificity and rapidity of response often accounts for an apparent discrepancy between the ESR and CRP.

There are conditions in which the ESR remains the more useful test. For example, ESR can be elevated in various paraproteinemias, which often don’t provoke an acute inflammatory response, and in systemic lupus erythematosus and progressive systemic sclerosis. In both conditions, there is typically only a trivial increase in CRP, but the ESR may be very high. The reason for this discrepancy is unclear, but it indicates the two tests are complementary and should be used selectively based on the clinical scenario. — Daniel G. Tobin, MD (158-5)