C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are both nonspecific markers of infllammation somewhere in the body.   Most of the time, the ESR does not change as rapidly as does the CRP, either at the start of inflammation, or as it goes away.  Because the CRP is not affected by as many factors as is the ESR, it is usually considered to be a more reliable marker of inflammation. (But, the ESR is cheaper and quicker to perform, so many doctors still use the ESR first, when they suspect that a patient has inflammation.) Menstruation and pregnancy can cause slight, temporary elevations and flucuations of both ESR and CRP levels. As a matter of fact, the low normal ESR level for females is higher than is the low normal level for males.