C-reactive protein and erythrocyte sedimentation rate discordance: frequency and causes in adults.

C-reactive protein (CRP) levels and the erythrocyte sedimentation rate (ESR) are widely used tests of inflammation that sometimes show opposite results. We performed a retrospective cohort study to clarify the frequency and causes of CRP/ESR discordance in adults. Between January and December of 2011, the laboratories of Texas Health Presbyterian Hospital performed 2150 paired CRP/ESR measurements in 1753 patients, 1731 of whom were nonpregnant adults aged ≥ 18 years. Initial CRP and ESR results for each patient were divided into quartiles. CRP/ESR discordance, predefined as results differing by 2 or 3 quartiles, occurred in 212 patients (12%), 105 of whom had high CRP/low ESR discordance (6%) and 107 of whom had high ESR/low CRP discordance (6%). The 212 patients in the CRP/ESR-discordant group (128 women and 84 men) were subdivided into 1 of 6 diagnostic categories, and the causes of discordances were compared. The high CRP/low ESR-discordant group had more patients with infections than the high ESR/low CRP-discordant group (P = 0.001), particularly infections in the urinary tract (P = 0.03), gastrointestinal tract (P = 0.001), lungs (P = 0.005), and bloodstream (P = 0.03). However, they had fewer bone and joint infections than the high ESR/low CRP-discordant group (P = 0.001). Connective tissue diseases, such as systemic lupus erythematosus, were less common in the high CRP/low ESR-discordant group than in the high ESR/low CRP-discordant group (P = 0.001). Ischemic strokes or transient ischemic attacks almost invariably occurred in the high ESR/low CRP-discordant group (P = 0.001), whereas myocardial infarction or venous thromboembolism was limited to the high CRP/low ESR-discordant group (P = 0.001). Our findings provide information to physicians who order these 2 tests together and receive discordant results, which occurs in approximately 1 in 8 patients.