Objective: The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are laboratory tests that have been said to have a strong correlation with a positive temporal artery biopsy in patients with suspected giant cell arteritis (GCA). Published reports suggest that the CRP is a more sensitive diagnostic indicator of GCA and can be elevated when the ESR is normal. It is also clear that the CRP and ESR can both be normal or both be elevated in patients with biopsy-proven GCA and that the CRP can be elevated when the ESR is normal. The purpose of this study was to ascertain if the CRP can be normal when the ESR is elevated in biopsy-proven GCA. Design: Retrospective, longitudinal, comparative study. Participants: One hundred nineteen patients from 6 major tertiary-care university-affiliated medical centers. Methods: The charts from 119 patients with temporal artery biopsies positive for GCA were reviewed for age, gender, pretreatment ESR, and pretreatment CRP. Main Outcome Measures: The ESR in millimeters per hour Westergren was graded as normal or abnormal based on 2 validated formulas. The CRP was graded as normal or abnormal based on established criteria set forth in the literature as well as at The Johns Hopkins Hematology laboratory. Results: In this study, the ESR had a sensitivity of 76% to 86%, depending on which of 2 formulas were used, whereas an elevated CRP had a sensitivity of 97.5%. The sensitivity of the ESR and CRP together was 99%. Only 1 of the 119 patients (0.8%) presented with a normal ESR and normal CRP (double false negative); 2 patients (1.7%) had a normal CRP despite an elevated ESR according to both formulas. Conclusion: Although most patients with GCA have both an elevated ESR and CRP, there can be nonconcordance of the 2 blood tests. Although such nonconcordance is most often a normal ESR but an elevated CRP, the finding of an elevated ESR and a normal CRP also is consistent with GCA. The use of both tests provides a slightly greater sensitivity for the diagnosis of GCA than the use of either test alone.
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