The serum amyloid A to C-reactive protein ratio is lower in men than in women because of higher-C-reactive protein concentrations in men.

Objectives: We previously found that discrepancy between serum amyloid A (SAA) and C-reactive protein (CRP) levels linked to the difference of SAA/CRP ratio in patients with early rheumatoid arthritis, and the ratio varied among different patients. This study aimed to determine why the SAA/CRP ratio differed among different patients.

Methods: The patients (n=466) with most of inflammatory diseases were enrolled. After examined CRP and SAA concentrations, we compared the SAA/CRP ratio, and SAA and CRP concentrations in men and women.

Results: The SAA/CRP ratio varied dramatically among different patients (33.6-0.140). The 10 highest SAA/CRP ratios were all in women, and half of the 10 lowest ratios were found in men. The loge SAA/CRP ratio was significantly higher in women than in men (p<0.0001). The loge SAA concentration was not different between women and men (p=0.174), but the loge CRP concentration was significantly higher in men (p<0.0001).

Conclusions: The SAA/CRP ratio varies considerably among different patients. The SAA/CRP ratio in women is higher than in men because loge CRP but not SAA concentrations in men are higher than in women. The finding is against the conventional view and suggest the reference range of CRP concentration in women should be assessed lower than in men.