CRP and rheumatoid arthritis: CRP levels were generally within normal range (< 5 mg/L [30]; 0.26–14.30 mg/L) throughout the first 7 days in the study (Fig. 2), with active inflammation (≥ 5 mg/L) observed in 22 of 234 samples (9.4%; 8 participants 4 RA, 2 OA, 2 FM).