What is the utility of CRP in guiding treatment response in osteomyelitis?

The Bottom Line: Traditionally erythrocyte sedimentation rate and leukocyte cell count have been used, whereas C-reactive protein has gained in popularity. The study monitored 265 children at ages 3 months to 15 years with culture-positive osteoarticular infections with a predetermined series of ESR, CRP, and leukocyte count measurements. On admission, ESR exceeded 20 mm/hour in 94% and CRP exceeded 20 mg/L in 95% of the cases, the mean (± standard error of the mean) being 51 ± 2 mm/hour and 87 ± 4 mg/L, respectively. ESR normalized in 24 days and CRP in 10 days. Elevated CRP gave a slightly better sensitivity in diagnostics than ESR, but best sensitivity was gained with the combined use of ESR and CRP (98%). Elevated ESR or CRP was seen in all cases during the first 3 days. Measuring ESR and CRP on admission can help the clinician rule out an acute osteoarticular infection. CRP normalizes faster than ESR, providing a clear advantage in monitoring recovery.

Paakkonen, Markus, et al. “Sensitivity of erythrocyte sedimentation rate and C-reactive protein in childhood bone and joint infections.” Clinical orthopaedics and related research 468.3 (2010):861-866.

Acute osteoarticular infections of childhood comprise essentially three entities, septic arthritis (SA), osteomyelitis (OM), and their combination (OM + SA). Historically these were diseases of high mortality.
ESR is still the main yardstick in monitoring the course of illness [1, 5, 24, 31]. Unfortunately, ESR increases rather arbitrarily and normalizes so slowly that active infection is likely to have resolved earlier than suggested by normalized ESR values
Serum CRP challenges the traditional position of ESR for diagnostics and followup of invasive bacterial infections such as osteoarticular infections of childhood. Three reasons justify its active use. First, in the appropriate context, increased serum concentrations provide a good hint toward an invasive bacterial infection. Second, the increases and decreases of CRP are so clear cut and fast (increased values are seen within 6 to 8 hours, and the doubling time is only 8 hours) that they have the potential to influence treatment. Furthermore, if the infection subsides, the levels decline by approximately 50% a day. Third, as the CRP alternations may be hundreds-fold, quantitative measurements are easy, quick (in 5 minutes if needed), and inexpensive.

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