We had an interesting case in our practice which led to the following two questions. The answers are from UpToDate :
What percentage of children with haematogenous osteomyelitis will have abnormal lab studies?
LABORATORY FINDINGS — Elevations in peripheral white blood cell count (WBC) are variable and nonspecific, while elevations in the erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) are more consistently observed in children with hematogenous osteomyelitis [4,30]. This was illustrated in a review of 44 children with acute hematogenous osteomyelitis in whom serial tests were obtained during therapy .
● The white blood cell count was elevated in only 35 percent.
●The erythrocyte sedimentation rate (ESR) was initially elevated (≥20 mm/h) in 92 percent of patients (mean 45 mm/h).
●The serum C-reactive protein (CRP) concentration was elevated in 98 percent on admission.
How quickly does CRP and the ESR return back to normal in such cases?
ESR and/or CRP levels – The ESR and CRP levels are generally reliable laboratory markers of inflammation and response to therapy. The ESR usually increases during the first several days after diagnosis and then declines in the weeks that follow . CRP also increases early in the infection but returns to normal sooner than ESR. In addition, the rate at which CRP returns to normal may be a sensitive indicator of a complicated clinical course. These observations were demonstrated in the following reports:
•In a prospective series of 50 children treated for acute S. aureus hematogenous osteomyelitis, CRP returned to normal in an average of nine days, compared with 29 days for ESR .
•In a report of 63 consecutive children with hematogenous osteomyelitis, those with a higher CRP from the fourth day of treatment on were more likely to have a complicated clinical course, as defined by requirement for repeated drainage, duration of symptoms, and extent of radiographic findings .
Either ESR or CRP may be used to monitor initial response to therapy, depending on which test is more readily available. Although we prefer monitoring both levels, CRP begins to decline sooner.