The diagnostic and prognostic value of admission serum levels of interleukin-6 (IL-6) and C-reactive protein (CRP) was investigated in 203 hospital-treated patients with community-acquired pneumonia (CAP). In serum samples obtained during the first 24 h after admission, IL-6 was detectable in 198 patients (98%), with a median value of 50 ng/l. Ten % of the patients had IL-6 values of 1000 ng/l. A clear positive correlation between IL-6 and CRP was found (r = 0.29, p < 0.0001). Patients with high IL-6 or CRP levels had longer duration of fever, longer hospital stay, and had less often recovered clinically or radiographically on follow-up weeks after discharge. A high IL-6, but not a high CRP, also seemed to be associated with a higher mortality. Bacteremic pneumococcal pneumonia had the highest levels of IL-6 (mean 2852 and median 420 ng/l) and CRP (mean 292 and median 285 mg/l). High IL-6 values were also seen in patients with non-bacteremic pneumococcal pneumonia, while all patients with pneumonia due to other bacterial, or viral, aetiology had IL-6 levels of < or = 300 ng/l. In conclusion, IL-6 and CRP are promising diagnostic and prognostic tools in the management of CAP. Further studies are needed to establish the usefulness of repeated measurements early in the hospital course of the disease.

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Repeated laboratory tests for CRP and WBC should be performed in patients with suspected acute appendicitis requested to stay for further observation. If these test results are normal, the surgeon should preferably refrain from operating but consider other differential diagnoses.