Procalcitonin Is a Specific Marker for Detecting Bacterial Infection in Patients with Rheumatoid Arthritis

Sato H et al. – Serum procalcitonin (PCT) level is a more specific marker for detection of bacterial infection than either CRP, ESR, or WBC count in patients with Rheumatoid arthritis (RA). High PCT levels (≥ 0.5 ng/ml) strongly suggest bacterial infection. However, PCT < 0.5 ng/ml, even if < 0.2 ng/ml, does not rule out bacterial infection and physicians should treat appropriately.

Methods

• One hundred eighteen patients experiencing an RA flare, noninfectious complication of RA or its treatment, nonbacterial infection, or bacterial infection were studied.
• Serum PCT concentrations were determined with a chemiluminescent enzyme immunoassay.

Results

• All patients experiencing an RA flare showed negative PCT levels (≤ 0.1 ng/ml; n = 18).
• The PCT level was higher in the bacterial infection group (25.8% had levels ≥ 0.5 ng/ml) than in the other 3 groups (0.0–4.3% had levels ≥ 0.5 ng/ml) and the difference was significant among groups (p = 0.003).
• Conversely, no statistically significant difference was observed among the groups with C–reactive protein (CRP) concentration ≥ 0.3 mg/dl (p = 0.513), white blood cell (WBC) count > 8500/mm3 (p = 0.053), or erythrocyte sedimentation rate (ESR) > 15 mm/h (p = 0.328).
• The OR of high PCT level (≥ 0.5 ng/ml) for detection of bacterial infection was 19.13 (95% CI 2.44–149.78, p = 0.005).
• Specificity and positive likelihood ratio of PCT ≥ 0.5 ng/ml were highest (98.2% and 14.33, respectively) for detection of bacterial infection, although the sensitivity was low (25.8%).

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