BACKGROUND A pilot study was designed to determine if serum procalcitonin levels would assist in the diagnosis of severe bacterial infections in patients presenting to an emergency department (ED) with acute sickle cell pain crisis and evidence of acute inflammatory response. METHODS Prospective single cohort study evaluating measured procalcitonin levels in patients with sickle cell pain crisis and evidence of acute inflammation. Acute inflammation was defined as fever (>38 degrees C) and/or elevation in the white blood cell count (>4000 above baseline) and tachycardia (heart rate >100). Procalcitonin was measured using a semi-quantitative monoclonal antibody test. Patients were followed clinically to determine if procalcitonin has predictive value in excluding severe bacterial infections. RESULTS Twenty four subjects were enrolled and completed the study. Sixteen had levels 0.5 ng/ml or less, two had levels 0.5 to 2 ng/ml, one had a level of 2 but less than 10 ng/ml, and four had levels 10 ng/ml or greater. All subjects with documented infections at presentation had procalcitonin levels > or =2.0 ng/ml. The sensitivity of the test in this study sample was 1, and the specificity was 0.95 (95% CI, 0.75-0.99). CONCLUSIONS A serum procalcitonin less than 2 ng/ml appears to have good negative predictive value in excluding serious bacterial infections in patients that present with acute sickle cell pain crisis and evidence of acute inflammatory response. Further study is needed to investigate if procalcitonin has positive predictive value in identifying patients with serious bacterial infections in this patient population.