We conducted a prospective observational study in the emergency department of a teaching hospital (Bordeaux, France). Patients with minor head injury (2,128) were consecutively included from December 2007 to February 2009. CT scans and plasma S100-B levels were compared for 1,560 patients. The main outcome was to evaluate the diagnostic value of the S100-B test, focusing on the negative predictive value and the negative likelihood ratio.
CT scan revealed intracranial lesions in 111 (7 % ) participants, and their median S100-B protein plasma level was 0.46 ¦Ìg/L (interquartile range [IQR] 0.27 to 0.72) versus 0.22 ¦Ìg/L (IQR 0.14 to 0.36) in the other 1,449 patients. With a cutoff of 0.12 ¦Ìg/L, traumatic brain injuries on CT were identified with a sensitivity of 99.1 % (95 % confidence interval [CI] 95.0 % to 100 % ), a specificity of 19.7 % (95 % CI 17.7 % to 21.9 % ), a negative predictive value of 99.7 % (95 % CI 98.1 % to 100 % ), a positive likelihood ratio of 1.24 (95 % CI 1.20 to 1.28), and a negative likelihood ratio of 0.04 (95 % CI 0.006 to 0.32).
Measurement of plasma S100-B on admission of patients with minor head injury is a promising screening tool that may be of help to support the clinician's decision not to perform CT imaging in certain cases of low-risk head injury.