Usefulness of determining serum S-100â protein expression in screening patients with minor head injury in a hospital emergency department

Objectives: To validate testing for S-100â protein expression in minor head injury in

comparison with computed tomography (CT) brain scans as the gold standard. To

evaluate the role this screening approach might play in a hospital emergency

department and set a cutoff point that could identify patients without CT evidence of

brain injury.

Methods: Data for 100 patients over the age of 14 years who came to the emergency

department with minor head injury were included. Some patients had additional

symptoms. All agreed to participate in the study. Serum S-100â levels were determined

and a CT scan performed in all enrolled patients. The findings, as well as symptoms and

the findings of physical examination, were recorded. Statistical analysis included the

study of sensitivity, specificity, predictive values, likelihood ratios, contingency tables,

and the area under the receiver operating characteristic curve.

Results: CT scans were normal in patients with a serum S-100â level below 0.1375 ìg/L.

Concentrations below that cutoff were found in 44% of the sample. CT scans were

positive in 7% and these patients (mean age, 42 years) all had S-100â levels above the

cutoff. The sensitivity of the test was 100%; specificity was 47%. The negative predictive

value was 100%, but the positive predictive value was 12%. The overall predictive value

was 51%. The positive and negative likelihood ratios were 1.9 and 0, respectively. The

area under the receiver operating characteristic curve of S-100â levels was 0.653.

Conclusions: Early determination of S-100â blood levels could reduce the number of CT

scans required for patients with minor head injury by nearly half. The number of patients

admitted to the observation unit could also be reduced.