A comparison of two different assays for determining S-100B in serum and urine

Background: Brain injury after head trauma can be detected by S-100B measurements in serum. Recent preliminary studies indicate that urinary levels of S-100B are also increased after head injury, a finding that is of possible clinical value. The aims of the present study are two-fold: to compare serum measurements of two assays, the Liaison Sangtec (R) 100 system and the Elecsys (R) S100 test, and to investigate to what extent they can detect and measure S-100B in urine. Methods: A total of 191 serum and 174 urine samples from 107 patients (children aged between 1 and 18 years following head trauma) were measured with both assays. The results were compared using correlation analysis and Bland-Altman difference plots. Results: Serum values of the Sangtec (R) system ranged from 0.02 to 2.28 mu g/L, and from 0.005 to 2.13 mu g/L for the Elecsys (R) test. Comparisons showed a clear correlation (correlation coefficient 0.80) but not an agreement between the methods. The Sangtec (R) system could only detect S-100B in 20 out of 174 urine samples (range 0.02-0.06 mu g/L), whereas the Elecsys (R) test could detect S-100B in 171 samples (range 0.005-0.14 mu g/L). No clear relation was observed between the two methods in urine analysis (correlation coefficient 0.60). Conclusion: The Sangtec (R) and Elecsys (R) assays are not interchangeable methods when analyzing S-100B in serum or urine samples after head injury.