Comparison of sample materials for S100b analysis.

Head injury is a potentially lethal and frequently occurring condition in the emergency department (ED). Reliable and fast diagnosis is important both for patients and flow in the ED. Circulating S100B is used to rule out the need for head computer tomography in low-risk patients with mild head injury. The flow of these patients through the ED would benefit from shorter turn-around time. Standard serum clotting tubes require 30-60 min clotting time, followed by an analysis time of 45 min. Here, we evaluated the performance of two alternative blood collection tubes; a rapid serum tube (RST) with a recommend clotting time of 5 min and a hirudin tube (HIR) for instant anticoagulation. S100B measurement was performed on paired blood samples from 221 subjects using a Roche Cobas 602 analyser. The performances of the alternative tubes were evaluated by method comparison to the standard serum clotting tube, repeatability and agreement of results obtained from alternative tubes compared with the standard clotting tube. Both alternative tubes had a minor positive bias (RST = 0.011 µg/L, HIR = 0.008 µg/L). The repeatability was 2% for RST and 10% for HIR, while being 4% for the standard clotting tube. In the agreement analysis, the positive and negative predictive values for RST were 62% and 100% while being 73% and 99% for HIR respectively. Our study suggests that RST is a feasible alternative to reduce laboratory turn-around time in S100b analysis.