Evaluation of a bedside immunotest to predict individual anti-tetanus seroprotection: a prospective concordance study of 1018 adults in an emergency department

Background: Unscheduled tetanus prophylaxis (UTP) used in the emergency room (ER) in patients with wounds who are unaware of their vaccination history is erroneous in 40% of cases. Evaluation of bedside tetanus immunity with the Tetanos Quick Stick (TQS) test may improve UTP. Objectives: To show that (1) a positive TQS result reflects immunity to tetanus; and (2) TQS is reproducible by ER workers. Methods: In a prospective concordance study, immunity to tetanus of patients with wounds was assessed by two techniques: (1) TQS at the bedside, which detects specific tetanus antitoxins at concentrations >= 0.2 IU/ml in whole blood or >= 0.1 IU/ml in serum; (2) ELISA in the laboratory (threshold >0.1 IU/ml). The study comprised three groups: (A) healthcare personnel self-tested with the two techniques to determine the effect of training; (B) selected patients with wounds were double-tested with TQS by two healthcare providers whose readings were compared to test reproducibility; and (C) all patients with wounds aged >= 15 years were consecutively included. Results: Of 1018 individuals included, 60 were in group A, 50 were in group B and 908 were in group C. 403 patients who were not included were similar to those included for age, vaccination history and types of wounds. The reproducibility of the test was 98%. TQS sensitivity was 83.0%, specificity 97.5%, positive predictive value 99.6% and negative predictive value 42.9%. Conclusions: TQS reliably predicts tetanus immunity and is reproducible by healthcare providers. Although it may not accurately discriminate between patients with ongoing and declining immunity, it is currently the most sensitive and specific tool for guiding tetanus prophylaxis and should be included in current guidelines on UTP.