The estimated prevalence of inappropriate AST is unknown. Assuming a worst case scenario of 50 % inappropriate AST, 384 patients would need to be included in the trial for a confidence interval of 95% (see table below). Assuming a rate of 30 % of inappropriate AST, 323 patients would need to be included. To guarantee this sample size at least 500 medical files will be screened in order to compensate for potential dropouts. These 500 medical files will be randomly selected out of all the included patients using a random code generator. In UZ Leuven at least 500 medical records will be screened, supplementary other participating hospitals are requested to screen 20 medical files each.