GSTM1 and anemia (phenotype): At the multivariate level of analysis, the presence of anemia (Hb < 8) (aRR = 1.376, CI = 1.159–1.634, P =  < 0.001) and having a perforated appendix (aRR = 1.263, CI = 1.026–1.555, P = 0.027) were independently associated with the occurrence of complications.