A study of 589 total elbow arthroplasty patients, using the ACS-NSQIP database, discovered that anemia was a significant predictor of prolonged LOS, with the proportion of patients with prolonged LOS increasing significantly with increasing levels of anemia.[39] In another case-control study involving 1259 patients with hip fractures,[40] Cao H et al reported that Hb was a significant predictor of prolonged LOS (OR = 1.920, 95% CI: 1.045 to 3.529, P = .036). The gene discussed is GSTM1; the disease is anemia (phenotype).