GPT and substance abuse: Compared to the risk-based phase, patients identified during the birth-cohort phase were significantly less likely to have a documented history of substance abuse (30.5 % vs. 49.5 %, p = 0.02), an ALT measurement > 40 U/L (22.0 % vs. 46.7 %, p = 0.002), or the composite any risk-associated factor (55.9 % vs. 79.0 %, p = 0.002).