Select where VISITNUM = 1 (or screening visit). Compute from HEIGHT and WEIGHT, using the Du Bois method. BSA = 0.007184 × W0.425 × H0.725
There are multiple methods for calculating BSA (e.g., Du Bois, Mosteller, Haycock, Gehan & George, Boyd, Fujimoto, Takahira, Schlich); the study protocol should describe which to use.