GSTM1 and polycythemia: Clinically, post-transplant erythrocytosis (PET), is defined as a perpetual elevation of Hct level of below 51%, a Hb level of a minimum of 16 g/L, or both, when no additional variables are involved.[42] An early study that was carried out at King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia investigated the factors predictive of post-transplant erythrocytosis.