According to the authors, since the primary source of bilirubin is the degradation of hemoglobin (Hb) in plasma by macrophages from the reticuloendothelial system, it can serve as a diagnostic marker for Gilbert’s syndrome (GS), as an increase in its blood concentration follows an increase in bilirubin levels (≥6 μmol/L). The gene discussed is GSTM1; the disease is Gilbert syndrome.