GSTM1 and acute kidney injury: Much evidence supports a role of heme toxicity in ischemic AKI.4,45,48,50,52,53 In fact, transient heme in the urine is such a prominent feature of ischemic AKI following shock in humans54 that the syndrome was once referred to as “hemoglobinuric nephrosis.”4,45,55 The source of these hemeproteins, however, has remained a mystery for over 70 yr.45,56 We hypothesized that extravasation of Hb or other blood proteins out of the RBC-congested OM capillaries may be the primary source of heme in AKI.