Plasma free hemoglobin (PFH) is used to test for hemolysis. PFH is elevated when red blood cells are damaged faster than the hemoglobin can be scavenged. PFH may be elevated in patients on extracorporeal support like extracorporeal membrane oxygenation (ECMO) and patients with ventricular assist devices. Hemolysis occurs in these settings due to increased mechanical shear forces on red blood cells. Some centers consider circuit change for PFH >100, whereas most centers use the number as a trend and look for more gross measures of hemolysis such as hematuria.