It is a 7-tier system used to categorize TMA patients according to their risk of severe ADAMTS13 deficiency, based on platelet count (<30 × 109/L), hemolysis (indirect bilirubin >2 mg/dL or reticulocyte count >2.5% or undetectable haptoglobin), active cancer, previous transplantation, mean corpuscular volume (MCV) <90 fL, international normalized ration (INR) <1.5, and creatinine < 2.0 mg/dL [38,42]. Here, HP is linked to cancer.