Thrombotic microangiopathies (TMAs) may develop from diverse group of etiologies. While activity levels less than 10% of ADAMTS13 help to clinically diagnose thrombotic thrombocytopenic purpura (TTP), the significance of mild (41%-70%) or moderate (11%-40%) ADAMTS13 deficiency for patients with TMA is unclear. Researchers retrospectively examined 254 TMA patient’s charts from three large medical centers in Boston and compared those patients with mild (N=97) or moderate (N=45) ADAMTS13 deficiency to those with normal activity levels (>70%; N=44). After excluding patients with severe (<10%; N=68) ADAMTS13 deficiency, patients with moderately deficient ADAMTS13 activity tended to be older, more likely to have sepsis (p<0.01), and had a higher international normalized ratio (INR) than patients with no deficiency or mild deficiency (p<0.01). Furthermore, patients with moderately deficient levels had an increased risk of mortality compared to those with mild deficiency. Further research is necessary to determine the best treatment for patients with TMA and moderately deficient ADAMTS13 activity levels as well as the underlying etiologies causing TMA.