Clinical features and outcomes in patients with thrombotic microangiopathy not associated with severe ADAMTS13 deficiency.

BACKGROUND

The a disintegrin and metalloprotease with thrombospondin type 1 motifs, member 13 (ADAMTS13) activity assay has become important in distinguishing autoimmune thrombotic thrombocytopenic purpura from other forms of thrombotic microangiopathy (TMA). Although the significance of severe deficiency in ADAMTS13 (activity levels 10% or less) has been well defined, little data are available on the clinical importance of mild to moderate deficiency (activity levels 11%-70%) among patients with TMA.

STUDY DESIGN AND METHODS

We conducted a retrospective study using the Harvard TMA Research Collaborative Registry. Among 254 patients who met the inclusion criteria for TMA, 186 patients with ADAMTS13 activity levels greater than 10% were divided into moderate-deficiency (11%-40%), mild-deficiency (41%-70%), and no-deficiency (greater than 70%).

RESULTS

Compared with mild or no deficiency, moderate ADAMTS13 deficiency correlated with older age; higher bilirubin and international normalized ratio; and increased frequency of sepsis, shock, or multiorgan failure. Platelet counts, lactate dehydrogenase levels, and the presence of renal or neurologic dysfunction did not vary across the three patient cohorts. While moderate ADAMTS13 deficiency was associated with increased 90-day mortality in univariate analysis, this association was no longer significant in multivariate analysis. Variables that independetly predicted 90-day mortality in this cohort of patients included Charlson comorbidity index, alanine aminotransferase level, platelet count, creatinine, and the presence of sepsis, shock, or multiorgan failure.

CONCLUSION

Moderately deficient ADAMTS13 activity identifies a cohort of patients with TMA who are at increased risk for 90-day mortality. The ADAMTS13 activity level in this group is not an independent predictor of poor outcomes but instead appears to be a marker of disease acuity.