Practical approach to the differential diagnosis of TMA. The initial differential diagnosis of a TMA focuses on differentiating TTP from aHUS, also termed primary complement-mediated TMA, from the multiple causes of secondary TMA since this will impact initial treatment. There is evidence the complement acts as a driver for some secondary TMAs (with and without complement mutations), and complement inhibition may be a useful therapeutic strategy if control of the underlying disorder does not lead to improvement in the TMA and renal function. CM-TMA, complement-mediated TMA.