Microangiopathic haemolytic anaemia (MAHA) describes non-immune haemolysis by intravascular fragmentation of red blood cells, resulting from microvascular thrombosis characteristic of thrombotic microangiopathy (TMA). TMA-associated MAHAs include several diseases but are mostly associated with thrombotic thrombocytopenic purpura (TTP) and haemolytic-uremic syndrome (HUS). TTP is caused by a severe deficiency in ADAMTS13 proteinase, responsible for regulating coagulation, either due to presence of anti-ADAMTS13 (acquired iTTP; immune-mediated) or mutations in ADAMTS13 itself (congenital cTTP). HUS is caused by abnormal and uncontrolled complement activation, either by bacterial toxin activity (typical dHUS) or lack of normal regulatory proteins (atypical aHUS). This review focuses on TTP and HUS in relation to MAHA aetiology, pathogenesis, diagnosis and treatment.

The overlap in clinical presentation between TTP and HUS emphasise the importance of specific diagnostic assays in differential diagnosis. Therapeutic plasma exchange (TPE) and renal replacement therapy (RRT) are reported as relatively effective standard treatment methods. However, novel therapies for TTP (Caplacizumab) and HUS (complement blockade therapy or Eculizumab) currently undergoing clinical trials should be reviewed for future use once approved and validated, to further improve patient prognosis, as both TTP and HUS mortality rates remain significantly high (5-16% and 15-33% respectively).