24th May 2023

Microangiopathic haemolytic anaemia (MAHA)

Disseminated Intravascular Coagulation (DIC)

DIC is a high mortality, hypercoagulable state due to activation of the coagulation cascade, fibrin and platelet thrombi formation in small vessels, and RBC shearing on fibrin strands. DIC is precipitated by sepsis, trauma, malignancy, and obstetric haemorrhage. It is a consumptive state where bleeding occurs when clotting factors and platelets are used up as part of the hypercoagulable process.

Laboratory findings – thrombocytopenia, prolonged partial prothrombin time and prothrombin time, raised D-dimer, low fibrinogen

Treatment – treat underlying cause e.g. antibiotics in sepsis, heparin for thrombotic predominant patients, replenishment of clotting factors (using fresh frozen plasma) and platelets in patients with a bleeding source or who require interventions with a high bleeding risk

Thrombotic Thrombocytopenic Purpura (TTP)

TTP is another MAHA associated with significant morbidity and mortality. It is due to either an inherited defect or acquired antibody to the ADAMTS13 enzyme which cleaves large von Willebrand Factor (vWF) multimers. Without effective action of the ADAMTS13 enzyme, these large vWF multimers cause platelet aggregation and thrombi formation in small blood vessels. This process results in mechanical RBC fragmentation and thrombocytopenia.

Clinical presentation – Purpura, neurological disturbance (e.g. TIA/stroke, seizures, focal neurology), acute kidney injury (not as severe as HUS), fever

Laboratory bloods – Low platelets, normal coagulation, normal white cell count, raised LDH and bilirubin

Blood film – Schistocytes

Schistocytes on a blood film.

Image Source: Wikimedia Commons (2013). Blood smear with typical schistocytes in TTP marked in blue, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Blood_smear_with_typical_schistocytes_in_TTP_marked_in_blue_1.tif (Accessed on: 10 January 2023).

Management – Plasma exchange (within 24 hours of presentation), corticosteroids and rituximab

Haemolytic Uremic Syndrome (HUS)

Acute infection by Shiga toxin producing bacteria (namely E. Coli O157:H7) characterised by the triad of thrombocytopenia, acute kidney injury and microangiopathic haemolytic anaemia. HUS usually occurs in children but can present in adults.

Clinical features – nausea and vomiting, bloody diarrhoea, haematuria, weakness, abdominal pain

Laboratory bloods – Anaemia, thrombocytopenia, AKI (raised urea, creatinine, low eGFR), raised reticulocytes, raised LDH, raised bilirubin, low haptoglobin, negative DAT, normal PT and PTT, proteinuria

Bloods film – Schistocytes

Management – Supportive (intravenous fluid administration). Avoid use of antibiotics as it can worsen HUS (unless septic).