PA16.1-3 | Acquired Haemolytic Anaemias & Smear Morphology — Summary & Reflection

REFLECT

Before checking the summary, take 60 seconds:
1. A 45-year-old woman with SLE develops sudden severe anaemia. Smear shows spherocytes. You run a DAT — it returns positive for IgG and C3d. Which type of AIHA is this? What is your first-line treatment?
2. A patient post-cardiac valve replacement has mild persistent anaemia with schistocytes but normal platelets. Is this TTP? What single test is most helpful?
3. A child with bloody diarrhoea caused by E. coli O157:H7 develops oliguria and haemolytic anaemia. What morphology do you expect on smear? Why is the DAT negative?

KEY TAKEAWAYS

Acquired haemolytic anaemias — the essentials:

• Warm AIHA — IgG, extravascular (splenic), spherocytes, DAT IgG-positive; causes: lymphoma, SLE, drugs.
• Cold AIHA — IgM, complement-mediated, predominantly hepatic; RBC agglutination on smear; DAT C3d-positive only; causes: Mycoplasma, EBV.
• DAT — gold standard for immune vs. non-immune split; IgG = warm, C3d only = cold, negative = MAHA/PNH/mechanical.
• MAHA — mechanical fragmentation; schistocytes; DAT negative; TTP (ADAMTS13↓, pentad), HUS (Shiga toxin, renal-dominant), DIC (coagulopathy + MAHA).
• PNH — somatic PIG-A mutation; absent CD55/CD59; complement-mediated intravascular lysis; diagnosed by flow cytometry; venous thrombosis is a key complication.
• Smear morphology is the first diagnostic move: spherocytes → immune, schistocytes → MAHA, bite cells → oxidative, agglutination → cold AIHA.
• Lab triad of haemolysis: ↑LDH + ↑indirect bilirubin + ↓haptoglobin, ± reticulocytosis.