PA14.1-2 | Microcytic Anaemia Differentials: Thalassaemia, ACD, Sideroblastic — Summary & Reflection

REFLECT

Synthesis prompt — take 5 minutes before reading on:

You are posted in the clinical pathology (CP) department. Three blood samples arrive from the outpatient haematology clinic, each with a request for 'microcytic anaemia work-up'. You have CBC, reticulocyte count, ferritin, and transferrin saturation for each. HPLC and bone marrow are available but take time and cost resources.

Sample 1: Hb 8.2, MCV 74, RBC 3.9M, RDW 19%, Ferritin 5, Transferrin sat 8%. Reticulocytes: 0.8%.

Sample 2: Hb 10.5, MCV 65, RBC 5.7M, RDW 12.8%, Ferritin 95, Transferrin sat 28%. Reticulocytes: 1.6%. Patient note: 'Sindhi, asymptomatic, routine check'.

Sample 3: Hb 9.0, MCV 78, RBC 4.1M, RDW 18%, Ferritin 310, Transferrin sat 72%. Reticulocytes: 1.1%. Patient note: 'Chronic alcoholic, referred from medicine'.

Before requesting HPLC or bone marrow:
1. What is your working diagnosis for each sample?
2. Which sample needs HPLC? Which needs a bone marrow?
3. Which sample should NOT receive iron therapy?

Write your answers before reading the summary block.

KEY TAKEAWAYS

Reflection answers + SDL summary:

Sample 1 → Classic IDA: Ferritin 5 (depleted), high RDW (anisocytosis), low RBC, low transferrin sat. Treat with oral iron. No HPLC needed.

Sample 2 → Beta-thalassaemia trait: Mentzer = 65/5.7 = 11.4 (<13), isocytosis (RDW 12.8%), high RBC, normal ferritin. Sindhi ethnicity confirms suspicion. Order HPLC — expect HbA2 >3.5%. Do NOT give iron. Refer for genetic counselling + premarital partner screening.

Sample 3 → Sideroblastic anaemia (alcohol-induced): Very high ferritin 310 + very high transferrin saturation 72% (iron overload paradox) + high RDW (dimorphic picture likely) + alcohol history. Order bone marrow Perls stain for ringed sideroblasts. Recommend alcohol cessation. B6 trial. Iron chelation if confirmed overload.

Core take-aways from this SDL:

1. TAILS mnemonic covers the five causes of microcytosis: Thalassaemia, ACD, IDA, Lead, Sideroblastic. In India, your working differential is almost always IDA vs thalassaemia trait vs ACD.

1. The CBC alone cannot diagnose microcytic anaemia. Iron studies (ferritin, TIBC, transferrin saturation) are the first essential step.

1. The Mentzer Index (MCV ÷ RBC) provides a rapid initial screen: <13 → thalassaemia trait; >13 → IDA. Confirm with HPLC.

1. The TIBC discriminates IDA from ACD: IDA → HIGH TIBC. ACD → LOW TIBC. Both have low transferrin saturation, but the ferritin is opposite: IDA = low ferritin; ACD = high/normal ferritin.

1. Sideroblastic anaemia paradox: HIGH ferritin + HIGH transferrin saturation + ANAEMIA. Iron is present in excess but cannot be used. Dimorphic smear is the clue; Perls marrow is the proof.

1. Iron supplementation is wrong in thalassaemia trait (iron stores are normal to high) and in pure ACD (stores are adequate; hepcidin blocks iron use). Giving iron to the wrong patient causes iatrogenic iron overload.

1. Indian context: Beta-thal trait prevalence 3-4% nationally, up to 15% in some communities. Any asymptomatic patient with disproportionate microcytosis and low Mentzer index from a high-risk community deserves HPLC before any other intervention.

Forward link: SDL4 (H3-SDL4) will put peripheral blood smears on screen and ask you to identify these patterns in real images — thalassaemia target cells, sideroblastic dimorphic picture, IDA pencil cells. For the deeper molecular genetics of thalassaemia (alpha vs beta gene deletions, HbH disease, haemoglobin Bart's, sickle-thal compound), see H5-SDL2 (haemolytic anaemias).