IM9.6-9 | Anaemia Diagnostic Testing — Summary & Reflection

KEY TAKEAWAYS

Anaemia diagnostic testing follows a tiered, hypothesis-driven approach anchored in clinical pre-test probability:

First tier: CBC + red cell indices + peripheral smear. MCV classifies morphologically (microcytic/normocytic/macrocytic); reticulocyte count classifies kinetically (hypo- vs hyperproliferative). RDW distinguishes IDA (elevated, early) from thalassaemia trait (normal) in microcytic anaemia.

Second tier (targeted by morphological class):
- Microcytic: Iron studies panel — ferritin (best single test; acute-phase reactant caveat), serum iron, TIBC, TSAT. Pattern: IDA = low ferritin + high TIBC + low TSAT; ACD = normal/high ferritin + low TIBC + low TSAT; thalassaemia trait = normal ferritin + normal TIBC + normal/high TSAT.
- Macrocytic: B12 + folate levels; MMA (B12-specific) + homocysteine (both B12 and folate); anti-intrinsic factor antibody (pernicious anaemia).
- Haemolytic: LDH + unconjugated bilirubin + haptoglobin (undetectable = intravascular haemolysis) + reticulocyte count; DAT (positive = AIHA; negative = non-immune haemolysis).

Third tier (aetiological): GI endoscopy (IDA in adults >40 or any adult male/post-menopausal female), haemoglobin electrophoresis (thalassaemia, SCD), G6PD assay (enzyme-deficiency haemolysis), BMA (aplastic anaemia, MDS, haematological malignancy, unexplained pancytopaenia, sideroblastic anaemia).

Key India-relevant points: Thalassaemia trait is common in Gujarat and Maharashtra (confirm with HbA2 >3.5% on electrophoresis); sickle cell disease is prevalent in tribal populations in Odisha, Chhattisgarh, and central India; G6PD deficiency is common across the subcontinent; metformin causes B12 deficiency in long-term users; IDA in adult males and post-menopausal women always requires GI source investigation.

REFLECT

Reflect on the central theme of this module: diagnostic tests in anaemia are not independent data points but pieces of a physiologically integrated picture. The ferritin, the TIBC, the TSAT, the smear morphology, and the reticulocyte count each illuminate a different compartment of the red cell lifecycle — storage, transport, erythropoietic utilisation, morphological integrity, and marrow response. A clinician who understands this integration can arrive at the correct diagnosis efficiently; one who orders panels without interpreting them as a pattern will misdiagnose consistently. Think about a patient with microcytic anaemia you might encounter in a rural health setting where haemoglobin electrophoresis is not immediately available. Which combination of the simpler tests — Mentzer index, RDW, iron studies — would you use to most confidently distinguish IDA from thalassaemia trait, and how would that triage decision change your immediate management? How would you explain to the patient why you are not starting iron tablets immediately when she has been told by a neighbour to 'just take iron'?