PA17.1 | Aplastic Anaemia & Bone Marrow Examination — Summary & Reflection

REFLECT

Return to the opening clinical vignette. You now have all the tools to fully analyse it.

1. List the three features in the blood count that confirm pancytopenia, and state which is most immediately life-threatening.
2. The smear showed normocytic-normochromic RBCs and NO blasts. How does this narrow your differential?
3. The patient had NO splenomegaly and NO lymphadenopathy — which two diagnoses does this single finding help exclude?
4. If you requested a bone marrow examination and received a 'dry tap' — what would that mean for aplastic anaemia as your diagnosis?
5. What single investigation would be MOST useful to classify severity and decide between stem-cell transplant and immunosuppression?

Write your answers before looking at the summary — this consolidates the diagnostic reasoning you will use at the bedside.

KEY TAKEAWAYS

Aplastic anaemia is pancytopenia + hypocellular marrow with no blasts, fibrosis, or infiltration.

Aetiology: Idiopathic (~70%); acquired (chloramphenicol, benzene, radiation, seronegative hepatitis); inherited (Fanconi anaemia — DNA repair defect; dyskeratosis congenita — telomerase mutation).

Pathogenesis: Predominantly immune-mediated cytotoxic T-cell destruction of stem cells (responds to immunosuppression); intrinsic stem-cell defect in inherited forms.

Key clinical marker: NO hepatosplenomegaly, NO lymphadenopathy — if present, revise diagnosis.

Peripheral blood: Normocytic-normochromic anaemia, reticulocytopenia, pancytopenia, relative lymphocytosis, NO blasts.

Severity: Camitta criteria — severe = hypocellular marrow + two of [neutrophils <0.5×10⁹/L, platelets <20×10⁹/L, reticulocytes <20×10⁹/L].

Bone marrow examination indications: Pancytopenia, suspected leukaemia/lymphoma/myeloma, staging, marrow infiltration, monitoring treatment.

Sites: Posterior iliac crest (aspirate + trephine); sternum (aspirate only — NO trephine).

Aspirate vs trephine: Aspirate = cell morphology, cytogenetics; Trephine = architecture, cellularity, fibrosis.

Dry tap = fibrosis or packed marrow; always follow with trephine.

Cellularity estimate: ≈ 100 − age; aplastic anaemia = <25% (age-adjusted).

Key differentials: Hypocellular MDS (dysplasia present), aleukemic leukaemia (blasts in marrow), megaloblastic anaemia (macrocytosis, hypersegmented neutrophils).