PA18.1-2 | Reactive Leucocytosis, Leucopenia & Lymphocytosis — Summary & Reflection

REFLECT

Think about a patient you might see in any medical ward in India:

A 45-year-old diabetic man is admitted with fever and productive cough for 10 days. His WBC is 22 × 10⁹/L with 88% neutrophils, band forms present, and toxic granulation noted on the blood film. Blood culture grows Klebsiella pneumoniae.

Using what you have learned today:
1. Name three morphological findings that tell you this is a reactive (not malignant) picture.
2. What would you expect his LAP score to be?
3. If his WBC were 55 × 10⁹/L instead of 22, what diagnosis would you need to exclude, and which single test would most quickly distinguish the two?

Write your answers before checking. This scenario is structurally identical to examination MCQs and clinical SAQs.

KEY TAKEAWAYS

Core framework — Reactive White-Cell Changes:

Leucocytosis (WBC > 11 × 10⁹/L):
- Always interpret the differential, not just the total.
- Neutrophilia: bacterial infection, inflammation, steroids, tissue necrosis.
- Morphological markers of reactive neutrophilia: left shift, toxic granulation, Döhle bodies.
- Leukaemoid reaction (> 50 × 10⁹/L): reactive; high LAP, no basophilia, identifiable cause.
- CML: low LAP, basophilia, splenomegaly, Philadelphia chromosome — not a reaction.
- Leukoerythroblastic picture = immature WBCs + NRBCs → marrow infiltration until proven otherwise.

Leucopenia (WBC < 4.0 × 10⁹/L) / Agranulocytosis (ANC < 0.5):
- Drugs (especially idiosyncratic: clozapine, carbimazole), viral infections, autoimmune, marrow failure, hypersplenism.
- Fever in agranulocytosis = emergency.

Lymphocytosis:
- Reactive: EBV/CMV mononucleosis (atypical lymphocytes, monospot), pertussis (very high count), TB.
- Atypical lymphocytes = reactive T cells, not malignant.
- Neoplastic: monotonous, monoclonal, persistent — flow cytometry confirms.

Other lines:
- Eosinophilia: NAACP + drugs.
- Monocytosis: chronic granulomatous disease (TB, SLE, IBD).
- Basophilia: always suspect myeloproliferative disease (CML).

Next: SDL 2 explores acute leukaemias; SDL 3 covers chronic myeloid and lymphoid neoplasms.