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PA14.1-2 | Peripheral Smear in Microcytic Anaemia: Hands-on Interpretation — Summary & Reflection
REFLECT
Practical drill for your CP posting this week:
You will encounter smears in the Clinical Pathology (CP) laboratory. When you sit down at the microscope:
- Start at 10×. Scan the feathered edge. Get the distribution. Resist the urge to go to oil immediately.
- Move to 40×. Find your monolayer. Pick 4 fields. Apply the four-parameter framework: size, colour, shape, content.
- Then — and only then — go to 100× oil to confirm what you saw at 40× and check for inclusions.
- Write one sentence before you look at the CBC: What does this smear tell me? Then check if the CBC supports it.
- Don't be afraid to spend 3 minutes at low power. Most diagnoses are made at 10–40×. Oil immersion is confirmation, not discovery.
The goal of this posting is to build a pattern library in your visual cortex. Each smear you examine — even a normal one — trains your eye to recognise when something is wrong. There is no shortcut to this. The smear is a skill.
Reflection question: Think of a real patient in your ward with anaemia. If you had their peripheral smear in front of you right now, what would be the first three things you look for, and why those three first?
KEY TAKEAWAYS
Peripheral Smear in Microcytic Anaemia — Systematic Summary
Scanning sequence: 10× (distribution) → 40× (field selection, initial morphology) → 100× oil (confirm, inclusions). The '4-field rule': 4 fields before concluding.
Four-parameter framework: Size (microcytosis vs lymphocyte nucleus) | Colour (central pallor >1/3 = hypochromia) | Shape (pencil cell, target cell, teardrop) | Content (basophilic stippling, Pappenheimer bodies)
Disease pattern matrix:
| Feature | IDA | Thal Trait | Sideroblastic | Lead Poisoning |
|---|---|---|---|---|
| Microcytosis | ++ | +++ | +/- (dimorphic) | + |
| Hypochromia | ++ | + | ++ (in small pop.) | + |
| RDW | HIGH | LOW/Normal | VERY HIGH | HIGH |
| Pencil cells | ++ | - | - | - |
| Target cells | + (few) | +++ (prominent) | - | - |
| Dimorphic pop. | - | - | +++ (pathognomonic) | + |
| Basophilic stippling | - | + (fine) | + | +++ (coarse) |
| Pappenheimer bodies | - | - | ++ | - |
Key mnemonics:
- IDA = Pencil cells + High RDW + Hypochromia + few target cells
- Thal trait = Target cells prominent + Low RDW + disproportionate microcytosis + high RBC count
- Sideroblastic = Dimorphic population (pathognomonic) + very high RDW
- Lead = Coarse stippling + occupational/exposure history
Next investigation after smear: IDA → serum ferritin | Thal trait → HPLC (HbA2) | Sideroblastic → bone marrow + Perls' stain | Lead → whole blood lead level