Analyzers flag; smears explain. Even in a laboratory with modern hematology analyzers and digital morphology, the peripheral blood film is still how we confirm a suspicious flag, catch platelet clumps, spot blasts or schistocytes, and recognize malaria parasites. And a smear is only as good as the routine behind it.
Start with the specimen
- Use well-mixed EDTA blood, and make films as soon as practical. Prolonged storage in EDTA causes artifacts such as crenated red cells and changes in white cell appearance.
- Mix gently by inversion right before you make the film. Settled samples give misleading distributions.
- Label the frosted end in pencil with the patient identifiers before you spread.
The wedge technique, done consistently
- Place a small drop of blood (about 2–3 mm) near the frosted end of a clean slide.
- Hold the spreader slide at roughly 30–45°, let the drop spread along its edge, then push forward in one smooth, steady motion.
- Adjust the angle for the sample. A high hematocrit (thick blood) needs a lower angle; anemic samples need a steeper angle.
- Aim for a film that covers about two-thirds to three-quarters of the slide, with a smooth feathered edge and no ridges, holes or streaks.
- Air-dry quickly. In humid Philippine laboratories, slow drying produces water artifacts. A small fan helps.
Staining
Romanowsky stains (Wright, Wright-Giemsa) are standard. Whatever your method, fix promptly, follow fixed timings, and check stain quality daily: red cells should be pinkish-orange, neutrophil granules lilac, nuclei purple. Blue-tinged films usually mean the buffer pH is too high or the film is too thick; overly pink films suggest an acidic buffer or over-washing.
Reading the film systematically
- Low power (10×): scan the whole film, especially the feathered edge and sides, for platelet clumps, large abnormal cells, rouleaux and parasites.
- Find the monolayer, where red cells just touch without overlapping. This is your reading area.
- Oil immersion (100×): perform the differential, assess red cell morphology, and estimate platelets.
- Correlate with the analyzer. Does the platelet estimate roughly agree with the count? Does the white cell distribution make sense?
A common platelet estimate is the average number of platelets per oil-immersion field in the monolayer, multiplied by a factor of about 15,000–20,000 per µL. Validate the factor for your own microscopes and field size.
Report in a common language
Consistency between MedTechs is as important as accuracy. The International Council for Standardization in Haematology (ICSH) published recommendations for naming and grading red cell, white cell and platelet abnormalities (Palmer et al., 2015). Adopting a shared grading scheme, for example for schistocytes or poikilocytes, means that “2+” means the same thing on every shift.
If two MedTechs read the same slide and report it differently, the problem is not the slide. It is the routine.
Build a daily habit
- Review a few smears each morning against analyzer flags, even when not required.
- Keep a teaching set of interesting slides and photos for new staff.
- Hold short morphology huddles for unusual cases.
- Use proficiency testing photos as a regular team exercise.
References
- Palmer L, et al. ICSH recommendations for the standardization of nomenclature and grading of peripheral blood cell morphological features. Int J Lab Hematol. 2015;37:287–303: doi.org/10.1111/ijlh.12327
- The Blood Project, ICSH smear morphology summary: thebloodproject.com
- Korean Society for Laboratory Hematology, guideline for peripheral blood smear reporting: synapse.koreamed.org
