Thick vs Thin film comparison
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Relative merits of thick or thin films in malaria diagnosis
There is no single correct choice of staining, essentially the thin film has many advantages in terms of ease of preparation, staining and identification. In contrast the thick malarial film offers a single but significant advantage: that of superior sensitivity for parasite detection. The images above show the merits of the techniques - the thin film resolves good parasite detail and also the features of the red cell allowing parasite size to be appreciated and any alterations to red cells to be seen and characterised. In contrast, the thick film resolves less parasite detail and no red cell features (in this example) but shows all parasites in a volume that is likely around 6-fold greater than the thin film.
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Thin film appearances P.falciparum
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Thick film appearances P.falciparum
The relative merits and drawbacks of the two approaches are outlined in the table below.
| 1. Sensitivity for detection |
|---|
| Thick film: Higher - can detect lower levels of parasitaemia ~5–10 parasites/µL |
| Thin film: Lower - generally requires ~50 parasites/µL for reliable detection |
| 2. Species Identification |
| Poor: poor - red cell morphology is lost and species-specific features may not be seen |
| Thin film: Good - both parasite morphology and RBC characteristics are assessed |
| 3. Quantification of parasite number |
| Difficult: red cells are not seen so requires estimation and is therefore imprecise |
| Easier: parasites can be counted counted directly and assessed as a proportion of red cells |
| 4. Preparation and staining considerations |
| Less easy: requires air drying and careful spreading and staining to minimise any artefact |
| Easier: films are fixed and stained immediately with clearer morphology of parasites and red cells |