Ova and Parasite (O&P) Examinations

Microscopic Examination - Ova and Parasite Examination

The permanent stained smear is not recommended for staining helminth eggs or larvae; they are often too dark (excess stain retention) or distorted. However, occasionally they may be recognized and identified. The wet smear preparation from the concentrate is the recommended approach for identification of helminth eggs and larvae.
The smear should be examined with the oil immersion lens (100 x) for the identification of protozoa, human cells, Charcot-Leyden crystals, yeast cells, and artifact material. Quantitation of these cells and other structures is normally done from the examination of the permanent stained smear, not the wet smear preparations (direct wet smear, concentration wet smear).
This high-magnification (oil immersion; total magnification of x 1,000) examination is recommended for protozoa, particularly for confirming species identification.
If the viewer wants to screen the smear with low magnification (10 x objective), one might see eggs or larvae; however, this is not recommended as a routine approach.
In addition to helminth eggs and larvae, I. belli oocysts are best seen in wet preparations (concentration wet smears prepared from formalin-preserved, not PVA-preserved, material).
C. parvum oocysts will generally not be recognized on an iron hematoxylin-stained smear (acid-fast stains or the immunoassay reagent kits are recommended).