CONCENTRATION: Procedure Limitations

1. Results obtained with wet smears (direct wet smears or concentrated specimens) should usually be confirmed by permanent stained smears. Some protozoa are very small and difficult to identify as to species with just the direct wet smears. Also, special stains are sometimes necessary for organism identification (Cryptosporidium parvum, microsporidia).

2. Confirmation is particularly important in the case of E. histolytica/E. dispar versus E. coli.

3. Certain organisms (G. lamblia, hookworm eggs, and occasionally Trichuris eggs) may not concentrate as well from PVA-preserved specimens as they do from those preserved in formalin. However, if there are enough G. lamblia organisms present to concentrate from formalin, then PVA should contain enough for detection on the