CONCENTRATION: Introduction (cont.)

Formalin-Ethyl Acetate Sedimentation Concentration

By centrifugation, this concentration procedure leads to the recovery of all protozoa, eggs, and larvae present; however, the preparation contains more debris than is found with the flotation procedure. Ethyl acetate is used as an extractor of debris and fat from the feces and leaves the parasites at the bottom of the suspension. The formalin-ethyl acetate sedimentation concentration is recommended as being the easiest to perform, allows recovery of the broadest range of organisms, and is least subject to technical error.

The specimen must be fresh or formalinized stool (5 or 10% buffered or nonbuffered formalin or sodium acetate-acetic acid-formalin [SAF]). Polyvinyl alcohol (PVA)-preserved specimens can also be used.