CONCENTRATION: Introduction (cont.)

A flotation procedure permits the separation of protozoan cysts, coccidian oocysts, microsporidian spores and certain helminth eggs and larvae through the use of a liquid with a high specific gravity. The parasitic elements are recovered in the surface film, and the debris remains in the bottom of the tube. This technique yields a cleaner preparation than does the sedimentation procedure; however, some helminth eggs (operculated eggs and/or very dense eggs such as unfertilized Ascaris eggs) do not concentrate well with the flotation method. The specific gravity may be increased, although this may produce more distortion in the eggs and protozoa. Laboratories that use only flotation procedures may fail to recover all of the parasites present; to ensure detection of all organisms in the sample, both the surface film and the sediment should be carefully examined. Directions for any flotation technique must be followed exactly to produce reliable results.