There are three standard methods of fecal examination for ova and parasites: direct examination, concentration methods followed by direct examination, and permanent stained slides prepared after concentration. Concentration techniques are useful on all types of stool specimens but especially on formed stools or soft stools. Concentration techniques detect larvae, ova, and protozoan cysts. Direct wet mounts can also be performed on all types of stools and also can detect larvae, ova, and protozoan cysts, but will not detect them as frequently as concentration techniques (in one study, only half as often). However, direct wet mount occasionally will detect some ova and protozoan cysts missed by concentration techniques. Permanent stained slide preparations are designed to detect protozoan cysts and trophozoites rather than ova or larvae, and should be performed on all very soft or liquid stools. Stained slides in addition to concentration plus direct examination are essential for optimal detection of E. histolytica and G. lamblia. In several reports, concentration techniques yielded about 50%-60% positive results for these two protozoans (literature range, 45%-74%), whereas stained smears yielded about 75%-85% positive results (literature range, 59%-95%). In another study, nonfixed direct wet mounts detected only 5% of trophozoites, whereas permanent stain detected about 60%.