Collection and Handling of Fecal Specimens

The numbers and times of collection for fecal specimens depend somewhat on the diagnosis suspected. As a routine, because some organisms are shed in a variable pattern, it is advisable to examine multiple specimens before excluding parasites. The general recommendation is to collect a specimen every second or third day, for a total of three specimens. From a hospitalized patient, one specimen each day for three days may be more cost effective. 

A number of substances may interfere with stool examination. Particulate materials such as barium, antacids, kaolin, and bismuth compounds interfere with morphologic examination, and oily materials such as mineral oil create small, refractile droplets that make examination difficult. Antimicrobial agents, particularly broad-spectrum antimicrobial agents, may suppress amebae. If any of these substances have been used, specimens should not be submitted until the substances have been cleared (generally 5 to 10 days). A fecal specimen may appear satisfactory by gross examination when there is still barium, etc., which can interfere with microscopic examination. 

Clinical information such as the suspected diagnosis, travel history of the patient, and clinical findings should be included on the requisition. In addition, the time the specimen was passed and the time it was placed in fixative should be noted. If the specimen is in fixative, the consistency of the original specimen should be stated, or a portion of unfixed specimen should be included with the fixed specimen. 

A laboratory may have specimens placed in fixatives in the home or patient care area immediately after passage, may place portions of specimen in fixatives at the time they are received in the laboratory, or may examine the specimen unfixed. Many laboratories use a combination of these methods depending on the location of the patient, consistency of the specimen, time of day, and laboratory work load. Prompt examination or fixation is particularly important for soft, loose, or watery specimens, which are most likely to contain protozoan trophozoites. 

Formed specimens, which are likely to contain protozoan cysts or helminth eggs or larvae, can remain satisfactory for a number of 

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