Microscopic testing of feces is performed to identify the presence of leukocytes, fats, and parasites. It may be used as a screening test or to support the findings of other diagnostic interventions.
A microscopic stool test for leukocytes, especially neutrophils and monocytes, is performed as an initial evaluation for diarrhea of unknown etiology. Although the presence of leukocytes can help determine the cause of diarrhea, there are many types of diarrhea that do not exhibit an increase in fecal leukocytes.
Normal Findings. Leukocytes are not present in stool.
Variations from Normal. Leukocytes in stool, coupled with the presence of diarrhea, is diagnostic for bacterial diarrhea that involves the intestinal wall. Ulcerative colitis also exhibits leukocytes in the stool.
Microscopic testing for fats is performed to identify the amount of fat present in feces. Using a microscopic exam, the laboratory professional is able to determine the number and size of fat droplets present in feces, as well as the type of fats present. The types of fats in feces include triglycerides, fatty acids, and fatty acid salts. The presence of fat in the stool is called steatorrhea, a possible sign or symptom of serious malabsorption syndromes and diseases such as celiac sprue and cystic fibrosis.
Microscopic identification of fats in feces is limited since it only detects the presence of excessive fat and the nature of the fat. In order to adequately assess steatorrhea, the patient must be placed on a fat-controlled diet and collect stool samples over a seventy-two-hour period. After the collection is completed, the feces is analyzed to determine what percentage of the total solid fecal material is fat.
Fat <60 normal-sized droplets
Triglycerides 1-5% Fatty acids 5-15%
Variations from Normal. Excessive triglyceride levels in feces are associated with pancreatic enzyme deficiency. Increased fatty acids with normal triglyceride levels are seen in malabsorption syndromes.
Microscopic examination for parasites is performed when there is a suspicion of parasitic infestation that may be causing gastrointestinal disorder or distress. Fecal specimens collected for parasite testing should be transported to the lab immediately. Parasites frequently found in feces are tapeworms, hookworms, pinworms, amoebae, and protozoa. In some circumstances multiple fecal specimens are collected over a period of time to determine the presence of parasites. Other methods of obtaining fecal specimens include the use of a rectal swab or the cellophane tape test.
The cellophane tape test is used to collect a specimen from the rectal area of the patient. The specimen is then examined for pinworms. This test should be done early in the morning or overnight before the patient has bathed or defecated. A strip of clear cellophane tape is applied to the perineal region; the tape is removed and attached to a slide for microscopic evaluation.
Variations from Normal. Parasitic infestation is associated with a wide variety of diseases. Protozoa infestations can cause dysentery, which may lead to perforation and peritonitis. Hookworms attach themselves to the duodenal lining and nourish themselves on the blood of the host, often resulting in anemic conditions. Pinworms cause marked irritation and itching of the skin around the anus, and tapeworms can cause diarrhea, epigastric pain, and weight loss.
Interfering Circumstances. Failure to follow proper specimen collection procedures alters the outcome of fecal tests.
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