Juicio: para tomar decisiones difíciles en poco tiempo y con datos imprecisos y/o ambiguos

Specimens should be collected and handled in such a manner that they arrive at the laboratory in good condition for the identification of protozoans and helminths.

Frequently, intestinal parasites are diagnosed or ruled out based on examination of fecal specimens. However, perianal swabs, liver and duodenal aspirations, or duodenal contents may also be received for examination of intestinal parasites.

MD0841 2-29

(1) Number of samples. Recovery of intestinal parasites is enhanced by the collection of three or more specimens at intervals of two to three days apart. The time period between the collection of samples is necessary to compensate for the periodicity of the life cycles of the parasites.

(2) Specimen containers. The most suitable container for collection and transportation of stool specimens is one that has a wide leak-proof cup, bottle, or carton that is clean and dry. This container should not be reused. It should be disposable.

(3) The label. Certain information should be affixed to the container to prevent the mixing of samples.

(a) Patient data. The name of the patient must be clearly written on the container. Other information which should be on the label includes the patient's identification or hospital number, the ward or clinic name, and the name of the attending physician.

(b) Collection data. The date and time of collection as well as the sequence number of the specimen should also be included on the label.

b. Cathartic Induced Samples. Some protozoans and helminthes are passed with more frequency in a loose stool. The use of purgatives (e.g., cathartic or laxatives) has been found to be beneficial in enhancing the recovery of intestinal parasites from constipated patients.

(1) Recommended cathartics. These purgatives are administered in saline solutions. Some examples of these cathartics are:

(a) Sodium sulfate.

(b) Buffered phosphosoda.

(c) Cascara sagrada.

(2) Unsatisfactory cathartics. There are some chemicals that interfere with the examination of the stool specimen. Thus, cathartics containing the following

chemicals should be avoided:

(a) Castor oil.

(b) Mineral oil.

(c) Magnesia compounds.

c. Perianal Samples. Eggs of Enterobius vermicularis (and rarely Taenoid eggs) are deposited around the perianal folds and can be collected by adhering the eggs to the collecting apparatus.

(1) Cellulose-tape slide preparation.

(a) STEP 1: Place a strip of "Scotch tape" about 3/4-inch wide and 3-1/2 inches long on one end of a tongue depressor, sticky side down (give the written instructions to the patient).

(b) STEP 2: Just prior to collection, lift one end of the tape from the depressor and loop it over to expose the sticky surface.

(c) STEP 3: Holding the depressor with the right hand, spread the buttocks with the left hand and press the sticky surface of the tape against several areas of the perianal region.

(d) STEP 4: Either replace the tape on the tongue depressor for

transportation to the laboratory or place the "Scotch tape" on a 25 by 75 millimeter glass slide, sticky side down.

(e) STEP 5: Smooth the tape with cotton or gauze.

(f) STEP 6: Examine the slide under the low power objective of the microscope and confirm findings under the high dry.

(2) Anal swab.

(a) STEP 1: Prepare a paraffin/Vaseline mixture in a 1:4 ratio and coat swabs with the warm mixture. Allow the swabs to cool.

(b) STEP 2: Holding the swab with the right hand, spread the buttocks with the left hand and gently swab the perianal region with the coated swab.

(c) STEP 3: Place the swab in a 13 by 100 tube to which two or three milliliters of xylol has been added. Allow to stand for three to five minutes.

(d) STEP 4: Twirl the swab in the xylol, hold it against the sides of the test tube, and express the liquid; discard the swab.

MD0841 2-31

(3) Duodenal contents. Parasites that inhabit the small intestines are easily overlooked when examining a stool sample. Consequently, when Giardia lamblia or Strongyloides stercoralis are suspected, the duodenal content examination will be the test of choice. Duodenal intubation causes much discomfort to the patient; therefore, it is not a desirable procedure. In its place, the string-capsule technique (described by Beal, et al, in 1970) offers an easy and almost painless method of examining duodenal contents. A gelatin capsule containing a line of 25 centimeters silicon thread covered with rubber and a 75-centimeter soft nylon yarn are used in this procedure. The patient swallows the capsule containing the string and a lead weight that helps the capsule to move to the duodenum (the end of the string that sticks out is held fast by taping it to the patient's neck). After three to five hours, the string is pulled out (the weight separates from the capsule and it is excreted), the portion of the string that has bile-stain contents is scraped off, placed on a slide, and examined for protozoan cysts and trophozoites or helminthes eggs and larvae.

(4) Sigmoidoscopic examinations. When amebiasis is suspected and stool samples are negative, material for examination may be collected by sigmoidoscopy.

The procedure should be performed after a normal bowel movement or two to three hours after administration of a cathartic. The specimen is collected with a pipette rather than with a swab by aspirating material from any visible lesion and from the mucosa.

Examination of sigmoidoscopic material should be done immediately, but fixation can be done with polyvinyl alcohol (PVA) after the wet preparation.

(5) Liver abscesses. Exudates aspirated from the liver may contain cysts and trophozoites of Entamoeba histolytica. The first portion of the specimen does not usually yield organisms, but the second (reddish) portion does. Aspirates should be examined microscopically with wet preparations as well as with permanent stains.