Question

Chapter 10: Clinical Laboratory Procedures Case Study

A request for “ova and parasites” was received in the laboratory in the late afternoon. The specimen consisted of one polyvinyl alcohol (PVA) vial and one 10% formalin vial. The specimen label included the patient’s name, the doctor’s name, and the date collected. There was a note attached requesting “special attention for amoeba.” The technologist noted that the specimen vials contained material that was yellowish, opaque, and appeared chalky looking.

1. The medical laboratory scientist (MLS) checked the patient’s history and found that he had been scheduled for a lower G.I. tract x-ray series that morning. What conclusion would be drawn from this information and what action should be taken?
   1. Process the specimen as usual.

2. Reject the specimen; barium is present in the specimen.

3. Reject the specimen; identification information is incomplete.

4. Reject the specimen for reasons B and C.

2. What effect does barium have on the specimen?

1. It makes observation of parasites impossible.

2. It kills all eggs, cysts, and trophozoites.

3. It makes the specimen hazardous for workers.

2. 4. It confuses the MLS because it looks like yeast.
3. A week later, a new and properly labeled specimen arrived for parasite examination at 2 p.m.

The collection time on the unpreserved liquid specimen was 9 a.m. The comment on the order stated, “Rule out Giardiasis.” How should the MLS handle this specimen?

1. Process as usual; a proper specimen was submitted.

2. Immediately look for trophozoites in a wet mount.
3. Process as usual, noting that trophozoites might not be visible because the sample was not submitted when collected.
4. Reject the specimen because it was not preserved when collected.

4. Two days later a new, fresh, correctly labeled specimen and a PVA tube containing the patient’s feces were submitted for parasitic examination. The specimen, collected at 10 a.m., arrived in the laboratory at 10:30 a.m. Select the correct sequence used to properly process this specimen.
   1. Prepare smears for trichrome and modified acid-fast stains; concentrate and read results from 10% formalin preparation; stain and read the trichrome smears.
   2. Prepare and read the direct mount made from fresh feces; prepare trichrome smears from the PVA tube; concentrate and read results from the PVA tube.
   3. Concentrate and read results from 10% formalin preparation; prepare and read the direct mount made from fresh feces; prepare, stain, and read the trichrome smears from the PVAtube.
   4. Prepare and read the direct mount made from fresh feces; prepare smears for trichrome and modified acid-fast stains; concentrate and read results from 10% formalin preparation; stain and read the trichrome and acid-fast smears.

Answer 1

The ova and parasite exam is used to detect the presence of parasites in a stool sample and help diagnose an infection of the digestive system (gastrointestinal, GI tract). Since there are many causes of GI infections, an O&P may be used in conjunction with other tests, such as a gastrointestinal (GI) pathogen panel or stool culture, to help establish a diagnosis.

Many GI infections resolve with no specific treatment, with only supportive care, and may not require testing. In otherwise healthy individuals, the infections are considered common illnesses that are not serious and sometimes thought of as "food poisoning" or "stomach flu." However, there are cases where it is useful to perform testing that identifies the cause of the GI infection – to guide its treatment, eliminate its source, and limit its spread.

Other tests for parasites may be used in conjunction with an O&P to help make a diagnosis. A healthcare practitioner may order a Giardia, Cryptosporidium, or Entamoeba histolytica antigen test if it is suspected that one of these parasites may be causing a patient's infection. These tests detect protein structures on the parasites and can identify an infection, even if no actual parasites or ova are seen in the stool. Since antigen tests only detect a few specific parasites, they are not replacements for the complete O&P, which will detect a wider variety of parasites.

The O&P is ordered when a person is suspected of having ingested contaminated food or water and has signs and symptoms of a GI infection, such as:

• Prolonged diarrhea
• Abdominal pain, cramping
• Nausea, vomiting
• Blood and mucus in the stool
  A barium X-ray is a radiographic (X-ray) examination of the gastrointestinal (GI) tract. Barium X-rays (also called upper and lower GI series) are used to diagnose abnormalities of the GI tract, such as tumors, ulcers and other inflammatory conditions, polyps, hernias, and strictures. The use of barium with standard X-rays contributes to the visibility of various characteristics of the GI tract. Barium is a dry, white, chalky powder that is mixed with water to make barium liquid. Barium is an X-ray absorber and appears white on X-ray film. When instilled into the GI tract, barium coats the inside wall of the esophagus, stomach, large intestine, and/or small intestine so that the inside wall lining, size, shape, contour, and patency (openness) are visible on X-ray. This process shows differences that might not be seen on standard X-rays. Barium is used only for diagnostic studies of the GI tract. that's why the sample is rejected because Barium is present in the sample which makes it impossible for the detection of Ova and parasites.
• After a week later the sample produced was unpreserved that's why sample was rejected. A fresh stool sample transported to the lab within 2 hours or a preserved stool sample is used for testing Ova and parasites

• Collection of stool for parasite examination should always be performed before barium is administered to a patient for radiologic exams. Stool specimens containing the opaque, chalky suspension are unacceptable, and intestinal protozoa may be masked for 5 to 10 days after ingestion of barium. Other substances, such as castor oil or mineral oil, bismuth, antibiotics, including antimalarial medication, and nonabsorbable antidiarrheal preparations, may interfere with parasite recovery, and collection should be postponed for 5 to 10 days after administration to allow clearance of these substances.

  Specimen Collection, Processing, and ShippingThere are many stool collection methods available for specimens suspected of containing parasites. When collection methods are selected, a thorough understanding of the advantages and disadvantages of each must be reviewed. Unless the stool specimens are properly collected and processed, these infections may not be detected. Therefore, specimen rejection criteria have become very important for the best results.

  Fecal specimens should be collected in clean, wide-mouth containers with tight-fitting lids. The specimen should not be contaminated with water or urine, which may contain elements that can be mistaken for fecal parasites. Stool specimens should be placed in leak-proof bags when being transported to the laboratory for analysis. If postal delivery services are used, any diagnostic specimen must be packed according to national or international regulations (e.g., labeling with UN code 3373, the three-container approach) for packaging and shipping of biological specimens. Specimens need to be labeled with the proper patient identifiers, including patient's name and identification number along with the time and date of specimen collection. The specimen must also be accompanied by a request form indicating which laboratory procedures should be performed. Any additional relevant information should be included with the specimen submission.

  It is recommended that multiple stool samples be examined prior to ruling out a parasitic infection. Historically, three specimens collected on alternate days within a 10-day period should be examined; however, some may argue that one or two stool exams are adequate. Many organisms, particularly intestinal protozoa, do not appear in the stool in consistent numbers; concentrations of trophozoites and cysts may vary on a daily basis. Physicians should be aware that the probability of detecting clinically relevant parasites in a single specimen may be as low as 50 to 60% but is >95% if three samples are examined by O&P

• Microscopic examination (routine permanent-stain smears).Detection and definitive identification of the protozoan trophozoites and cysts are best accomplished with the use of a permanent stained smear. Nuclear and cytoplasmic characteristics are enhanced with staining, allowing for organism recognition and identification. There are a number of staining techniques that can be used; however, the trichrome and iron-hematoxylin stains are most widely used. The permanent stain is examined using oil immersion objectives (100×), and a minimum of 300 fields should be examined before the result is determined to be negative. If organisms are seen after a shorter examination, a complete examination of 300 fields is recommended for the detection of other organisms that may be present in lower numbers. Permanent stains are not recommended for the identification of helminth eggs and larvae. These organisms often stain too darkly or are distorted, making identification difficult.

  Wheatley's trichrome stain.Wheatley's trichrome stain is a modification of the Gomori trichrome tissue stain and is used for routine fecal staining. Protozoan organisms will readily be seen on the trichrome stain. The fecal specimen is smeared onto a microscope slide. It is allowed to air dry prior to being stained. The slides are passed through a series of solutions, taking less than 1 h to stain. The stain is easy to perform and allows detection of protozoan trophozoites and cysts, white blood cells, red blood cells, Charcot-Leyden crystals, yeasts, and fecal debris. The color contrast (variations of red, blue, purple, and green) with the trichrome stain is more distinct than with the iron-hematoxylin stain, allowing for easier differentiation between organisms and artifacts. Although fecal specimens in preservatives can be stained with trichrome stain, PVA, modified PVA, and the newer nonformalin, non-PVA preservatives yield the best results.

  Iron-hematoxylin.There are many modifications of the iron-hematoxylin stain; however, the two most commonly used are the Spencer-Monroe and Tompkins-Miller procedures. Iron-hematoxylin was the stain used for most of the original descriptions of the intestinal protozoans. The stool smears are air dried and stained through a series of solutions. The contents of the specimen stain shades of grayish blue. Both methods can be used to stain fecal specimens in most preservatives, including SAF and merthiolate-iodine-formalin fixative (MIF). Other stains include Eco-Stain or the iron-hematoxylin–modified acid-fast combination stain.

• Prepare and read the direct mount made from fresh feces; prepare smears for trichrome and modified acid-fast stains; concentrate and read results from 10% formalin preparation; stain and read the trichrome and acid-fast smears. is the procedure for studying the specimen