Para Lab 1

• Stool


  The most commonly submitted sample for parasite examinations
• Examination of a stool specimen for ova and parasites (O&P)


  The most common procedure performed in the area of parasitology
• Typical stool analysis


  Performing macroscopic and microscopic techniques on a portion of unpreserved sample when available
• The quality of the results is dependent on the appropriate collection of the specimen
• Specimen handling

  1. Collection

  2. Handling

  3. Preservation

  4. Transport
• Fecal specimens


  Should be collected in clean, wide mouthed/watertight containers with tight-fitting lids, waxed cardboard box (1/2 pint) or matchbox
• Urine should not be allowed to contaminate the stool specimen because it has been known to destroy some parasites
• Stool should not be retrieved from toilet bowl water because free-living protozoa and nematodes may be confused with human parasites and may destroy selected parasites, such as schistosome eggs and amebic trophozoites
• Stool Specimen Containers


  • Figure 1
• Typical stool collection protocol


  One (1) specimen collected every other day or a total of three (3) collected in 10 days except in cases of amebiasis wherein submission of up to six specimens in 14 days is acceptable
• Certain substances and medications also impede detection of intestinal protozoa: mineral oil, bismuth, antibiotics, antimalarial agents and nonabsorbable antidiarrheal preparations
• Stool samples from patients whose therapy includes barium, bismuth or mineral oil


  Should be collected prior to therapy or not until 5-7 days after the completion of therapy (5-10 days for barium)
• Collection of specimens from patients who have taken antibiotics or antimalarial medications

  Should be delayed for 2 weeks following therapy
• Patients who have been treated for protozoan infections


  Are typically checked 3-4 weeks after therapy
• A patient treated for helminth infection

  May be checked 1-2 weeks post therapy and checks for Taenia may be delayed for 5-6 weeks post therapy
• Routine stool examination


  Requires a thumb sized/marble stool of formed stool or about 5-6 tablespoons (10 mL) of watery/diarrheic stool
• The specimen container should be labeled with the patient's name and identification number, the physician's name, and the date and time of sample collection
• Specimen handling


  1. Process and examine as soon as possible after arrival at the laboratory

  2. Examine liquid specimens within 30 minutes of passage

  3. Examine semi-formed specimens within 1 hour of passage

  4. Formed stool specimens can be held for 24 hours following collection
• Liquid specimens


  Contain protozoan trophozoites
• Formed stool specimens


  Contain cysts
• Consistency of stool specimens

  • Liquid
  • Formed
  • Any consistency
• Any consistency of stool specimens may contain helminth eggs and larvae
• Selecting stool specimens for examination

  Pick out liquid/watery stools and/or those with mucus or blood because protozoan trophozoites will destroy rapidly
• Blood and mucus in soft or watery stools may possibly yield the presence of trophozoites
• Gross examination of stool sample


  • Tapeworm proglottids
  • Adult nematodes
• Recovery of the tapeworm scolex on the stool sample following therapy indicates success of treatment
• Stool sample


  Freshly collected, immediately submitted to the laboratory, is the ideal specimen for parasitic examination
• Preservatives


  Used for preservation if stool sample is not immediately submitted
• Fixatives


  Substances that preserve the morphology of protozoa and prevent further development of certain helminth eggs and larvae
• Fixation


  1. Ratio of 3 parts fixative to 1 part stool (3:1)

  2. Specimen must be fixed in the preservative for at least 30 minutes before processing begins
• The choice of fixative/s for O&P use depends on the preference of the laboratory performing the test
• Refrigeration


  Temporary storage of fecal samples at 4-8°C
• Refrigeration


  • Preserves protozoan trophozoites for several days
  • Preserves protozoan cysts for several weeks
  • Can cause desiccation and kill trophozoites with prolonged refrigeration
• Never freeze stool samples nor keep them in incubators
• Refrigerated samples


  Only suitable for antigen testing
• Formalin

  An aqueous solution of formaldehyde, about 37-40% weight in volume
• Formalin

  • All-purpose fixative
  • Buffered with sodium phosphate to help preserve morphological characteristics
• Formalin concentrations used

  • 5% - recommended for preservation of protozoan cyst (trophozoites are destroyed)
  • 10% - recommended for helminth eggs and larvae
• Formalin

  • Advantages: easy to prepare
  • preserves specimens for up to several years
  • long shelf-life
• Formalin

  • Disadvantages: does not preserve morphology for permanent stained smears
  • morphologic details of eggs and cysts may fade over time
  • can interfere with PCR
  • may present as a health hazard