Lab Safety and Specimen Collection Flashcards
Potential risks in parasitoloy lab
- Ingestion of eggs/ova
- Skin penetration of infective larva
- Infection of non-parasitic agents
True or False: fixed stool specimens in formalin are risk-free and non-infectious because of the fixative
False
Has a thick outer layer made up of albumin
Ascaris lumbricoides
Container for fecal specimen
Clean, wide-mouthed containers
Capacity of fecal containers
0.5 pint or approx. 240 mL
How many specimens within how many days should be collected for routine fecalysis?
3 specimens collected within 6-7 days (no more than 7 days)
Every other day is collected
How many specimens within how many days should be collected for intestinal amebiasis?
No more than 6 specimens collected within 10 days
How many weeks is the patient deferred from fecalysis if they are taking anti-protozoan drugs?
3-4 weeks
How many weeks is the patient deferred from fecalysis if they are taking anti-helminthic drugs?
5-6 weeks
Which drugs should be a cause of deferment for 1 week?
o Antacids
o Anti-diarrheals
o Barium
o Bismuth
o Laxatives
Usually decreases the number of protozoans for several weeks
Antibiotics
Size of formed stool that should be used
thumb-sized
How much watery stool should be used
5-6 tablespoons
How much time before trophozoites die?
30 minutes - 1 hour
What should be the temperature of the refrigerator used for stool samples?
3-5 degrees celsius (4 degrees celsius is the most optimal)
Does not preserve morphology (has time limitations)
Formalin
Stool to fixative ratio for formalin
1:3
Concentration of formalin that is recommended for protozoan cysts
5%
Concentration of formalin that is recommended for helminth eggs and larva
10%
Percentage of the stock solution of formalin
40%
What solution can buffer formlin to preserve morphological characteristics of organisms
Sodium phosphate
Morphology is preserved but not motility
Schaudinn’s solution
Used to preserve fresh stool in preparation for staining the stool smears
Schaudinn’s solution
Contains mercuric chloride (highly toxic to humans; problems of mercury disposal may arise)
Schaudinn’s solution
The best option for permanent staining
mercuric chloride
Not a fixative but an adhesive
Polyvinyl alcohol (PVA)
o Normally incorporated into the Schaudinn’s solution (actual fixation is done by the Schaudinn’s)
Polyvinyl alcohol (PVA)
A plastic resin which serves to adhere a stool sample onto a slide
Polyvinyl alcohol (PVA)
Combination of fixative and temporary stain
Merthiolate-Iodine-Formalin (IMF)
Useful for the fixation of intestinal protozoans, helminth eggs, and larvae
Merthiolate-Iodine-Formalin (IMF)
Has glacial acid that helps lyse the cells and albumin-glycerol which sticks the sample to the slide
Sodium acetate-acetic acid formalin (SAF)
Has the advantage of not containing mercuric chloride
Sodium acetate-acetic acid formalin (SAF)
not as sharp after staining compared to PVA or Schaudinn’s solution
Sodium acetate-acetic acid formalin (SAF)
A liquid fixative with a long shelf-life
Sodium acetate-acetic acid formalin (SAF)
What type of stool sample should be used for direct stool examination?
fresh sample
What type of stool sample should be used for concentration methods?
Preserved and fresh sample
What type of stool sample should be used for permanent smear?
preserved sample
Possible observation of trophozoites motility
Fresh stool
Can be used for direct wet exam, concentration methods, permanent staining, immunoassays, special staining, etc.
Fresh stool
Presents good morphology of the organism as some preservative may alter the morphology of parasites
Fresh stool
May have excessive lag time between stool fixation or processing
fresh stool
Organism morphology is preserved when lag time between stool passage and fixation is short
preserved stool
How much time is permitted to process a watery sample?
30-60 mins
How much time is permitted to process a formed sample?
up to 24 hours
What is predominant in formed sample?
Cysts
What is predominant in watery sample?
trophozoites
What consistency of stool samples has equal amounts of trophozoites and cysts?
soft & loose
