CHAPTER 2: Specimen Collection and Processing Flashcards
2 general components of O&P
Macroscopic and Microscopic
Helminth stages
Cestodes Eggs Proglottids Larvae (L1, L2, L3) Adult worms Nematodes Trematodes
What is the typical stool collection?
3 specimens that are:
- collected every other day
- total of (3 specimens) collected in 10 days
Clean, wide-mouthed containers ENSURES?
moisture retention
what is the specimen exception for Amebiasis diagnosis
6 specimens in 14 days is acceptable
Specimen collection for patients with therapy of interfering substances
Collect specimen prior to therapy or
5-7 after completion
What are the interfering substances?
Barium
Bismuth
Mineral Oil
Specimen collection for patients with antibiotics or anti-malarial medication
Delayed for 2 weeks following therapy
Standards in stool collection
Clean, watertight container w/ tight fitting lid
2-5g “size of a walnut”
Urine is not allowed to contaminate stool
Should not be retrieved from toilet bowl water
Why stool specimens should not be contaminated by urine?
It may destroy parasites needed for diagnosis
Why stool specimens should not be retrieved from toilet bowl water?
Toilet bowl water contains free-living protozoa and nematodes
Parasite that can be destroyed by water (like eggs and amebic trophozoites)
Schistosome
What else can contaminate the stool and makes it difficult for examination?
Toilet paper
What labels and standards should be seen in a specimen container?
Patient's name Identification number Physician's name Date and time Age and sex Zip lock bag for transport Form of requisition paper Indicating tests required OTHERS: Suspected diagnosis travel history clinical findings prior infections
In testing fecal specimen, liquid stool should be examined within how many minutes?
30 mins of passage
In testing fecal specimen, semi-formed stool should be examined within how many hours?
1 hour of passage
In testing fecal specimen, formed stool should be examined within how many hours?
24 hours following collection
What should be done if the standard minutes for fresh examination is not met?
Specimen is placed into preservative by using fixatives.
2 diagnosis of parasitic infections:
- Definitive diagnosis
2. Presumptive diagnosis
It demonstrates humoral immune response of the individual (antigen-antibody)
Presumptive diagnosis
Actual demonstration of parasites and parasitic components
Definitive diagnosis
In definitive diagnosis, tapeworms are?
segmented
What are the segments or parasitic components of tapeworms?
Scolex
Neck
Proglottids
Standard refrigerator temperature for stool specimen
3-5 celcius
- It preserves morphology of protozoa,
- prevent further development of helminth egg & larvae
- for successful recovery of parasites
Fixative
Ratio for fixative preservation
3:1
What are the different kinds of fixatives for specimen preservation?
- Formalin
- Schaudinn solution
- Polyvinyl Alcohol (PVA)
- Merthiolate-idodine-formalin
- Sodium acetate formalin (SAF)
The all purpose fixative.
Formalin
Percentage of formalin to preserve protozoan cysts
5%
Percentage of formalin to preserve helminth eggs and larvae
10%
3 advantages of formalin
easy to prepare
preserves for several years
long shelf life
Disadvantages of formalin
does not preserve parasite morphology for permanent smears (FADE w/ TIME)
Considered potential health hazard
- A preservative that plastic powder acts as adhesive for stool slide staining.
- often combined with?
Polyvinyl Alcohol (PVA) with Schaudinn solution
A preservative used for staining that contains:
- Zinc sulfate
- copper sulfate
- Mercuric chloride (as a base)
Schaudinn solution
Advantage and disadvantage of PVA
Long shelf life at room temp.
Mercuric chloride is a potential health problem
Many laboratories choose 2 vial systems such as:
Formalin vial for concentration
PVA vial for stained slide
A preservative that is:
- M&I staining
- fixation of intestinal protozoa, helminth eggs, and larvae
- Thimerosal
Merthiolate-iodine-formalin
A preservative that is:
- an alternative for PVA/Schaudinn’s
- concentration and permanent smear
- used with modified acid-fast stain (to detect coccidian oocysts)
Sodium Acetate Formalin (SAF)
Disadvantages of SAF
adhesive properties are not good and needs Albumin
not as clear morphology like mercury-base
stained smear with iron hematoxylin is better
The analytic phase of laboratory
Processing
Important factors considered in specimen processing
Consistency and color
3 distinct procedures for microscopic examinations
Direct wet preparation
Concentrated wet preparation
permanently stained smear
A prep that has a drop of ___% saline on glass slide mixed with unfixed stool
Direct saline wet prep (0.85%)
Lugol’s or D Ántoni’s formula
Direct Iodine wet prep
It minimizes the refraction of glycerin
Malachite Green
Used to clear fecal debri
Glycerin
A prep that uses malachite green or green cellophane soaked in glycerin
Kato thick smear
Kato thick smear is to be examined ____ mins
10-20 mins
Kato thick smear is not for:
thin shelled eggs
protozoan cysts and trophs
has the ability to:
- detect small numbers of parasite
- aggregate parasites present into a small volume of sample
- remove as mush debris
- can be performed on fresh or preserved stool
Concentration methos
2 types of concentration
Sedimentation and Flotation
Most widely used sedimentation technique and based on specific gravity
Formalin-ethyl- acetate sedimentation
This is added to a saline washed formalin - fixed sample
Ethyl acetate
Technique where parasites float with specific gravity of ____?
Zinc sulfate flotation technique (1.18-1.20)
Added to specimen and centrifuge (can be skimmed)
Zinc sulfate
The final procedure for O&P for confirmation and observe detailed features of protozoa by intracellular organelles staining
Permanent stain
2 common stains for routine O&P
Trichrome (wheatly modification)
Iron hematoxylin
