A Giemsa-stained thin film from a febrile patient shows enlarged red cells with amoeboid trophozoites, but no Schüffner's dots. The stain was diluted in buffer of pH 6.4. What is the best action?

Stain a new film with buffer at pH 7.2

Report Plasmodium malariae infection

Make a thicker film and stain it again

Fix the film longer in methanol

What is a Lugol's iodine mount of stool mainly used to show?

Nuclei and glycogen of protozoan cysts

Red colour of acid-fast oocysts

Motility of living trophozoites

Unlike a thin film, a thick blood film for malaria is:

Not fixed, so red cells lyse in the stain

Fixed in 10% formalin before staining

Heat-fixed by passing it over a flame

Fixed in methanol for 2 minutes

Compared with a thin film, the main advantage of a thick blood film in malaria is that it:

Needs no staining before reading

Makes species identification easier

Shows red cell size and stippling

Parasitology: specimens, stool and blood examination

32 Kerala PSC Lab Technician Gr II practice questions on Parasitology: specimens, stool and blood examination, part of Microbiology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A Giemsa-stained thin film from a febrile patient shows enlarged red cells with amoeboid trophozoites, but no Schüffner's dots. The stain was diluted in buffer of pH 6.4. What is the best action?
1. AStain a new film with buffer at pH 7.2
2. BReport Plasmodium malariae infection
3. CMake a thicker film and stain it again
4. DFix the film longer in methanol
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Answer: A · Stain a new film with buffer at pH 7.2
Enlarged red cells with amoeboid trophozoites suggest P. vivax, whose Schüffner's dots should be visible. The dots, and the correct colours of parasite chromatin and cytoplasm, depend on staining at pH 7.2; an acid buffer gives pinkish films in which stippling may not appear. A new film stained with buffer at pH 7.2 should show the dots and confirm the species. P. malariae does not enlarge the red cell.
- B: P. malariae does not enlarge red cells and lacks Schüffner's dots.
- C: Stippling is seen in thin films; a thicker film lyses or crowds the cells.
- D: Fixation time does not decide whether stippling appears.
Question 2 · Easy
Which rapid stain is widely used for thick blood films for malaria parasites?
1. AZiehl-Neelsen stain
2. BGram's stain
3. CAlbert's stain
4. DField's stain
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Answer: D · Field's stain
Field's stain uses two aqueous solutions, Field's A (methylene blue and azure) and Field's B (eosin), and stains a thick film in a few seconds. Because the stains are aqueous, the red cells in the unfixed thick film lyse and the parasites stand out. It suits busy laboratories and clinics where results are needed quickly. Giemsa and Leishman stains are also used, Leishman mainly for thin films.
- A: Ziehl-Neelsen is used for acid-fast bacilli such as Mycobacterium tuberculosis.
- B: Gram's stain classifies bacteria, not blood parasites.
- C: Albert's stain shows the metachromatic granules of Corynebacterium diphtheriae.
Question 3 · Easy
What is a Lugol's iodine mount of stool mainly used to show?
1. ANuclei and glycogen of protozoan cysts
2. BRed colour of acid-fast oocysts
3. CMotility of living trophozoites
4. DSheaths of microfilariae
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Answer: A · Nuclei and glycogen of protozoan cysts
Iodine stains glycogen brown and makes the nuclei and karyosomes of cysts stand out, which helps identify Entamoeba, Giardia and other cysts. It kills trophozoites, so motility must be looked for in a saline mount of the same sample. Saline and iodine preparations are usually made side by side on one slide. Old, faded iodine stains poorly, so the working solution is replaced regularly.
- B: Acid-fast oocysts need a modified Ziehl-Neelsen stain.
- C: Iodine kills trophozoites, so motility is seen only in saline.
- D: Microfilariae are looked for in blood, not stool.
Question 4 · Easy
Unlike a thin film, a thick blood film for malaria is:
1. AFixed in 10% formalin before staining
2. BNot fixed, so red cells lyse in the stain
3. CHeat-fixed by passing it over a flame
4. DFixed in methanol for 2 minutes
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Answer: B · Not fixed, so red cells lyse in the stain
A thick film is dried well but not fixed, so that the water-based stain lyses the red cells (dehemoglobinization) and parasites from many layers of blood become visible. A thin film is fixed in methanol to keep red cells intact for species identification. If a thick film is fixed by mistake, the hemoglobin stays and the film is hard to read. When both films are on one slide, methanol must not touch the thick part.
- A: Formalin fixation is not used for malaria films.
- C: Heat fixation is used for bacterial smears and spoils blood films.
- D: Methanol fixation is used for thin films; it stops a thick film from lysing.
Question 5 · Medium
Compared with a thin film, the main advantage of a thick blood film in malaria is that it:
1. ANeeds no staining before reading
2. BMakes species identification easier
3. CDetects low parasite densities
4. DShows red cell size and stippling
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Answer: C · Detects low parasite densities
A thick film examines many times more blood per field than a thin film, so it picks up low parasitemias and is the better screening test. Because the red cells are lysed, their size, shape and stippling cannot be seen, and parasites look distorted. The thin film is therefore used to identify the species and to count percentage parasitemia. Both films are usually prepared for every patient.
- A: Both films need staining.
- B: Species identification is easier in the thin film.
- D: Red cell size and stippling are lost when the cells lyse; they are seen in thin films.
Question 6 · Medium
In formol-ether concentration of stool, the eggs and cysts are collected from the:
1. AEther layer at the top of the tube
2. BPlug of debris at the interface
3. CSediment at the bottom of the tube
4. DFormalin layer above the deposit
Answer and explanation in LearnFree account
Question 7 · Medium
In Knott's concentration method for microfilariae, venous blood is mixed with:
1. A2% formalin
2. B33% zinc sulfate solution
3. CEthyl acetate
4. DSaturated salt solution
Answer and explanation in LearnFree account
Question 8 · Medium
Saturated salt (brine) flotation is most useful for concentrating which of these?
1. AStrongyloides larvae
2. BUnfertilized Ascaris eggs
3. CHookworm eggs
4. DOperculated fluke eggs
Answer and explanation in LearnFree account
Question 9 · Hard
A 45-year-old man had a barium meal X-ray yesterday. Today his stool is sent for ova, cysts and parasites. What should the laboratory do?
1. ARequest a new specimen after 5-10 days
2. BDilute it in saline and examine it
3. CConcentrate it by formol-ether method
4. DExamine only an iodine-stained mount
Answer and explanation in LearnFree account
Question 10 · Medium
Before a daytime blood examination for microfilariae, a small oral dose of diethylcarbamazine (DEC) is sometimes given. Its purpose is to:
1. ABring microfilariae into peripheral blood
2. BStop the microfilariae from moving
3. CKill adult worms before sampling
4. DMake the sheath stain more clearly
Answer and explanation in LearnFree account
Question 11 · Easy
For motile trophozoites of Entamoeba histolytica, a liquid stool should be examined within:
1. A24 hours of passage
2. B3 days of passage
3. C6 hours of passage
4. D30 minutes of passage
Answer and explanation in LearnFree account
Question 12 · Hard
On a thick film, 150 asexual Plasmodium falciparum parasites are counted against 200 white cells. The patient's total WBC count is 6,000/µL. What is the parasite density?
1. A6,000/µL
2. B9,000/µL
3. C4,500/µL
4. D900,000/µL
Answer and explanation in LearnFree account
Question 13 · Easy
Before Giemsa staining, a thin blood film for malaria parasites is fixed in:
1. AMethanol
2. BHeat over a flame
3. CAcetone
4. D10% formalin
Answer and explanation in LearnFree account
Question 14 · Easy
Which preservative keeps helminth eggs and protozoan cysts in stool intact for later concentration?
1. ASodium fluoride
2. B10% formalin
3. CGlycerol saline
4. D70% ethanol
Answer and explanation in LearnFree account
Question 15 · Medium
A febrile patient's first malaria smear is negative. What is the usual advice?
1. AReport malaria as excluded after one smear
2. BRepeat smears every 6-12 h for 2-3 days
3. CRepeat after 2 weeks of fever
4. DTest only after the fever subsides
Answer and explanation in LearnFree account
Question 16 · Easy
A normal saline wet mount of fresh stool is mainly used to see:
1. ABacterial flagella
2. BAcid-fast oocysts
3. CNuclei of protozoan cysts
4. DMotile trophozoites and eggs
Answer and explanation in LearnFree account
Question 17 · Hard
A falciparum malaria patient has 2.5% parasitised red cells on the thin film, and his RBC count is 3.6 million/µL. How many parasitised red cells are there per µL?
1. A9,000/µL
2. B90,000/µL
3. C25,000/µL
4. D900,000/µL
Answer and explanation in LearnFree account
Question 18 · Easy
For Wuchereria bancrofti microfilariae in India, blood is best collected between:
1. A10 pm and 2 am
2. B6 am and 10 am
3. C4 pm and 8 pm
4. D10 am and 2 pm
Answer and explanation in LearnFree account
Question 19 · Medium
Zinc sulphate flotation (specific gravity 1.18) recovers cysts well but is poor for:
1. AOperculated eggs
2. BGiardia cysts
3. CHymenolepis nana eggs
4. DHookworm eggs
Answer and explanation in LearnFree account
Question 20 · Medium
Before a thick film is reported 'no malaria parasites seen', WHO advises examining at least:
1. A10 oil-immersion fields
2. B20 high-power fields
3. C100 oil-immersion fields
4. DThe whole slide at low power
Answer and explanation in LearnFree account
Question 21 · Medium
Why is the saline mount of stool examined before the iodine mount?
1. AIodine kills and stops trophozoites
2. BIodine dissolves helminth eggs
3. CIodine stains eggs too darkly to identify
4. DSaline shows cyst nuclei better
Answer and explanation in LearnFree account
Question 22 · Medium
A liquid stool for amoebic trophozoites cannot be examined for 3 hours. What should be done?
1. AKeep it in the incubator at 37 °C
2. BAdd normal saline and leave it
3. CRefrigerate the whole sample at 4 °C
4. DFix a portion in PVA fixative
Answer and explanation in LearnFree account
Question 23 · Easy
A thick blood film for malaria is spread to the right thickness when:
1. ANewsprint can just be read through it
2. BIt covers the whole slide evenly
3. CIt shows a feathered edge
4. DRed cells lie singly with no overlap at all
Answer and explanation in LearnFree account
Question 24 · Easy
Why are three stool samples, collected on alternate days, often examined for parasites?
1. ACysts are destroyed on storage
2. BEach sample needs a different stain
3. CParasites are shed intermittently
4. DEggs appear only after a week
Answer and explanation in LearnFree account
Question 25 · Easy
Stool for parasite examination must not be mixed with urine because urine:
1. AKills trophozoites
2. BDissolves helminth eggs
3. CTurns the stool alkaline
4. DAdds free-living larvae
Answer and explanation in LearnFree account

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Parasitology: specimens, stool and blood examination

A Giemsa-stained thin film from a febrile patient shows enlarged red cells with amoeboid trophozoites, but no Schüffner's dots. The stain was diluted in buffer of pH 6.4. What is the best action?

Which rapid stain is widely used for thick blood films for malaria parasites?

What is a Lugol's iodine mount of stool mainly used to show?

Unlike a thin film, a thick blood film for malaria is:

Compared with a thin film, the main advantage of a thick blood film in malaria is that it:

In formol-ether concentration of stool, the eggs and cysts are collected from the:

In Knott's concentration method for microfilariae, venous blood is mixed with:

Saturated salt (brine) flotation is most useful for concentrating which of these?

A 45-year-old man had a barium meal X-ray yesterday. Today his stool is sent for ova, cysts and parasites. What should the laboratory do?

Before a daytime blood examination for microfilariae, a small oral dose of diethylcarbamazine (DEC) is sometimes given. Its purpose is to:

For motile trophozoites of Entamoeba histolytica, a liquid stool should be examined within:

On a thick film, 150 asexual Plasmodium falciparum parasites are counted against 200 white cells. The patient's total WBC count is 6,000/µL. What is the parasite density?

Before Giemsa staining, a thin blood film for malaria parasites is fixed in:

Which preservative keeps helminth eggs and protozoan cysts in stool intact for later concentration?

A febrile patient's first malaria smear is negative. What is the usual advice?

A normal saline wet mount of fresh stool is mainly used to see:

A falciparum malaria patient has 2.5% parasitised red cells on the thin film, and his RBC count is 3.6 million/µL. How many parasitised red cells are there per µL?

For Wuchereria bancrofti microfilariae in India, blood is best collected between:

Zinc sulphate flotation (specific gravity 1.18) recovers cysts well but is poor for:

Before a thick film is reported 'no malaria parasites seen', WHO advises examining at least:

Why is the saline mount of stool examined before the iodine mount?

A liquid stool for amoebic trophozoites cannot be examined for 3 hours. What should be done?

A thick blood film for malaria is spread to the right thickness when:

Why are three stool samples, collected on alternate days, often examined for parasites?

Stool for parasite examination must not be mixed with urine because urine: