A 3-year-old girl lives with her grandfather, who has smear-positive cavitary tuberculosis. She has a chronic cough and weight loss but cannot produce sputum. Early-morning gastric aspirates are collected by nasogastric tube on three consecutive days, before she eats. The day 1 and day 3 aspirates are neutralized with sodium carbonate at the bedside and reach the laboratory within 1 hour. The day 2 aspirate is collected into a plain sterile tube, left at room temperature on the ward, and arrives 7 hours later without neutralization. All three are processed the same way. Mycobacterial cultures: day 1 and day 3 grow M. tuberculosis complex; day 2 shows no growth of any organism at 6 weeks. The most likely reason the day 2 culture is negative is:

Gastric acid killed the bacilli during the delay

Decontamination was too harsh for this specimen

Too few bacilli were swallowed that night

Contaminating flora overgrew the mycobacteria

A stool for culture of Salmonella, Shigella and Campylobacter will reach the laboratory the next day. It should be placed in:

Polyvinyl alcohol (PVA) fixative

A urine for culture cannot be plated within 2 hours of collection, and no preservative tube is available. How should it be held?

At room temperature (20-25 °C)

A swab arrives with two patient identifiers on its label but no specimen source. Why must the laboratory confirm the source before processing?

It decides the media and which growth is significant

It serves as one of the two patient identifiers

It is needed only for infection-control records

It decides which Gram stain reagents are used

Specimen collection and transport

16 ASCP MLS practice questions on Specimen collection and transport, part of Microbiology. The first 16 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 3-year-old girl lives with her grandfather, who has smear-positive cavitary tuberculosis. She has a chronic cough and weight loss but cannot produce sputum. Early-morning gastric aspirates are collected by nasogastric tube on three consecutive days, before she eats. The day 1 and day 3 aspirates are neutralized with sodium carbonate at the bedside and reach the laboratory within 1 hour. The day 2 aspirate is collected into a plain sterile tube, left at room temperature on the ward, and arrives 7 hours later without neutralization. All three are processed the same way. Mycobacterial cultures: day 1 and day 3 grow M. tuberculosis complex; day 2 shows no growth of any organism at 6 weeks. The most likely reason the day 2 culture is negative is:
1. ADecontamination was too harsh for this specimen
2. BToo few bacilli were swallowed that night
3. CGastric acid killed the bacilli during the delay
4. DContaminating flora overgrew the mycobacteria
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Answer: C · Gastric acid killed the bacilli during the delay
Young children swallow their respiratory secretions, so fasting early-morning gastric aspirates are used when sputum cannot be produced. Gastric acid kills mycobacteria, so the aspirate must be neutralized with sodium carbonate or processed promptly after collection. The day 2 specimen sat unneutralized for 7 hours, and a culture with no growth at all fits loss of viable bacilli; overgrowth would have given a contaminated culture instead. The other two aspirates grew with the same processing, so the decontamination step and the number of bacilli are unlikely causes. The day 2 result should be noted as compromised, and another neutralized aspirate collected if needed.
- A: All three aspirates had the same decontamination, and two grew M. tuberculosis.
- B: The other two aspirates grew readily, and the handling error is the better explanation.
- D: Overgrowth gives a contaminated culture, but this one grew nothing at all.
Question 2 · Easy
A stool for culture of Salmonella, Shigella and Campylobacter will reach the laboratory the next day. It should be placed in:
1. AViral transport medium
2. BCary-Blair transport medium
3. CPolyvinyl alcohol (PVA) fixative
4. D10% formalin
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Answer: B · Cary-Blair transport medium
Cary-Blair is a buffered, low-nutrient semisolid medium that keeps enteric bacteria alive without letting them multiply. Its high pH protects acid-sensitive organisms such as Shigella. Formalin and PVA are fixatives for ova and parasite examination and kill bacteria. Viral transport medium contains antibiotics that would inhibit bacterial pathogens.
- A: Viral transport medium contains antibiotics that inhibit bacteria.
- C: PVA fixes parasites for permanent stains and kills bacteria.
- D: Formalin kills bacteria; it preserves parasites for microscopy.
Question 3 · Easy
A urine for culture cannot be plated within 2 hours of collection, and no preservative tube is available. How should it be held?
1. AFrozen at -20 °C
2. BAt room temperature (20-25 °C)
3. CIn a 35 °C incubator
4. DRefrigerated at 2-8 °C
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Answer: D · Refrigerated at 2-8 °C
Urine is a good growth medium, so bacteria in an unrefrigerated specimen keep multiplying and the colony count rises falsely. Refrigeration at 2-8 °C holds the count steady for up to 24 hours. A boric acid preservative tube is the alternative when refrigeration is not possible. A specimen left unrefrigerated for more than 2 hours should be recollected.
- A: Freezing can kill some bacteria and is not used for urine culture.
- B: Bacteria multiply at room temperature and inflate the colony count.
- C: Incubation speeds growth and makes the count meaningless.
Question 4 · Medium
A swab arrives with two patient identifiers on its label but no specimen source. Why must the laboratory confirm the source before processing?
1. AIt serves as one of the two patient identifiers
2. BIt is needed only for infection-control records
3. CIt decides the media and which growth is significant
4. DIt decides which Gram stain reagents are used
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Answer: C · It decides the media and which growth is significant
Media, incubation conditions and the meaning of growth all depend on where the specimen came from. A throat swab is screened for beta-hemolytic streptococci, while a deep wound may need aerobic and anaerobic culture, and normal flora means different things at each site. The specimen is held while the source is confirmed with the collector, and the call is documented. The source is not a patient identifier.
- A: Identifiers are patient details such as name and date of birth, not the source.
- B: The source mainly guides processing and reporting, not just records.
- D: The Gram stain uses the same reagents for every specimen.
Question 5 · Easy
When its processing must wait, CSF for bacterial culture should be held at:
1. ARoom temperature
2. B-20 °C (frozen)
3. C2-8 °C (refrigerated)
4. DOn ice packs in a cooler
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Answer: A · Room temperature
The main bacterial causes of meningitis, Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae, are fragile and die when chilled. CSF for bacterial culture is therefore carried to the laboratory at once and kept at room temperature, never refrigerated. It is a STAT specimen and is processed as soon as it arrives. A separate portion for viral PCR may be refrigerated.
- B: Freezing kills bacteria and makes culture unreliable.
- C: Refrigeration kills cold-sensitive meningitis agents such as N. meningitidis.
- D: Ice packs chill the specimen just as a refrigerator does.
Question 6 · Medium
A nasopharyngeal swab in viral transport medium must wait 7 days for testing, beyond the assay's 72-hour limit for refrigerated storage. How should it be stored?
1. ARefrigerated at 2-8 °C until tested
2. BAt room temperature
3. CFrozen at -70 °C or colder
4. DFrozen at -20 °C
Answer and explanation in LearnFree account
Question 7 · Easy
The patient label on a sterile urine culture container should be placed on:
1. AThe lid, where it is easy to see
2. BThe container, not the lid
3. CThe outer specimen bag only
4. DThe requisition form only
Answer and explanation in LearnFree account
Question 8 · Hard
A rural clinic collects four specimens at 18:00, and the courier arrives at 07:00 the next day. The specimen that should be refrigerated overnight is the:
1. ACSF for bacterial culture
2. BSputum for mycobacterial culture
3. CAbscess aspirate in an anaerobic vial
4. DUrethral swab for gonococcal culture
Answer and explanation in LearnFree account
Question 9 · Medium
Stool for Shigella culture must be plated quickly or placed in Cary-Blair medium mainly because Shigella:
1. AIs killed by acid from other stool flora
2. BNeeds 42 °C, as Campylobacter does
3. CIs killed by refrigeration at 2-8 °C
4. DIs a strict anaerobe that dies in room air
Answer and explanation in LearnFree account
Question 10 · Hard
An endocervical swab for Neisseria gonorrhoeae culture was collected on a synthetic swab in Amies medium, refrigerated overnight, then plated on modified Thayer-Martin agar and incubated at 35 °C in 5% CO2. The culture is negative, but a NAAT on a second swab is positive. The most likely cause is:
1. AIncubation in 5% CO2
2. BRefrigeration of the swab overnight
3. CUse of a synthetic-tipped swab
4. DChoice of modified Thayer-Martin agar
Answer and explanation in LearnFree account
Question 11 · Hard
A surface swab of a chronic diabetic foot ulcer grows four organisms, including coagulase-negative staphylococci and diphtheroids. Which specimen should be requested to find the true pathogen?
1. AA repeat surface swab the next day
2. BA swab of the intact skin around the ulcer
3. CTissue from the ulcer base after debridement
4. DA swab of the drainage on the dressing
Answer and explanation in LearnFree account
Question 12 · Easy
How should skin scrapings for dermatophyte culture be sent to the laboratory?
1. ADry, in a clean paper envelope
2. BIn viral transport medium
3. CIn sterile saline, refrigerated
4. DIn 10% KOH solution
Answer and explanation in LearnFree account
Question 13 · Hard
A watery stool for ova and parasites was collected without preservative at 08:00 and reached the laboratory at 12:00. Which parasite stage is most likely to have been lost?
1. ATapeworm segments (proglottids)
2. BHelminth eggs
3. CProtozoan trophozoites
4. DProtozoan cysts
Answer and explanation in LearnFree account
Question 14 · Easy
Without refrigeration or a holding medium, most specimens for routine bacterial culture should reach the laboratory within:
1. A8 hours of collection
2. B2 hours of collection
3. C48 hours of collection
4. D24 hours of collection
Answer and explanation in LearnFree account
Question 15 · Medium
A patient has had an indwelling urinary catheter for 3 days. How should urine for culture be collected?
1. APour it from the drainage bag
2. BAspirate it from the disinfected sampling port
3. CRemove the catheter and send its tip
4. DDisconnect the tubing and catch the drip
Answer and explanation in LearnFree account
Question 16 · Medium
What is the best way to collect and send a specimen for culture of a suspected anaerobic infection?
1. AAn aspirate or tissue in an anaerobic transport container
2. BA midstream urine sample
3. CA dry swab kept at room temperature for 24 hours
4. DA refrigerated expectorated sputum
Answer and explanation in LearnFree account

Specimen collection and transport

A stool for culture of Salmonella, Shigella and Campylobacter will reach the laboratory the next day. It should be placed in:

A urine for culture cannot be plated within 2 hours of collection, and no preservative tube is available. How should it be held?

A swab arrives with two patient identifiers on its label but no specimen source. Why must the laboratory confirm the source before processing?

When its processing must wait, CSF for bacterial culture should be held at:

A nasopharyngeal swab in viral transport medium must wait 7 days for testing, beyond the assay's 72-hour limit for refrigerated storage. How should it be stored?

The patient label on a sterile urine culture container should be placed on:

A rural clinic collects four specimens at 18:00, and the courier arrives at 07:00 the next day. The specimen that should be refrigerated overnight is the:

Stool for Shigella culture must be plated quickly or placed in Cary-Blair medium mainly because Shigella:

An endocervical swab for Neisseria gonorrhoeae culture was collected on a synthetic swab in Amies medium, refrigerated overnight, then plated on modified Thayer-Martin agar and incubated at 35 °C in 5% CO2. The culture is negative, but a NAAT on a second swab is positive. The most likely cause is:

A surface swab of a chronic diabetic foot ulcer grows four organisms, including coagulase-negative staphylococci and diphtheroids. Which specimen should be requested to find the true pathogen?

How should skin scrapings for dermatophyte culture be sent to the laboratory?

A watery stool for ova and parasites was collected without preservative at 08:00 and reached the laboratory at 12:00. Which parasite stage is most likely to have been lost?

Without refrigeration or a holding medium, most specimens for routine bacterial culture should reach the laboratory within:

A patient has had an indwelling urinary catheter for 3 days. How should urine for culture be collected?

What is the best way to collect and send a specimen for culture of a suspected anaerobic infection?