A 46-year-old woman was admitted 6 days ago for a femur fracture and is receiving cefazolin. Today she has had four watery stools, and she has had no laxatives in the past 48 hours. She is HIV negative, her neutrophil count is 5.2 x 10^3/µL [5.2 x 10^9/L], and there is no diarrhea outbreak on the ward. One liquid stool arrives with three orders: bacterial culture for Salmonella, Shigella, Campylobacter and Shiga toxin-producing E. coli; an ova and parasite examination; and a C. difficile NAAT. The laboratory applies the 3-day rule for hospital-onset diarrhea. Which test or tests should be performed?

Bacterial culture and C. difficile NAAT

Ova and parasites and C. difficile NAAT

Which specimen is acceptable for anaerobic culture?

Expectorated first-morning sputum

A bone biopsy taken in surgery for culture arrives in an unlabeled sterile container with a complete requisition. The best action is to:

Have the surgical team identify and label it, then document

Reject it and ask for a repeat biopsy

Label it from the requisition and process it

Process it now and label it when results are ready

Only 0.5 mL of CSF arrives with orders for bacterial, fungal and mycobacterial culture and HSV PCR. The best action is to:

Ask the physician which tests matter most

Do the tests in the order listed until it runs out

Reject it as an insufficient volume

Split it equally between the four tests

Specimen processing: prioritization and rejection

7 ASCP MLS practice questions on Specimen processing: prioritization and rejection, part of Microbiology. The first 7 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 46-year-old woman was admitted 6 days ago for a femur fracture and is receiving cefazolin. Today she has had four watery stools, and she has had no laxatives in the past 48 hours. She is HIV negative, her neutrophil count is 5.2 x 10^3/µL [5.2 x 10^9/L], and there is no diarrhea outbreak on the ward. One liquid stool arrives with three orders: bacterial culture for Salmonella, Shigella, Campylobacter and Shiga toxin-producing E. coli; an ova and parasite examination; and a C. difficile NAAT. The laboratory applies the 3-day rule for hospital-onset diarrhea. Which test or tests should be performed?
1. AC. difficile NAAT only
2. BBacterial culture and C. difficile NAAT
3. CAll three tests as ordered
4. DOva and parasites and C. difficile NAAT
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Answer: A · C. difficile NAAT only
Diarrhea that starts more than 3 days after admission is rarely caused by enteric bacterial pathogens or intestinal parasites, which are acquired in the community. The usual cause of hospital-onset diarrhea, especially in a patient on antibiotics, is C. difficile, and this stool meets its testing criteria: three or more unformed stools in 24 hours and no recent laxatives. The exceptions to the rule, such as HIV infection, neutropenia, age 65 or older with serious illness, or a suspected outbreak, do not apply here. The laboratory performs the C. difficile test and contacts the physician to cancel the culture and O&P, documenting the reason.
- B: Bacterial culture is rejected under the 3-day rule when no exception applies.
- C: Culture and O&P have very low yield in hospital-onset diarrhea and are rejected under the rule.
- D: An O&P examination is rejected under the 3-day rule when no exception applies.
Question 2 · Medium
Which specimen is acceptable for anaerobic culture?
1. ASwab of the vaginal wall
2. BNeedle-aspirated pleural fluid
3. CExpectorated first-morning sputum
4. DClean-catch midstream urine
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Answer: B · Needle-aspirated pleural fluid
Anaerobes are part of the normal flora of the mouth, gut, vagina and skin. Specimens that pass through these sites always contain anaerobes, so culturing them gives misleading results. Acceptable specimens come from normally sterile sites, collected by needle aspiration or tissue biopsy, and are sent in an anaerobic transport container. Sputum, voided urine and vaginal swabs are rejected for anaerobic culture.
- A: The vagina normally contains many anaerobes.
- C: Sputum is contaminated with oral anaerobes.
- D: Voided urine picks up urethral and perineal flora.
Question 3 · Hard
A bone biopsy taken in surgery for culture arrives in an unlabeled sterile container with a complete requisition. The best action is to:
1. AReject it and ask for a repeat biopsy
2. BLabel it from the requisition and process it
3. CProcess it now and label it when results are ready
4. DHave the surgical team identify and label it, then document
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Answer: D · Have the surgical team identify and label it, then document
A surgical biopsy cannot be collected again without another procedure, so it is not simply discarded. Laboratory staff must not label it themselves from the requisition, because they cannot confirm whose specimen it is. The person responsible for the collection comes to identify and label it and signs for that, and the event is documented, often with a comment on the report. Easily recollected specimens such as urine are simply recollected instead.
- A: Repeating surgery for a labeling error causes avoidable harm.
- B: Staff cannot confirm identity by matching a container to a form.
- C: Processing an unidentified specimen risks reporting to the wrong patient.
Question 4 · Easy
Which specimen should be rejected for routine bacterial culture?
1. ABronchoalveolar lavage fluid
2. BIntravascular catheter tip
3. CSuprapubic urine aspirate
4. DFoley catheter tip
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Answer: D · Foley catheter tip
A Foley catheter tip passes through the urethra and is always coated with urethral and perineal flora, so its culture cannot show which organism causes infection. Laboratories reject it and ask for urine aspirated from the catheter port instead. Intravascular catheter tips can be cultured semi-quantitatively when catheter-related bloodstream infection is suspected, together with blood cultures. Suprapubic aspirates and BAL fluid are acceptable specimens.
- A: BAL fluid is accepted, often for quantitative culture.
- B: Intravascular tips are accepted for semi-quantitative (roll-plate) culture.
- C: A suprapubic aspirate is the cleanest urine specimen available.
Question 5 · Hard
Only 0.5 mL of CSF arrives with orders for bacterial, fungal and mycobacterial culture and HSV PCR. The best action is to:
1. AAsk the physician which tests matter most
2. BDo the tests in the order listed until it runs out
3. CReject it as an insufficient volume
4. DSplit it equally between the four tests
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Answer: A · Ask the physician which tests matter most
CSF cannot easily be collected again, so it is not rejected for low volume. Splitting a small volume four ways leaves too little for any test to be sensitive, because fungal and mycobacterial cultures need several milliliters. The laboratory calls the physician, who ranks the tests from the clinical picture, and documents the decision. In suspected acute bacterial meningitis, the Gram stain and bacterial culture usually come first.
- B: The order on the request does not reflect clinical priority.
- C: Irreplaceable specimens such as CSF are not rejected for low volume.
- D: Dividing it leaves too little for any test to be sensitive.
Question 6 · Hard
A midstream urine collected at 07:00 was left at room temperature on the ward. It reaches the laboratory at 14:00 in a plain cup with an order for culture. The best action is to:
1. ARequest a new specimen and record why
2. BCulture it and report only gram-negative rods
3. CCulture it and report counts as usual
4. DRefrigerate it and culture it tomorrow
Answer and explanation in LearnFree account
Question 7 · Medium
Four specimens reach the microbiology bench at the same time. The one to process first is:
1. ACSF from a febrile 2-month-old
2. BRefrigerated urine for routine culture
3. CNasal swab for MRSA screening
4. DStool in Cary-Blair for enteric culture
Answer and explanation in LearnFree account

Specimen processing: prioritization and rejection

Which specimen is acceptable for anaerobic culture?

A bone biopsy taken in surgery for culture arrives in an unlabeled sterile container with a complete requisition. The best action is to:

Which specimen should be rejected for routine bacterial culture?

Only 0.5 mL of CSF arrives with orders for bacterial, fungal and mycobacterial culture and HSV PCR. The best action is to:

A midstream urine collected at 07:00 was left at room temperature on the ward. It reaches the laboratory at 14:00 in a plain cup with an order for culture. The best action is to:

Four specimens reach the microbiology bench at the same time. The one to process first is: