Histopathology quality control and safety

5 DOH Abu Dhabi (HAAD) lab licensing practice questions on Histopathology quality control and safety, part of Histopathology and Cytology. The first 5 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   Used xylene from a tissue processor or stainer should be:

   1. APoured down the sink with plenty of running water
   2. BMixed with the formalin waste in the same drum
   3. CNeutralized with sodium bicarbonate, then discarded
   4. DKept as hazardous waste or recycled by distillation

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   Answer: D · Kept as hazardous waste or recycled by distillation

   Xylene is flammable and toxic, so it must never go down the drain. It is collected in labeled, closed solvent waste containers for a licensed hazardous waste contractor, or recycled on site in a solvent distiller. Distilled xylene is checked for water and purity before reuse. Different waste streams, such as formalin and solvents, are kept separate.

   • A: Flammable solvents must never be poured into drains.
   • B: Waste streams are kept separate; mixing them complicates safe disposal.
   • C: Xylene is not an acid, and bicarbonate does not make it safe.

2. Question 2 · Medium

   In a Ziehl-Neelsen run, the positive control section shows red acid-fast bacilli, but a patient's lung section shows none. How should this be read?

   1. AThe patient section must be restained with a Gram stain
   2. BThe method worked; no bacilli were found in that section
   3. CThe run failed and must be repeated before reporting
   4. DThe control is invalid because it came from a different block

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   Answer: B · The method worked; no bacilli were found in that section

   A positive control containing acid-fast bacilli, stained in the same run, shows that the reagents and timings could demonstrate the organisms. The patient section can then be reported as no acid-fast bacilli seen, which does not rule out infection, because organisms may be sparse. Controls should be fixed and processed like patient tissue. Culture and molecular tests are more sensitive than tissue stains.

   • A: Mycobacteria stain poorly with Gram methods.
   • C: A run fails only when the control does not stain as expected.
   • D: Controls always come from a separate block known to be positive.

3. Question 3 · Hard

   Personal air monitoring of a grossing technologist shows an 8-hour time-weighted average of 0.6 ppm formaldehyde. Under the US OSHA formaldehyde standard, the action level is 0.5 ppm and the permissible exposure limit is 0.75 ppm (8-hour TWA). Which conclusion is correct?

   1. AAbove the action level: keep monitoring and improve controls
   2. BAbove the exposure limit: respirators are required at once
   3. CAbove the short-term limit: grossing must stop today
   4. DBelow the action level: monitoring can now stop

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   Answer: A · Above the action level: keep monitoring and improve controls

   0.6 ppm is above the 0.5 ppm action level but below the 0.75 ppm limit. Under the OSHA standard, exposure at or above the action level requires periodic monitoring, at least every 6 months, and medical surveillance, and the laboratory should look for ways to lower exposure, such as better ventilation. Respirators become required when exposure exceeds the limit and engineering controls cannot bring it down. The short-term limit (2 ppm over 15 minutes) is judged from separate short samples, not from the 8-hour average.

   • B: 0.6 ppm is below the 0.75 ppm limit, so respirators are not yet required.
   • C: The short-term limit applies to 15-minute samples, which were not taken here.
   • D: 0.6 ppm is above the action level, so monitoring must continue.

4. Question 4 · Easy

   Where should specimens in formalin be opened and grossed?

   1. AA class II biosafety cabinet that recirculates air
   2. BA grossing station with downdraft or local exhaust
   3. CAn open bench beside an opened window
   4. DA cold room, to lower formalin evaporation

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   Answer: B · A grossing station with downdraft or local exhaust

   Grossing stations draw vapor down and away from the breathing zone into ducted exhaust. Biosafety cabinets that recirculate air through HEPA filters protect against particles, not chemical vapors. Containers are kept closed when not in use, and staff wear gloves, eye protection and a fluid-resistant gown. Exposure is checked by air monitoring.

   • A: HEPA filters do not remove formaldehyde vapor, so recirculated air returns it to the room.
   • C: A window gives uncontrolled airflow and no capture at the source.
   • D: Cold slows evaporation a little but does not remove vapor from the breathing zone.

5. Question 5 · Medium

   A 1 L bottle of 10% formalin breaks on the floor of the grossing room. Which response is most appropriate?

   1. ALeave the room closed until the formalin evaporates overnight
   2. BCover it with paper towels and leave it for cleaning staff
   3. CWear gloves and goggles, ventilate, and use a formalin spill kit
   4. DMop it up at once with water and paper towels, without gloves

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   Answer: C · Wear gloves and goggles, ventilate, and use a formalin spill kit

   Spilled formalin releases formaldehyde vapor, which irritates the eyes and airways and is a carcinogen. Staff should increase ventilation, keep others out, and put on nitrile gloves, goggles and, for large spills, a suitable respirator. A formaldehyde neutralizing or absorbent spill kit is used, glass is picked up with tools, and the waste goes into a sealed, labeled container. The spill is reported and recorded under the laboratory's safety program.

   • A: Letting it evaporate fills the room with formaldehyde vapor.
   • B: Untrained cleaning staff should not be left to deal with a chemical spill.
   • D: Bare-handed mopping with water spreads vapor and exposes the skin.