HT Quality Control & Assurance 2 — Questions and Answers
Question 1: Which Levey-Jennings rule states that a run is out of control when two consecutive control values exceed the same 2s limit on the same side of the mean?
- 1₃s rule
- 2₂s rule (Correct answer)
- R₄s rule
- 10ₓ rule
Correct answer: 2₂s rule
The 2₂s Westgard rule flags a run when two consecutive controls both exceed +2s or both exceed -2s, indicating systematic error.
Question 2: A histology laboratory notices that hematoxylin staining is progressively weaker over 48 hours despite no reagent changes. What is the most likely cause?
- Oxidation of hematoxylin solution (Correct answer)
- Incorrect water bath temperature
- Contaminated xylene
- Overfixation of tissue
Correct answer: Oxidation of hematoxylin solution
Hematoxylin solutions oxidize over time, reducing their staining capacity, which is why ripened or oxidized solutions must be monitored and replaced.
Question 3: What is the primary purpose of running a negative control in immunohistochemistry?
- Confirm antibody dilution is optimal
- Demonstrate that non-specific background staining is absent (Correct answer)
- Verify antigen retrieval success
- Ensure chromogen development time is correct
Correct answer: Demonstrate that non-specific background staining is absent
A negative control (using a non-immune serum or omitting the primary antibody) confirms that any staining seen in test sections is specific, not background artifact.
Question 4: Which document records the step-by-step procedure for performing a specific staining technique and serves as the foundation for laboratory quality assurance?
- Quality control log
- Standard operating procedure (SOP) (Correct answer)
- Corrective action report
- Proficiency testing summary
Correct answer: Standard operating procedure (SOP)
A Standard Operating Procedure (SOP) provides written, validated instructions ensuring each test is performed consistently and reproducibly.
Question 5: A frozen section stained with Oil Red O shows no lipid droplets, but the pathologist expects lipid. Which control failure is most likely?
- Positive control section lacked lipid
- Negative control was omitted
- Tissue was fixed in formalin before sectioning (Correct answer)
- Counterstain was applied too long
Correct answer: Tissue was fixed in formalin before sectioning
Oil Red O stains neutral lipids in fresh or frozen tissue; formalin fixation and paraffin processing dissolve lipids, preventing staining.
Question 6: According to CAP accreditation requirements, how often must staining controls for routine H&E be run?
- Once per week
- With each new reagent lot only
- With each staining run (Correct answer)
- Once per month
Correct answer: With each staining run
CAP requires that a control tissue section be included with each staining run to verify that reagents and procedure are performing correctly.
Question 7: A microtome blade leaves regularly spaced horizontal lines across every section. What quality issue is this, and what is the corrective action?
- Chatter artifact; tighten tissue clamp and check blade angle
- Knife lines; replace or reposition the blade (Correct answer)
- Compression artifact; adjust section thickness
- Wrinkles; increase water bath temperature
Correct answer: Knife lines; replace or reposition the blade
Regularly spaced parallel lines ('knife lines') are caused by nicks or debris on the blade edge and are corrected by repositioning or replacing the blade.
HT Quality Control & Assurance 2
Which Levey-Jennings rule states that a run is out of control when two consecutive control values exceed the same 2s limit on the same side of the mean?