A real-time PCR assay for influenza includes an exogenous internal amplification control spiked into every sample. A patient sample shows no amplification of either the target gene or the internal control. The correct interpretation is:
- A Sample is truly negative for influenza
- B Sample is positive for influenza with target overload suppressing the control
- C PCR inhibition or extraction failure, result invalid and must be repeated ✓
- D Assay contamination occurred and all results should be discarded
Correct answer: C. PCR inhibition or extraction failure, result invalid and must be repeated
Explanation
The internal amplification control verifies both extraction efficiency and absence of inhibitors such as mucus, blood, or heme. If the control fails to amplify alongside a negative target, the run for that specimen is invalid because a false negative from inhibition cannot be excluded. A true negative requires successful amplification of the control. Contamination would produce false positives, not failure of every signal in one well.
Reference: Koneman's Color Atlas and Textbook of Diagnostic Microbiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.