Overview
Common PCR failures are recurring invalid or unreliable amplification outcomes recognized by curve and control patterns. Safe handling starts with pattern recognition and SOP-directed holds, not forced clinical calls.
Classification
| Pattern | First safe stance |
|---|---|
| No amplification | Verify IC and run controls before not-detected |
| Failed controls | Hold; scope specimen vs run failure |
| Unexpected positives | Review negatives/NTC; contamination awareness |
| Late curves | Apply assay rules; avoid severity myths |
Morphologic Features
Not applicable, failure patterns are instrument/control findings, not morphologic diagnoses.
Laboratory Characteristics
- Tag exceptions by pattern before choosing SOP branch
- Separate specimen-level from batch-level problems
- Document repeats and outcomes
Reference Intervals
Not applicable, acceptance uses assay control criteria, not patient reference intervals. Ct/Cq cutoffs are not universal.
Clinical and Laboratory Significance
Mis-handled failure patterns produce false-negative or false-positive reports. Correct pattern recognition protects release decisions.
Differential Considerations
Laboratory differential spans true target absence, inhibition, contamination, reagent/setup error, and assay-specific late calls, resolve with controls and SOP.
Comparison Tables
Failure pattern guardrails
| Pattern | Unsafe framing | Safe framing |
|---|---|---|
| Quiet target, failed IC | Negative | Invalid / inhibited |
| Late rise | Mild disease | Assay-specific interpretation |
| Odd positives + failed NTC | Release the strong ones | Hold; contamination pathway |
Classification Frameworks
Not applicable.
Laboratory Notes
- Distinguish no amplification, inhibited amplification, late amplification, and valid control performance
- Never invent negatives to clear an exception list
- Interpretation must follow the validated assay and laboratory procedure
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021. (Molecular diagnostics chapters, verify current edition.)
- Buckingham L. Molecular Diagnostics: Fundamentals, Methods, and Clinical Applications. 3rd ed. F.A. Davis; 2019. (Verify current edition.)
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute (CLSI). Consult current CLSI molecular method documents available through your laboratory, document numbers and editions change; do not treat any single CLSI title as universal.
- Institutional molecular laboratory SOPs, assay manufacturer instructions for use (IFU), and locally adopted accreditation requirements. Always verify current local practice.
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