Overview
Internal, positive, and negative controls are materials or monitoring strategies used with polymerase chain reaction (PCR) amplification to verify detection capability, contamination status, and specimen-level amplification success. Exact designs are assay-specific; interpretation follows the laboratory procedure.
Classification
| Control | Protects against | Failure implication |
|---|---|---|
| Positive | Dead reagents / detection failure | Do not trust the run's patient calls |
| Negative | Contamination / false positives | Investigate before releasing detects |
| Internal (IC) | False negatives from failed amplification | Failed IC ≠ safe negative |
Morphologic Features
Not applicable, this entry covers quality controls, not morphologic identification.
Laboratory Characteristics
- Positive/negative controls are often batch-level; IC is often specimen-level
- Passing batch controls do not rescue a failed specimen IC
- Names and expected patterns vary by assay, use the SOP
Reference Intervals
Not a numeric reference interval. Control pass/fail criteria are defined by each validated assay and laboratory SOP.
Clinical and Laboratory Significance
Controls determine whether a PCR result can be trusted. A not-detected call without a valid IC (when required) risks reporting a false negative and misleading care.
Differential Considerations
Flat target curve + failed IC → invalid/amplification problem until proven otherwise, not true target absence. Flat target curve + passing IC → supports not detected per assay rules.
Comparison Tables
Amplification control checkpoints
| Situation | Safe action | Unsafe action |
|---|---|---|
| IC fails; no target signal | Invalid/retest per SOP | Report not detected |
| Positive control fails | Hold run; follow SOP | Release patient results |
| Negative control shows target | Contamination pathway per SOP | Ignore and release detects |
Classification Frameworks
Not applicable . World Health Organization (WHO) disease classifications do not define PCR amplification control rules.
Laboratory Notes
- Positive → can detect; Negative → contamination check; IC → this specimen amplified
- Failed IC ≠ safe negative
- Interpretation follows the validated assay and laboratory SOP
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.
Frequently Asked Questions
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