Overview
Molecular controls are materials of known content run alongside patient specimens to verify that each stage of testing performed as expected, so that a detected or not-detected result can be trusted.
Classification
| Control type | Protects against |
|---|---|
| Positive control | Reagent or detection chemistry failure |
| Negative control / no-template control | Contamination or carryover |
| Internal control | Inhibition or extraction failure (false negatives) |
| Extraction control | Extraction process failure, nucleic acid loss |
Morphologic Features
Not applicable, controls are quality-monitoring materials, not morphologic entities.
Laboratory Characteristics
- Reviewed before every result release, on every run and every specimen
- Some controls apply per run (positive, negative); others apply per specimen (internal, extraction)
- Exact requirements and combined control designs vary by assay and platform, verify institutional SOP
Reference Intervals
Not applicable in the traditional sense, controls have expected qualitative or quantitative performance defined by assay validation, not patient reference intervals.
Clinical and Laboratory Significance
Controls determine whether a patient result can be interpreted at all. Without passing the controls tied to a given result, no diagnostic conclusion can be drawn from it.
Differential Considerations
Not applicable, an unexpected control result should prompt troubleshooting (reagent, contamination, inhibition, extraction) rather than a clinical differential diagnosis.
Comparison Tables
Interpretation guardrails for control failures
| Situation | Safe framing | Unsafe framing |
|---|---|---|
| Internal control fails, no signal | Invalid, repeat/recollect | Negative |
| One specimen's control fails in a passing batch | That specimen alone is invalid | Whole batch covers it, report as is |
| Positive control fails | Hold entire run | Release unaffected-looking results anyway |
Classification Frameworks
Not applicable.
Laboratory Notes
- Document every control failure and the resulting action per institutional SOP
- Never let passing controls elsewhere in a batch substitute for a specimen's own required control
- Escalate repeated or unexplained control failures per institutional troubleshooting 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.
Frequently Asked Questions
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