Positive Control
Definition
A sample of known composition containing the target antigen at a concentration that should produce a defined signal. Run alongside case samples to confirm that the assay reagents and procedure are working correctly. A failed positive control invalidates the entire run.
- Sample Type
- A sample of known positive composition processed in parallel with evidence samples
- Key Function
- Verifies the test system is capable of detecting the target analyte under current conditions
- When Run
- Alongside casework samples in the same test run or batch
Common questions
What is a positive control in forensic testing?+
A positive control is a sample that you know contains the substance or analyte you are testing for. You run it alongside the actual evidence samples to verify that your test method is working correctly. If the positive control fails, the entire batch of results is invalid.
Why do forensic labs use positive controls?+
Positive controls confirm that your testing system can detect the target analyte under the current conditions. Without a positive control passing, you cannot trust that a negative result on an evidence sample actually means the analyte is absent, rather than a broken test.
What happens if a positive control fails?+
A failing positive control means the test run is compromised and must be rejected. All casework results from that run are invalidated and cannot be used. The lab must identify and correct the problem before testing the evidence samples again.
Related terms
- Negative Control
- A sample known not to contain the target antigen. Run alongside case samples to detect contamination or non-specific background reactivity. A reactive...
- Accreditation
- Formal recognition by a standards body (such as UKAS in the UK, A2LA in the US, or NABL in India) that a...
- Certified Reference Material (CRM)
- A sample with one or more analyte concentrations established by an accredited body and traceable to a national metrology institute. NIST SRM...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Epitope Degradation
- The destruction or alteration of the molecular site on an antigen that an antibody recognises, caused by hydrolysis, oxidation, UV radiation, or...
- ISO/IEC 17025
- The international standard for testing and calibration laboratories, published jointly by the International Organization for Standardization and the International Electrotechnical Commission. It...
- Known (K) Sample
- A sample with documented, verified provenance used as the reference in a comparison. The origin of a K sample is not in...
- Limit of Detection (LOD)
- The lowest concentration of analyte that produces a signal reliably distinguishable from the instrument noise, conventionally three times the standard deviation of...
- Limit of Quantitation (LOQ)
- The lowest concentration at which the assay can produce a quantitative measurement with acceptable precision and accuracy, typically defined as the concentration...
- Measurement Traceability
- The property of a measurement result whereby it can be related to a national or international measurement standard through an unbroken chain...
- Negative Control (Blank)
- A sample known to contain no target analyte, processed alongside casework samples. Confirms that background contamination is not producing false signals in...
- OSAC
- Organization of Scientific Area Committees for Forensic Science: established by NIST and DOJ in 2014, it develops consensus forensic standards through structured...
Explained in these topics
- Quality Assurance in Serology LaboratoriesA sample of known positive composition run in parallel with casework samples to verify that the test system is capable of detecting the analyte. A failing posi...
- Reference Standards, Controls and Comparison LogicA sample known to contain the target analyte, processed alongside casework samples. Confirms the method is detecting what it should under current conditions.
- Sensitivity, Specificity, and Quality Controls in Forensic ImmunoassaysA sample of known composition containing the target antigen at a concentration that should produce a defined signal. Run alongside case samples to confirm that...