Internal Positive Control (IPC)
Definition
An exogenous DNA template of known sequence and concentration added to the PCR reaction alongside the forensic sample. If the IPC fails to amplify, PCR inhibition is suspected. If it amplifies normally but the target does not, the sample is likely DNA-negative rather than inhibited.
- Field
- Forensic PCR-based DNA testing
- Nature
- Exogenous DNA template of known sequence/concentration
- Purpose
- Detects PCR inhibition
- Failure interpretation
- IPC fails: inhibition suspected
- Success but no target
- Sample likely DNA-negative
Common questions
How does an analyst tell the difference between PCR inhibition and a genuinely DNA-negative sample?+
If the internal positive control amplifies normally alongside the forensic target, the reaction chemistry worked, so a missing target result means the sample likely lacked amplifiable DNA. If the IPC itself fails to amplify, the reaction was compromised, pointing to an inhibitor rather than an absence of DNA.
What substances commonly cause the PCR inhibition an IPC is designed to catch?+
Humic acid from soil, indigo dye from denim, haem compounds from blood, and certain textile dyes are among the common environmental and biological inhibitors that can suppress amplification and would be flagged by IPC failure.
Related terms
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- PCR Inhibitor
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