Inhibition Index
Definition
A quantitative measure of PCR inhibitor burden in a DNA extract, derived from the Ct shift of an internal positive control (IPC) in a human-specific qPCR assay. A depressed IPC Ct indicates inhibitor presence requiring dilution or re-extraction.
- DNA inhibitor detection method
- Internal positive control (IPC) Ct shift in human-specific qPCR
- Blood-typing application
- Titre difference between control antiserum and test antiserum after stain incubation
- Secretor status convention
- Two or more serial dilution drop = evidence of blood-group substance
Common questions
What does inhibition index measure in DNA testing?+
In DNA extraction, the inhibition index is a number that shows how much PCR inhibitor (unwanted substance) is in your DNA sample. It's calculated by looking at how much the internal positive control's Ct value shifts during qPCR testing. A bigger shift means more inhibitor is present.
Why does inhibition index matter for blood typing?+
In blood-group typing, inhibition index measures how much the antiserum titre drops after the stain extract is added. A larger drop shows that antigens from the sample successfully neutralized the antibodies, which helps confirm what blood-group substance is present.
What titre drop is considered significant for secretor status?+
For secretor status determination, a drop of two or more serial dilutions in anti-A, anti-B, or anti-H antiserum is conventionally accepted as evidence that the corresponding blood-group substance is present in the body fluid.
Related terms
- Absorption
- The purification technique in which a crude antiserum is mixed with antigen preparations from cross-reacting species. Cross-reactive antibodies bind those antigens and...
- Blood-Group Substance
- Soluble ABO antigens (A substance, B substance, H substance) present in the body fluids of secretors. Chemically distinct from the glycolipid-bound cell-surface...
- Chaotropic Salt
- Guanidinium thiocyanate or hydrochloride at 4-6 M concentration. Disrupts the hydration shell of DNA and causes it to bind electrostatically to silica...
- Chelex-100
- Styrene-divinylbenzene ion-exchange resin with iminodiacetate chelating groups. Used at 5% w/v in forensic DNA extraction to bind divalent metal cations during boiling...
- Elution
- The release of antibody from antigen, typically by heating to 56-70 degrees Celsius. In the absorption-elution method, this step liberates the antibody...
- FUT2 Gene
- The Fucosyltransferase 2 gene on chromosome 19q13, encoding the alpha-1,2-fucosyltransferase enzyme responsible for adding fucose to type-1 chain precursors in secretory tissues...
- Indicator Cells
- Commercially prepared or freshly washed red cells of known ABO group used to detect antibody activity in an eluate or residual antiserum....
- Maxwell RSC 48
- Promega cartridge-based magnetic-bead extraction instrument. Each cartridge is pre-loaded with all reagents; closed-format processing eliminates cross-contamination. Used at FBI Laboratory and AFMES.
- Mixed Agglutination
- A microscopy-based technique in which indicator cells form rosette aggregates around antigen-bearing stain material via antibody bridges. Positive results are read as...
- Non-Secretor
- An individual homozygous for non-functional FUT2 alleles who produces no H, A, or B antigen in saliva, semen, or other exocrine secretions,...
- Phenol-Chloroform-Isoamyl Alcohol (PCI) Extraction
- Organic extraction method using differential solubility to partition DNA into an aqueous phase while proteins and lipids accumulate at the organic-aqueous interface...
- QIAcube Connect
- QIAGEN robotic workstation that automates spin-column extraction protocols (QIAamp DNA Investigator). Processes 12 samples per 60-minute run; used in UK, US and...
Explained in these topics
- ABO Typing on Stains: Absorption-Elution and InhibitionIn absorption-inhibition, the numerical difference in titre between a control antiserum (no stain extract added) and the test antiserum after incubation with s...
- DNA Extraction: Organic, Chelex, Silica-Column and Magnetic-BeadA quantitative measure of PCR inhibitor burden in a DNA extract, derived from the Ct shift of an internal positive control (IPC) in a human-specific qPCR assay...
- Secretor Status and Its Forensic ValueThe titre drop in anti-A, anti-B, or anti-H antiserum after incubation with a body-fluid extract. A drop of two or more serial dilutions is conventionally take...