Confirmatory Test
Definition
A test with sufficient specificity to establish the identity of a biological fluid for reporting purposes. Examples include Takayama and Teichmann crystal tests for blood, prostate-specific antigen (PSA) assay for semen, and microscopic identification of spermatozoa.
- Key difference
- Much higher specificity than presumptive tests. Identifies the exact analyte, not just its possible presence.
- Methods
- Chromatographic-mass-spectrometric (GC-MS, LC-MS-MS) for drugs. Crystal tests or immunochromatographic strips for blood and body fluids.
- Court defensibility
- Confirmatory results are defensible evidence. Presumptive results alone are not.
Common questions
What's the difference between a presumptive test and a confirmatory test?+
A presumptive test flags that something might be present, like a stain resembling blood. A confirmatory test proves what it actually is using specific methods like chromatography or immunochromatographic strips. Confirmatory tests are what you report in court.
What methods count as confirmatory for drugs and body fluids?+
For drugs, GC-MS or LC-MS-MS pinpoint the exact substance. For blood, tests like the Takayama crystal test, the Teichmann test, or immunochromatographic strips targeting species-specific proteins such as glycophorin A confirm it. For other body fluids, immunochromatographic strips target fluid-specific proteins. All are defensible in court.
Why not just use a presumptive test?+
Presumptive tests are sensitive but can give false positives. Confirmatory tests are much more specific and eliminate false positives before evidence is reported. This specificity is what makes the result stand up in court.
Related terms
- Presumptive Test
- A fast, low-cost, class-specific screen used to triage a caseload before instrumental work begins. Examples are Marquis reagent for opioids and amphetamines,...
- Luminol
- A chemiluminescent reagent (5-amino-2,3-dihydro-1,4-phthalazinedione) that produces blue-white light on contact with haemoglobin-derived iron. Detects blood diluted to 1:10,000,000 or more. Used as...
- ABAcard P30
- A lateral-flow immunochromatographic strip manufactured by Abacus Diagnostics and validated by the Scientific Working Group for DNA Analysis Methods (SWGDAM) for forensic...
- Acid Phosphatase (AP)
- An enzyme present at high concentrations in seminal plasma. The Brentamine Fast Violet B (or SERI AP) spray test detects acid phosphatase...
- Adulteration
- Deliberate tampering of a urine specimen to defeat the screen. Common adulterants include nitrite, chromate, peroxide, glutaraldehyde, niacin, vinegar and Visine. Detected...
- Amylase
- An enzyme that breaks down starch and is present at high activity in saliva. The Phadebas press test and starch-iodine method detect...
- Benzidine Test
- Historical presumptive test using benzidine and hydrogen peroxide to give a blue colour. Banned for routine use because benzidine is a confirmed...
- BPA
- Bloodstain Pattern Analysis. Reconstruction of events from spatter geometry. Sits outside this syllabus bullet but commonly tested in short-answer form alongside detection.
- Cut-Off Concentration
- The threshold analyte concentration, set by regulatory guidance, above which a specimen is reported as a screen-positive. Choosing the cut-off balances sensitivity...
- Detection Window
- The period after last use during which a drug or its metabolite is detectable in a given matrix. Varies from minutes (blood,...
- EMIT
- Enzyme-Multiplied Immunoassay Technique. Homogeneous immunoassay where drug-enzyme conjugate competes with drug in the sample for antibody binding; free conjugate retains enzyme activity,...
- False Positive
- A test result that indicates the presence of a target analyte when it is absent. In forensic serology this may mean incorrectly...
Explained in these topics
- Biological Sample Screening and Presumptive TestsA test with sufficient specificity to establish the identity of a biological fluid for reporting purposes. Examples include Takayama and Teichmann crystal test...
- Body-Fluid Identification: Presumptive and Confirmatory TestsA species- or analyte-specific test that provides the level of certainty required for a scientific report and court evidence. Immunochromatographic strips targ...
- Detection and Identification of Blood Stains in Forensic ScienceA specific laboratory test that establishes the substance is blood. Lower sensitivity than presumptive, much higher specificity.
- Drugs of Abuse: Screening and Confirmation ProtocolsA specific chromatographic-mass-spectrometric method (GC-MS or LC-MS-MS) that identifies the exact analyte at or above a lower cut-off. Specific and defensible...
- Kastle-Meyer TestA test specific to a substance that follows a positive presumptive result. For blood, common confirmatory tests include the Takayama crystal test, the Teichman...
- Teichmann and Takayama Crystal TestsA test that specifically identifies a substance rather than merely indicating its possible presence. In forensic serology, confirmatory tests follow presumptiv...