Drugs of Abuse: Screening and Confirmation Protocols
UGC-NET Paper 2 Unit IV notes on drugs-of-abuse screening and confirmation: SAMHSA cut-offs, immunoassay-to-GC-MS workflow, matrices, NDPS sampling.
Last updated:
Drugs of abuse testing is the bullet in UGC-NET Forensic Science Unit IV that ties forensic toxicology to immunoassay, chromatography and the NDPS Act in a single workflow question. The syllabus asks you to recall the two-tier pipeline (screen then confirm), the SAMHSA cut-off concentrations, the matrices and detection windows, and the Indian sampling rules under NCB Standing Orders. NTA tends to write MCQs that pair a screening technique with the correct confirmation method, or that ask which matrix gives the longest window of detection.
Treat this as a workflow topic with a memorisation layer on top. Learn the SAMHSA-5 panel, the cut-off numbers, the immunoassay family (EMIT, CEDIA, FPIA, KIMS, lateral-flow), the GC-MS and LC-MS-MS derivatisation hooks, and the adulteration-detection logic. The book chapters on drug metabolism, hair analysis and hyphenated techniques cover the underlying chemistry; this UGC-NET topic gives you the exam-ready frame.
- Screening test
- A fast, sensitive immunoassay (EMIT, CEDIA, FPIA, KIMS, lateral-flow) that flags a sample as presumptive positive against a class cut-off. Sensitive and cheap, but cross-reactive: positive result is not proof.
- Confirmatory test
- A 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 in court.
- SAMHSA-5
- The five-drug federal workplace panel of the US Substance Abuse and Mental Health Services Administration: amphetamines, cocaine metabolite, marijuana (THC-COOH), opiates and PCP. Adopted as a starting reference by most Indian and international labs.
- Cut-off concentration
- A pre-fixed analyte concentration (ng/mL) that defines positive vs negative. A separate, lower confirmation cut-off applies to the GC-MS or LC-MS-MS step.
- Detection window
- The period after last use during which a drug or its metabolite is detectable in a given matrix. Varies from minutes (blood, oral fluid) to months (hair).
- 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, measured spectrophotometrically.
- MRM
- Multiple Reaction Monitoring. LC-MS-MS or GC-MS-MS mode that follows specific precursor-to-product ion transitions for each target analyte, giving very high selectivity at low concentrations.
- Adulteration
- Deliberate tampering of a urine specimen to defeat the screen. Common adulterants include nitrite, chromate, peroxide, glutaraldehyde, niacin, vinegar and Visine. Detected by specimen-validity testing of pH, specific gravity, creatinine and oxidisers.
The two-tier workflow NTA loves to test
Screen first, confirm second. Never the other way round.
Drugs-of-abuse testing in forensic, clinical and workplace settings runs as a strict two-tier pipeline. The first tier is a fast, cheap, very sensitive immunoassay screen. The second tier is a slow, specific, mass-spectrometric confirmation. NTA writes MCQs around this split because the reasoning is identical to the presumptive-versus-confirmatory logic in bloodstain testing, and the wrong-answer distractors are easy to construct.
Screen first because the lab has to triage hundreds of samples a day. A urine immunoassay gives a yes / no answer in minutes against a class cut-off (for example, 500 ng/mL for amphetamines), which lets the lab discard all true negatives without using expensive instrument time. Confirm second because immunoassays are class-specific, not analyte-specific: an opiate screen does not tell you whether the morphine came from poppy seeds, codeine, prescription pethidine or heroin (via the 6-MAM metabolite). Confirmation by GC-MS or LC-MS-MS gives the molecular identity with a retention time plus a fragment ion pattern that survives cross-examination.
The cardinal rule for MCQs: a positive screen is not a positive result. Only a confirmed analyte at or above the confirmation cut-off, on a properly collected and chain-of-custody-protected specimen, is reported as positive.
The SAMHSA-5 panel and the cut-off numbers
Five classes, two cut-offs each. Memorise the table.
The US SAMHSA workplace panel is the global reference grid that most Indian forensic and clinical labs adapt for their own SOPs. NTA frequently asks for cut-off numbers, so memorise them in the standard ng/mL urine units.
| Class | Screen cut-off (ng/mL urine) | Confirm cut-off (ng/mL urine) | Confirmation target analyte |
|---|---|---|---|
| Amphetamines (AMP, MAMP) | 500 | 250 | Amphetamine, methamphetamine |
| Cocaine metabolite | 150 | 100 | Benzoylecgonine |
| Marijuana (cannabinoids) | 50 | 15 | 11-nor-9-carboxy-THC (THC-COOH) |
| Opiates | 2000 | 2000 | Morphine, codeine |
| Heroin marker | 10 | 10 | 6-acetylmorphine (6-MAM) |
Matrices and detection windows
Different matrices answer different questions: recent use, chronic use, intoxication.
The choice of matrix determines what question the test can answer. For UGC-NET, learn the windows in rough order of magnitude.
| Matrix | Window of detection | What it tells you | Practical notes |
|---|---|---|---|
| Blood | Minutes to hours (up to 1 to 2 days for some drugs) | Current intoxication and impairment | Invasive collection. Standard for driving-under-influence and post-mortem casework. |
| Urine | Hours to a few days (cannabinoids up to weeks in chronic users) | Past use, not impairment | Most common matrix. Easy to adulterate; specimen validity must be checked. |
| Oral fluid (saliva) | Minutes to about 24 hours | Recent use, correlates loosely with blood | Observed, non-invasive collection. Used in road-side roadside drug testing kits. |
| Hair | Weeks to months; segmental analysis at about 1 cm per month | Chronic exposure history | Detects past use, not recent use. External contamination must be excluded by washing. |
Screening methods: immunoassay families
EMIT, CEDIA, FPIA, KIMS, lateral-flow; pick the family for the setting.
All screening immunoassays use the same antibody-against-drug principle but differ in label, format and instrumentation. NTA tests the full-form expansion and the broad principle.
EMIT (Enzyme-Multiplied Immunoassay Technique). Drug in the sample competes with drug labelled to glucose-6-phosphate dehydrogenase (G6PDH) for antibody binding. Antibody-bound conjugate is enzymatically inactive; free conjugate oxidises NAD to NADH and is measured at 340 nm. Homogeneous (no separation step), runs on any clinical chemistry analyser, and is the workhorse of Indian SFSL drug screens.
CEDIA (Cloned Enzyme Donor Immunoassay). Two genetically engineered inactive fragments of beta-galactosidase reassemble into the active enzyme; drug bound to the enzyme-donor fragment can be blocked from reassembly by antibody. Free drug in the sample frees the enzyme-donor fragment, restoring activity. Used for benzodiazepines and methadone.
FPIA (Fluorescence Polarization Immunoassay). Fluorescein-drug conjugate rotates fast and depolarises light when free; rotation slows when antibody-bound, so polarisation rises. Inverse competition. Now less common because the proprietary instrument has been discontinued, but still tested.
KIMS (Kinetic Interaction of Microparticles in Solution). Drug-coated microparticles aggregate when antibody crosslinks them, increasing turbidity. Free drug in the sample inhibits aggregation. Read at a fixed wavelength on a clinical analyser. Common on Roche cobas platforms.
Lateral-flow rapid kits. Dipstick or cassette immunoassays with antibody-coated capture lines. Drug in the sample blocks the binding of the gold or latex conjugate, so the test line stays clear (positive) and the control line is always coloured (valid). These are the kits Indian state police carry under NDPS Section 41 for road-side and crime-scene screening. They are screening tools, never confirmatory.
The common MCQ trap is to ask which technique is heterogeneous (needs a separation step) versus homogeneous (does not). EMIT, CEDIA, FPIA, KIMS are all homogeneous; lateral-flow uses physical capture but no analyte-specific wash step.
Confirmation: GC-MS and LC-MS-MS
Derivatise, separate, fragment, identify. Then report.
Confirmation is done by GC-MS for volatile, thermally stable analytes and by LC-MS-MS for polar, thermolabile or large molecules. The rule of thumb in any forensic toxicology MCQ: if the analyte has hydroxyl, carboxyl or amine groups (like opiates, amphetamines, THC-COOH), GC-MS needs derivatisation; LC-MS-MS does not.
GC-MS with derivatisation. The polar functional groups are masked with silyl, acyl or alkyl groups to improve volatility and chromatographic peak shape.
- BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide) plus TMCS catalyst for opiates (morphine, codeine, 6-MAM): adds trimethylsilyl groups to hydroxyls.
- HFBA (heptafluorobutyric anhydride) for amphetamines and methamphetamine: adds heptafluorobutyryl groups to the secondary amine, also giving an electron-rich fragment that is easy to track in selected-ion monitoring.
- MSTFA, MTBSTFA, BSA and other silyl reagents for THC-COOH and steroids in NADA / WADA doping work.
Detection is in selected-ion monitoring (SIM) for sensitivity, monitoring three diagnostic ions per analyte with fixed retention time and ion-ratio criteria (typically within 20 percent of the calibrator).
LC-MS-MS in MRM mode. No derivatisation needed. The analyte is ionised in ESI or APCI, the precursor ion is selected by Q1, fragmented in q2 collision cell, and one or two product ions are selected by Q3. Each analyte is identified by retention time, precursor mass, two product ions and the product-ion ratio. Quantification is against a deuterated internal standard (for example morphine-d3, cocaine-d3) added before extraction. LC-MS-MS is now the dominant confirmation platform for benzodiazepines, fentanyl, novel psychoactive substances and the WADA panel.
Both platforms produce reports that survive court because the identification rests on two orthogonal dimensions (retention time and mass spectrum) at a documented concentration above the confirmation cut-off.
Adulteration challenges and specimen validity
If the matrix is compromised, the result is not defensible.
Donor adulteration is the single biggest practical problem in workplace and pre-employment urine testing. NTA does not test deep adulteration chemistry, but it does test the categories and the detection logic.
- Dilution. Drinking water or substituting tap water. Detected by low specific gravity (less than 1.003) and low creatinine (less than 20 mg/dL).
- pH adulterants. Vinegar (low pH) or ammonia / bleach (high pH). Detected by out-of-range pH (less than 4.5 or greater than 8.0).
- Oxidising adulterants. Nitrite, chromate, pyridinium chlorochromate, hydrogen peroxide. These destroy THC-COOH and morphine on the immunoassay strip. Detected by specific colour reagents on specimen-validity panels.
- Glutaraldehyde. Sold under brand names (UrineLuck and others) to denature antibodies; detected by Fujiwara-type colour tests.
- Visine eye-drops. Benzalkonium chloride masks cannabinoid antibody binding. Detected indirectly through bulk-matrix anomalies.
- Niacin / vinegar / cranberry juice myths. Folk methods, largely ineffective at the SAMHSA cut-offs but still attempted.
Indian DFSS toxicology SOP requires the specimen-validity panel to be reported alongside the drug result. A positive screen on an invalid specimen is reported as "specimen rejected" rather than positive, because the chain of attack in court is too clean otherwise.
Indian context: NDPS, NCB, DFSS and sports doping
Sampling under Standing Order 1/89, lab routing, and the section that decides the sentence.
The Indian legal frame for drugs-of-abuse casework is the NDPS Act 1985 read with NCB Standing Order 1/88 (sampling) and 1/89 (procedures for seizure, sampling and dispatch). The sampling SOP requires the seizing officer to draw two representative samples of 5 g (small quantity) or 24 g (commercial) from each homogeneous lot, seal them in cloth-and-paper packets with the case-property seal, prepare Form NCB-1 (test memo), and dispatch one sample to the relevant CFSL or state DFSS within 72 hours under a sealed-cover chain of custody. The second sample is the court sample and is opened only if a re-test is ordered.
Routing depends on the analyte and the seizing agency. NCB seizures go to CFSL Hyderabad, CFSL Chandigarh or CFSL New Delhi depending on jurisdiction; state police seizures go to the state SFSL drug section. Hospital emergency-room drug-of-abuse screens for poisoning admissions are handled by hospital clinical toxicology labs (AIIMS, PGIMER, JIPMER, NIMHANS) and follow biological matrix handling rules separate from the NDPS chain.
Sports doping in India sits in a parallel ecosystem. NADA Delhi commissions sample collection through Doping Control Officers; samples are analysed at NDTL Delhi (the only WADA-accredited Indian laboratory). NDTL follows the WADA International Standard for Laboratories with its own A-sample and B-sample architecture, which mirrors the NCB two-sample logic but is procedurally distinct.
A point that returns in PYQs and viva: NDPS Section 27 (consumption of drugs) carries a maximum sentence of one year (cocaine, morphine, heroin) or six months (other drugs), while trafficking under Sections 21, 22 or 23 attracts ten to twenty years for commercial quantity. The forensic report's quantity figure, together with the seizure weight, is what decides the section the accused is charged under, which is why the drug metabolite confirmation and the quantitative GC-MS or LC-MS-MS number are scrutinised in court.