Drug Testing Techniques
ELISA (Enzyme Labeled ImmunoSorbent Assay) is the screening technology used for hair and oral fluid drug testing. This technique involves the mixing of specifically developed antibodies with the patient's processed hair or oral fluid. These antibodies are designed to attach specifically to drugs or drug metabolites. The specific antibodies will attach to drugs present in the patient's hair or oral fluid. Automated instrumentation is used to detect this attachment of antibody to drug. If this specific attachment occurs the specimen is considered positive for the drug detected.
EMIT (Enzyme Multiplied Immunoassay Technique) is the screening technology used for urine drug testing. This technique utilizes essentially the same principles as the ELISA testing.
GC/MS (Gas Chromatograph/Mass Spectrometry) is considered a confirmatory testing technique. It is universally considered the "Gold Standard" in drug testing. This procedure involves the purification of a specimen (hair, oral fluid or urine) by the gas chromatograph and the positive identification of the purified drug by the mass spectrometer. The mass spectrometer produces the mass spectrum of the drug undergoing confirmation. The mass spectrum is as unique to a drug as a fingerprint is to an individual. The GC/MS technique provides absolute information about drugs and drug metabolites in biological specimens.
Whereas drug screening, by either ELISA or EMIT, is an extremely reliable indicator of drug use, no screening test provides 100% accuracy. Only GC/MS testing can approach this level of accuracy.
Drug Detection Times
| Drug | Urine | Blood | Oral Fluid | Hair |
|---|---|---|---|---|
| Amphetamines | 2-4 days | 2-3 days | * | |
| Barbiturates | 2-4 days (S) / 2 Weeks (L) | 2-3 days | * | |
| Cocaine | 2-4 days | 2-3 days | * | |
| Marijuana | 2-5 days (occ) / 4 weeks (chronic) | 72 hrs | * | |
| Methadone | 2-4 days | 2-3 days | * | |
| Opiates | 2-4 days | 2-3 days | * | |
| PCP | 2-5 days | 2-3 days | * | |
| Propoxyphene | 2-4 days | N/A | * | |
| Ethanol | up to 12 hrs | up to 8 hrs | up to 8 hrs | N/A |
- (S) short acting barbiturates
- (L) long acting barbiturates
- (occ) occasional usage
- * depends on hair length; each inch represents a 2 month historical record
- all times are approximate and depend on multiple factors
Interpreting Hair Drug Test Results
Hair Drug Test Results Which Are Positive
The individual was most likely a chronic user of the drug detected during the time period indicated by the length of the hair.
Hair Drug Test Results Which Are Negative
The individual was not a chronic drug user during the time period indicated by the length of the hair.
There was not enough drug incorporated into the individual's hair. It should be noted that some drugs such as amphetamines and PCP are not efficiently incorporated into hair.
Hair drug testing detects the presence of amphetamines, opiates, cocaine, PCP and marijuana only. The use of other drugs will not be detected. Alcohol (ethanol) can not be detected in hair.
Evaluation of Time Period Represented in Hair
Hair grows at a rate of approximately 1 inch every two months. Multiply the length of the individual's hair by 2 to approximate the historical drug use record in months.
Hair Results vs. Urine Results
A negative hair drug test should never be used to refute the results of a positive urine drug test. Hair drug testing is best at detecting chronic drug use whereas urine testing can detect a single drug use episode.