Half Life of Detection and Cut Offs in Urine Drug Screening

Drug screening tests offer a fast and reliable way to demask a possible drug consumer. Various tests are available as individual tests for 12 drugs and medications as well as different combinations are offered which can be used in diverse circumstances, according to customer needs (Table V-4). They range from quick, competitive, stringent immunoassays to directly qualitative indications of drugs in urine. Depending on the time of abuse there is a large variability in half-life during which the agent can be detected in urine specimen.

The cut-offs presented in the next table are those used for immunoassays in federally mandated urine drug testing programs [59]. The detection time of a drug in urine indicates how long after administration a person excretes the drug and/or its metabolite(s) at a concentration above a specific test cut-off concentration [69, 71]. Although it is governed by several factors, including dose, route of administration, metabolism, urine volume, and pH, the detection time of most drugs in urine is less than 5 days, typically 1-3 days [21, 69, 70]. Long-term use of lipid-soluble drugs, such as marijuana, diazepam, or phencyclidine, may extend the window of detection to as long as a month [59, 21, 69].

At the cut-off value of 1000ng/mL, urine samples can be positive for amphetamine for up to 5 days after intake [69]. On average, after smoking one marijuana cigarette, tetrahydrocannabinol (THC) may be detectable for 2-4 days in urine; more frequent users can be positive for a month [69]. Street doses of cocaine may be detectable for up to a week [69]. The detection time for opiates is about 1-2 days [65, 69]. Note that a positive "opiate" screen demonstrates the presence of codeine or morphine (a metabolite of heroin) only. The duration of detectability of phencyclidine is 8 days, though it may be detectable for up to a month in chronic users [59, 21].

Table V-4. Length of detection of different abused drugs in the urine (PCP = phencyclidine; TCA = tricyclic antidepressants; EDDP = 2-ethylidin-1, 5-dimethyl -3, 3-diphenyl-pyrrolidine)

Amphetamine

1-3 days

Barbiturates

4-8 days; in the case of chronic abuse, several weeks

Benzodiazepines

3 days after therapeutic dosage; up to 4-6 week in the case of long-term usage

Buprenorphine

2-6 days

Cannabis

The half-life is several weeks. Due to its good fat solubility, strong usage of cannabis can be positively detected in urine tests even after 20-30 days.

EDDP (methadone

2-7 Days

metabolite)

Cocaine

Half-life ca. 90 min. With a cut-off of 300 ng/ml, detectable after about 2-4 days

Methadone

2-5 days

Opiates/Opioids

2-3 days

PCP

2-3 days

TCA

2-3 days

Table V-5. The cut-off values of different agents used in urine drug screening (EDDP = 2-ethylidin-1, 5-dimethyl -3, 3-diphenyl-pyrrolidine; AMP = amphetamine; MET = methamphetamine)

Drug

Cut-off Value (ng/ml)

AMP300

300

Amphetamines

1000

Barbiturates

300

Benzodiazepines

300

Buprenorphine

20

Cannabinoides

50

EDDP

100

MET300

300

Methadone

300

Methamphetamines

1000

Cocaine

300

Opiates

300

TCA

1000

According to the individual cut-off values, drugs can be detected in urine down to a specific concentration. Anything below the specific cut-off value will not be identified (Table V-5).

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