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Drug Detection Periods in Urine

October 5, 2011
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How long does a drug stay in urine after use? This is a commonly asked question and one that is difficult to answer as there are many physiological and analytical factors that determine the presence of a drug in urine.

Physiological factors include the amount and frequency of use, metabolic rate, body mass, as well as urine pH.

Metabolic Rate: Individuals with slower body metabolism are prone to longer periods of urine drug detection. In general, human metabolism slows with age or during periods of deteriorating health, resulting in longer drug detection periods. When tolerance to a drug is established, a shorter detection period is expected due to faster metabolism of the drug.

Body Mass: In general, human metabolism slows with increased body mass, resulting in longer period of drug detection. In addition, chronic users, physically inactive users, and individuals with a high percentage of body fat in relation to total body mass are prone to prolonged detection for drugs known to accumulate in fatty lipid tissue, such as Cannabinoids and Phenycyclidine.

 Urine pH: Urine pH can impact drug detection periods. Typically, acidic urine results in shorter drug detection periods.

 Pre-analytical issues such as addition of specimen adulterants will affect detection of the urine drug. Dilution of the urine with water or common household products such as dish-soap, may result in a false negative test even when the drug is present at concentrations above the analytical cut-off value. However there are methods to catch cheating. Many labs assess the integrity of the urine specimen using semi-quantitative analysis of the urine pH, specific gravity and creatinine. Samples exceeding normal expected values are reported with a note and even rejected.

Analytical considerations include the cut off value used to assess a detected or non-detected response, as well as the analytical sensitivity and specificity of the method used for analysis. Therefore testing the same analyte by different methods could generate discrepant results due to differences in method. On the other hand, the length of time for detection of the drug in the urine may vary depending on whether the method in use detects all excreted forms of the drug in question, such as free drug, metabolite or conjugated with glucuronic acid.

 The following table is a summary of approximate time since last use, that a urine specimen will test positive for a selection of more common drugs of abuse. These values should be used as a general guideline only.

Approximate Drug Detection Times in Urine
Drug Days Since Last Use Cutoff Value for Drug Detection (ug/L)
Amphetamines 1-4 1000
Barbiturates 2-30 200
Benzodiazepines 1-42 200
Cannabinoids 1-35 50
Cocaine 1-4 300
Methadone 1-7 300
Opiates 1-3 300
Phencyclidine 2-30 25

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