Urine Drug Testing for Opioids in the Rehabilitation Patient

Drug

Screening cut-off concentrations ng/mL urine

Confirmation cut-off concentrations ng/mL (non-regulated)

Confirmation cut-off concentrations ng/mL (federally regulated)

Urine detection time

Opioids

Morphine

300

2000

3–4 days

Codeine

300

2000; 300

1–3 days

Hydrocodone

300

2000

1–2 days

Oxycodone

100

2000

1–3 days

Methadone

300

100

2000

2–4 days

Benzodiazepines

200

20-50

Up to 30 days

Cocaine

300

150

1–3 days

Marijuana

1–3 days for casual use; up to 30 days for chronic use

Amphetamine

1000

100

500

2–4 days

Methamphetamine

1000

100

500

2–4 days

Heroin^*

1–3 days

Phencyclidine

2–7 days for casual use; up to 30 days for chronic use

*6-MAM, the specific metabolite is detected only for 6 h

Various factors of drug pharmacology , such as drug absorption, metabolism, or excretion, can affect UDT findings by influencing the quantity of the drug excreted in urine. Drug detection in urine samples is performed by a cut-off threshold, which is the predetermined drug concentration in the sample. Any value equal to or above the amount found in the sample is considered a “positive result”. Typical screening and confirmation cut-off concentrations and detection times for drugs of abuse are seen in Table 32.1. Depending on the cut-off levels of the testing, or of the laboratory standards, there may be more false-positive or false-negative results.

Blood concentrations of the active drug may be influenced by genetic polymorphisms on metabolism and clearance, which cause variabilities. For instance, a pro-drug, such as codeine, can be converted to morphine, and its presence in the urine may misguide the clinician to falsely believe that there was an abuse of morphine [17]. In addition, urine pH is known to affect methadone excretion, which causes lower urine concentrations of methadone at higher urine pH, as seen in conditions such as urinary tract infection, a vegetarian diet, and others [18]. Oxycodone, a semisynthetic opiate derived from thebaine, has minimal cross-reactivity with opioid screening assays. However, specific immunoassay strips are commercially available. Regular opioid UDTs are unable to detect fentanyl, or its analogs, in the urine because these compounds do not have cross-reactivity against the immunoassay antibodies designed for opioids in the urine samples. These chemicals are only be measured using gas or liquid chromatography with mass spectrometry (GC/MS, LC/MS) techniques [19].

Cross-reactivity with other chemicals that have similar structural and chemical properties as the original substance, which include over-the-counter diet agents, some antibiotics, and decongestants, are also common and can be misleading in the UDT. Similarly, NSAIDs may make UDT positive for marijuana. Bupropion, desipramine, and cold medicines may make UDT positive for amphetamines. Finally, poppy seeds, chlorpromazine, and rifampicin may make UDT positive for opioids [20]. One should realize that screening methods detect the presence of a certain chemical in the sample (above or equal to the cut-off value), and not the actual concentration of the chemical. Therefore, all positive results should be confirmed by further laboratory techniques.

Types of UDT

Two types of urine drug tests are commonly used, which include: (1) immunoassay (IA) ; (2) laboratory-based testing, such as gas chromatography/mass spectrometry (GC/MS), liquid chromatography tandem mass spectrometry (LC/MS), or high performance liquid chromatography (HPLC). IA tests that are practical, fast, and low cost, are frequently used in home-testing kits and in point-of-care (POC) screenings at outpatient clinics. IAs can detect numerous drugs and their metabolites within minutes of collection by using a pre-arranged, reactant-absorbed strips. If the sample contains any chemical that reacts with those strips, the results appear as a line on the screen. If the sample does not contain that particular substance, no reaction occurs (Fig. 32.1). The reaction of a chemical is dependent on the predetermined cut-off levels. Therefore, any chemicals in the sample, which are above or equal to the cut-off value, would make the result positive. IA test results should always be considered as presumptive until confirmed by a laboratory-based tests (GC/MS, LC/MS, or HPLC) for the specific drug. Several studies report false-positive results for cocaine and THC, in contrast to false-negatives for opiates and amphetamines [21].