Urine drug testing for a variety of substances, including opioids, is ubiquitous, practically a reflex, in the ED. The current opioid epidemic has expanded urine drug testing to outpatient treatment centers and physicians' offices to assess proper participation in drug addiction treatment programs. And it's not without reason: Hydrocodone (Vicodin and others) was the second most dispensed medication in the entire country in 2015. Opioids are now prescribed three times more frequently in the United States than they were in 1999 and four times more frequently by physicians here than by European clinicians. The use of opioids to treat chronic nonmalignant pain has skyrocketed. Many opioids, especially fentanyl and analogues, are also available on the street.
Unfortunately, many painful conditions require opioids, although scientific data proving their efficacy over other interventions are somewhat weak and firm science to back up this practice can be shaky. Neurologic pain, for example, is best treated with nonopioids. It is currently estimated that about two million people struggle with opioid addiction in the United States. About 30,000 individuals died from opioid overdose in 2015, an 11 percent increase from 2014.
The reasons for urine drug testing for abused substances differ in office and clinic practice compared with the ED. It is commonly used to evaluate patients in the ED, but the actual benefit of a urine drug screen to substantiate a specific diagnosis or to guide treatment is minimal. Even the otherwise prescient and sagacious clinician's knowledge of the value, accuracy, and intricacies of urine drug testing can be marginal.
Role of Urine Drug Testing in the Current Opioid Epidemic
This article describes some important issues concerning urine drug testing for opioids. Compared with blood, hair, sweat, and saliva, urine testing offers a number of benefits that have made it a common test in the clinic and ED. Point-of-care testing is easily accomplished, although turnaround times may be a few hours. Drug screening has become common in pain medicine practices as well.
Testing on urine starts with an immunoassay to analyze for classes of drugs that are present or absent. This type of testing employs antibodies to morphine to test for opioids, and the class tested for is opiates, not opioids. Opiates are morphine and codeine; opioids are numerous substances with opiate-like activity. Morphine antibodies used in testing, however, have varying degrees of cross-reactivity with structurally related substances, especially semisynthetic opioids. Opiate testing will therefore produce positive results for other opioids. The details depend on specific structure and substance concentrations.
The initial basic immunoassay is aimed at identifying only codeine, morphine, and 6-monoacetylmorphine (the first metabolite of heroin). The ability to find all semisynthetic opioids, such as hydrocodone (Vicodin), hydromorphone (Dilaudid), and oxymorphone (Opana), varies with each lab and with the drug concentrations in the urine because some semisynthetic opioids cross-react. Note that oxycodone is not found on the initial opiate screen and must be tested for individually, as is required for methadone and buprenorphine. Do not assume that even a significant overdose of semisynthetic opioids will turn up as positive on the hospital's opioid screening test. Fentanyl, the most common addition to or substitution for heroin on the street is not found on any immunoassay testing. Usually it's a test that must be sent to an outside lab, but hospital laboratories are expanding so some can detect it.
The ability of hospital laboratories to detect some synthetic opioids is limited. Clinicians should periodically contact the lab to find out exactly what is being tested when opioid screening of the urine is requested. It's usually not an extensive opioid screen but an immunoassay test for a few substances. Morphine or codeine is readily found on even the most basic immunoassay test. Oxycodone, a commonly abused opioid, must have a separate test performed to confirm its presence.
Many hospitals may need to send expanded screens to an outside lab, eliminating any value for the emergency clinician. The cost of testing is related to the number of substances analyzed, ranging from a few hundred dollars to a few thousand depending on the scope. Most importantly, each hospital decides what its opioid screen will look for, and different hospital laboratories will search for different substances. Obviously, not all opioid screens are the same.
The immunoassay is generally reliable, but a few substances will cause a false-positive opioid immunoassay test in some hospital laboratories. These include dextromethorphan, diphenhydramine, fluoroquinolones, poppy seeds, quinine, rifampin, and verapamil. Many laboratories have worked out these false-positive tests with a more sophisticated analysis.
An opioid screening test results in a positive or negative evaluation only, and is not quantitated. A positive result can be due to one of many opioids, with minimal or massive concentrations. Most hospital laboratories cannot determine the specific opioid. Methadone and oxycodone require separate tests for the lab to identify these substances.
Hospitals do not routinely confirm the results of an immunoassay test. This has no great importance in most clinical situations, but it does have certain medical and legal consequences. It is more difficult to use the test in a legal setting if the laboratory notes that it is an initial result only and confirmation is required. Confirmatory testing is usually done by a separate analyzing technique—gas chromatography-spectrometry or a liquid chromatography-mass spectrometry—that may take a few days to complete. Most hospitals do not maintain such equipment, so such confirmation requires sending the tests to an outside lab.
Immunoassay techniques in hospitals have a cut-off urine concentration that must be met for the test to be considered positive. This would usually turn positive with a very low dose. The concentration of the drug in the urine, however, is dependent on the urine concentration. An actual urine quantitative analysis is of little or no value to the clinician, and is not routinely obtained. The window of detection varies with the amount of drug taken, time from use, and concentration/specific gravity of the urine. Most opioids will be found in the urine for two to four days after a single dose. Heroin, however, is rarely ever found or even assayed. Heroin will be identified as an opioid, but it is the morphine metabolite that is detected. Overall, urine drug testing by immunoassay does not distinguish the dose taken, the time taken, the frequency of use, or when the last dose was taken. An individual may take an opioid for a headache and still be positive two days later when he comes to the ED for another problem.
Testing the urine for the presence or absence of opioids in the ED has minimal usefulness. One would not wait for the results of this test before administering naloxone to patients who are symptomatic and have a clinical scenario that fits an opioid overdose. A positive test does not always indicate that the substance found is causing the patient's symptoms.
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