Urinary Drug Testing in Pain Management
Physicians have been forced to weigh professional risk in selecting a treatment modality when treating patients for chronic pain for fear of civil, administrative, or worse, criminal liability. Urinary drug testing is becoming the cheapest insurance for liability protection in clinical practice. The Federation of State Medical Boards (FSMB) adopted a policy for prescribing controlled substances stressing the critical importance in documenting, evaluating, and monitoring controlled substances in the management of pain patients. This is consistent with the guideline set forth by federal agencies including the Drug Enforcement Agency (DEA). Part of this policy — dealing with the implementation of monitoring drug compliance — is the regular use of UDT.
Clinically, the benefits of UDT are multiple. These include reducing the risk for toxicity in patients vulnerable to adverse drug effects, avoidance of medico-legal problems, detecting patient non-compliance, reducing the risk of therapeutic failure, and avoiding or detecting drug-drug interaction. Additionally, UDT enhances the physician’s ability to use drugs effectively and minimizes treatment costs.
Unfortunately, physicians have utilized UDT as a means of discharging patients from their practice. Urine drug testing should not be primarily used as a tool for protecting the doctor’s license or the pain clinic, but to enhance patient care. It has to be emphasized that the use of UDT is never intended to be punitive. It is a disservice to the medical profession for a patient to be discharged on the basis of a positive UDT. The presence of illicit substance in the urine indicates that the patient has a problem and therefore needs help and guidance from the clinician. Instead of discharging the patient from the practice, the patient should be offered help in the form of consultation and treatment with an addiction medicine specialist, psychiatrist or clinical psychologist specializing in the management of addiction, as well as enrollment in a recovery program. The patient should be managed by other means since there are a multitude of options available to treat chronic pain without necessarily using chronic opioid therapy.
The use of long term opioid therapy for chronic pain is now accepted as standard medical practice in patients with moderate to severe pain who failed to respond to more conservative therapy. Unfortunately, patient self-reporting of drug compliance is frequently unreliable and it becomes necessary to use “external” sources of information on patient drug use including pharmacy profiling, review of medical records, interview with family members, the use of some form of prescription monitoring program, and — more accurately — detecting the presence of drugs in the patient’s system using a variety of specimen such as saliva, blood, hair, and urine.
Urine is the standard body fluid tested for drug screening because it is readily available, it is easily collected, and it is easily handled by laboratory and office personnel. Urinary drug testing has been preferred over serum sampling because the period of detection of a particular drug in the urine is increased, while drugs and their corresponding metabolites may only be detectable in the serum for a short period of time. Urinary drug testing(UDT) is also less expensive and non-invasive compared to serum testing.
It has to be emphasized that the result of urine toxicology for the purpose of detecting patients who may be diverting, supplementing or abusing the prescribed drugs and other illicit substances are protected by the physician-patient confidentiality rule and the result of the test cannot be disseminated to other interested parties without the expressed consent of the patient.
Urine Drug Testing Methodology
There are two types of drug testing used in clinical practice. The first type is an immunoassay test. This test is approved by the United States Food and Drug Administration and is based on the principle of competitive binding. A known amount of antibody and an enzyme labeled drug or metabolite are added to the urine specimen. The drug or metabolite in the sample competes with the labeled drug or metabolite to bind antibody, forming an antigen-antibody complex. The amount of enzyme-labeled antigen that binds with the antibody is inversely proportional to the amount of drug or metabolite in the urine sample. The main advantage of immunoassay is allowing simultaneous and rapid testing of drugs in the urine. Immunoassays that are commonly used include radioimmunoassay, fluorescence polarization immunoassay, enzyme mediated imunoassay, and kinetic interaction of microparticles in solution.
The most sensitive and reliable of all immunoassay techniques in testing for abused drugs is the Fluorescence Polarization Immunoassay (FPIA). It has a lower level of quantification compared to the federally regulated concentration. Interference and tampering of specimens have found FPIA to be quite resistance to normal adulterating and tampering substances. The test detects the “Federal Five” drugs or drug classes that are tested in federal employees and federally regulated industries. The drug/class detected include marijuana, cocaine, opiates, phencyclidine (PCP), and amphethamines/methamphetamines. Additionally, it detects other substances such as benzodiazepines and barbiturates. However, there is no reliable relationship between the urine drug concentration and the doses taken of the prescribed drugs. Table 1 shows the comparative cutoff concentration between the standard (federally mandated) level and that of the Flourescence polarization immunoassay (FPIA).
Table 1. Comparative cutoff concentration and doses of prescribed drugs.
Unfortunately, this test has a high false positive results because of structural similarities between a variety of drugs. Patients eating poppyseed-containing food such as cakes, bagels, rolls, Danish pastry, strudels, and muffins can have a false positive test for opioid because poppyseed contains a small amount of morphine. Sympathomimetic amines, such as ephedrine and pseudoephedrine as well as certain diet pills, can produce a false positive test for amphetamine. A false positive result for marijuana can be caused by dronabinol- and hemp-containing food. The primary metabolite of cocaine is benzoylecgonine. Both cocaine and its metabolite have a low cross-reactivity with other substances. A positive FPIA is highly predictive of cocaine use.