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The Case for Point-of-Care Drug Testing
March-April 2014 - Vol. 3 No. 2 - Page #6

Given the distinct advantage of providing immediate results that can facilitate clinician-patient communication and guide clinical decisions in real time, point-of-care (POC) drug screening devices are now widely used in medical practice. As such, urine drug testing (UDT) is commonly used with patients who have been prescribed opioid analgesics and other controlled substances to verify adherence with prescription instructions and to detect the use of any non-prescribed or illicit drugs. Although laboratory-based UDT is more reliable due to the accreditation requirements for test validation in that setting, (which also may offer a broader testing menu), urine specimens must be sent to a central laboratory (or shipped to a remote laboratory) requiring hours or even days for results turnaround. Therefore, the analytical limitations of POC UDT are sometimes outweighed by the benefits of convenience and immediate resulting.

Single-use POC devices, such as those most commonly used for UDT, are usually more expensive on a unit-cost basis when compared to automated laboratory methods due to the attendant costs associated with manufacturing and disposability, but the balance is changing. Automated laboratory methods for UDT typically involve minimal reagent costs; this is true even for highly sophisticated mass spectrometric applications. However, clinical laboratories also incur significant indirect costs related to the personnel, facility, and capital equipment factors that are allocated to all individual tests, proportionately. As with all test utilization, these indirect costs depend on the total number of tests performed by the laboratory—a high-volume laboratory will generally have a lower cost per test compared to a smaller laboratory. Furthermore, the incremental cost of a single urine drug test is minimal for a laboratory that has already invested in automated analyzers capable of performing UDT in addition to many other tests.

Economics of POC Testing
There are additional components to the economics of POC testing that are more difficult to quantify. For example, POC UDT can save the clinician time by obviating the retrieval of laboratory results (often after the patient has already left the office or hospital) and eliminating the need to contact the patient for follow up. Furthermore, addressing a patient’s needs in a single encounter, as opposed to having them wait for a follow-up call or appointment when the UDT results become available, is more convenient for the patient, perhaps rendering the health care facility more competitive than other health care facilities that offer similar services. Increased efficiency and augmented service provision are POC UDT factors that can translate into tangible downstream financial benefits.

Another consideration with regard to the economics of POC testing is the cost and applicability of regulatory compliance. Most POC UDT devices are CLIA-waived and require only a Certificate of Waiver, along with implementation of certain measures (policies and procedures) to ensure the test is being performed in accordance with the manufacturer’s instructions. However, some POC UDT devices are not CLIA-waived and the requirements for regulatory compliance with non-waived laboratory tests are considerably more extensive. Typically, waived devices require minimal training to operate and there are no CLIA-prescribed educational or experience requirements for users, whereas non-waived methods can only be performed by personnel who meet the requirements specified under §493.1423 F.A.C., including, at a minimum, an associate degree in a chemical, physical, or biological science, or military training as a laboratory technician. The need to gain and maintain regulatory compliance—including factors such as enrollment in a proficiency testing program, method validation studies, correlation of results between multiple instruments, quality assurance procedures, etc—will add overhead to the cost of providing non-waived POC tests. The magnitude of that contribution to the overall cost of UDT will depend primarily on the device used; for CLIA-waived POC UDT devices, the overhead is minimal.



Patient-centered Benefits of POC
While it is important to focus attention on the economics of POC UDT—the intangible benefits often can outweigh the sometimes higher per-unit cost for POC devices and they are likely to provide a less expensive option for the payer—perhaps the greatest benefits of POC UDT accrue from their influence on the clinician-patient encounter by providing results in a setting that readily promotes discussion. For clinicians, the unique advantage of POC UDT is that it provides laboratory results that can be used in the clinical encounter while it is happening. There is no substitute for a contemporaneous face-to-face conversation with the patient about the meaning of today’s drug screen result.

When the test results confirm expectations, the clinician can provide the patient with immediate positive reinforcement for adherence to the treatment plan—an especially important benefit for patients with a history of drug-related problems. Additionally, expected UDT results give the clinician an immediate degree of confidence that prescriptions written during that encounter are appropriate.

For potentially inappropriate results, there are more important advantages of POC UDT. First, patients do not have to wait to be called—or called back to the office—days or weeks later, after laboratory results have been received and reviewed, thereby alleviating patient anxiety. POC testing also can mitigate the logistical difficulties associated with busy clinical practices and patients who may be unavailable for follow-up phone calls or visits. Second, potentially inappropriate results should prompt a discussion with the patient about their use of all prescription, over-the-counter, herbal, and illicit drugs; patient recall is freshest and most reliable at the time of urine collection. Third, non-adherent patients have less time to construct convincing alternative narratives to explain their inappropriate test results, and clinicians can pick up important verbal and nonverbal cues about the veracity of their patients’ explanations.

Finally, POC UDT results provide skilled physicians with the opportunity to leverage the uncertainty inherent in POC results to strengthen the therapeutic relationship. Physicians can elicit honest disclosures about drug use at the screening stage, where trust can be built or maintained. Honest disclosures can spur motivational interviewing, brief interventions, immediate and appropriate changes in the pharmacologic plan, and timely referrals for drug treatment. These immediate conversations have the potential to promote cost-effective, patient-centered, targeted confirmatory testing, rather than reflexive confirmatory testing of all laboratory-based positive screening results. Viewed in this way, physician payments associated with POC testing can defray the costs of the test devices themselves, as well as the time spent counseling the patient in response to the results.

Effective Range of Immunoassay for Drugs of Abuse
Clinicians should be aware of the fundamental limitations of immunoassay drug screening, whether by POC or by laboratory-based platforms. Mainly, these tests are not “general” drug screens; no currently available methods are capable of detecting all analytes of interest. Currently, POC devices for UDT are limited to about a dozen drugs, drug classes, or drug metabolites. Some immunoassays (eg, for opiates or benzodiazepines) are class-specific, with limited cross-reactivity to many commonly prescribed members of a drug class, creating the potential for clinical false negative results. Moreover, some immunoassays are not specific and will cross-react with analytes with similar (and sometimes dissimilar) chemical structures, creating false positive results.

There are at least five instances in which POC (and laboratory-based) screening results might merit additional testing by a reference laboratory (including examples):

  • If a POC test result is presumptively positive for an analyte that should be absent (cocaine metabolite) and the patient denies use, confirmatory testing should be requested.
  • If a POC test result is presumptively negative for an analyte that should be present (prescribed morphine and a negative POC opiate test result) and the patient claims recent use of the prescribed opioid, confirmatory testing should be requested.
  • If for this particular patient a class-specific result is insufficient (the patient is prescribed morphine, but the clinician suspects other opiate use), testing for a specific analyte should be requested.
  • „If a quantitative result is desired (serial THC-COOH concentrations in a patient who claims to have given up cannabis use) serial quantitative testing should be considered.
  • If the pre-test probability of drug use is sufficiently high (a history of benzodiazepine dependence and suspected benzodiazepine use) despite a negative POC screening result, confirmatory testing may be appropriate.

Confirmatory testing in the above contexts is imperative if the presumptive test result will have serious clinical consequences, such as a change in the treatment plan or dismissal from a medical practice.

Understand the Capacity of POC Testing
Although the US Food and Drug Administration (FDA) originally defined CLIA-waived tests as so simple and accurate as to render the likelihood of erroneous results negligible; or pose no reasonable harm to the patient if the test is performed incorrectly,1 this is certainly not the case for POC UDT. Correct interpretation of visual results using these devices is subjective. Moreover, interpretation of test results can be deceptively difficult.

Clinicians who use POC testing devices should be familiar with all aspects of their performance prior to implementation, including interpretation of results. Clinical office staff involved in POC testing also should undergo training that includes examination and acknowledgement of the following:

  • Expiration date(s) of the POC device
  • Examination of the urine specimen for temperature and appearance
  • Reading the results within the recommended time interval
  • Examining specimen validity measures (eg, temperature, specific gravity, pH, oxidants) on the device
  • Verifying the presence of control lines for each analyte
  • Understanding the difference between presumptive positive and negative results (eg, the counterintuitive results of many devices, in which the presence of a line signifies the presumptive absence of the analyte)
  • The non-quantitative nature of these assays
  • Interpretation of faint lines that do not signify the presence of “a little bit” of the analyte
  • The importance of proper conditions (eg, adequate time and lighting) for correct reading and recording of result

Conclusion
All told, the future of POC testing for drugs of abuse is uncertain, particularly in non-emergency settings, as the drug-testing marketplace is crowded, competitive, and rapidly evolving. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is an example of an emerging technology for drug screening as well as for confirmation. As the cost of laboratory-based testing comes down, POC test-device manufacturers will need to adapt in order to remain viable. The unique advantage of these devices is their ability to provide immediate results, but this might not be enough to spur widespread and persistent adoption. The devices must be user-friendly and of high quality; test menus must evolve to include the most common drugs of therapeutic use and misuse; and the quality, speed, and courtesy of customer service must rival that of the large commercial laboratories for POC UDT to be the method of choice for lab services.

Reference

  1. US Food and Drug Administration. CLIA Waivers: Medical Devices. The Regulations (42 CFR part 493). Available at: www.fda.gov/medicaldevices/deviceregulationandguidance/ivdregulatoryassistance/ucm124202.htm

Roger L. Bertholf, PhD, is a professor of pathology and laboratory medicine at the University of Florida College of Medicine, as well as director of clinical chemistry, toxicology, and point of care testing at UF Health/Jacksonville. He earned his doctorate in biochemistry from the University of Virginia and completed fellowships in clinical chemistry and neuropathology research. Roger is a diplomat of the American Board of Clinical Chemistry, with certificates in both clinical chemistry and toxicological chemistry, and also is editor in chief of Lab Medicine, published by the American Society for Clinical Pathology.

Gary M. Reisfield, MD, is director of pain management services, division of addiction medicine in the department of psychiatry at the University of Florida College of Medicine in Gainesville. He earned his medical degree at George Washington University, completed a residency in anesthesiology and a fellowship in addiction medicine at the University of Florida, and completed a fellowship in pain medicine at Massachusetts General Hospital and Harvard Medical School. Gary is board-certified in each of these three specialties.

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