**4. Interpretation of UDT results**

36 Toxicity and Drug Testing

meet this requirement. One reason for this is that immunoassays require separate analytical channels for each assay and this limits the number of tests a smaller laboratory may have in its menu (Olympus Au640 Product Information; Siemens V-Twin Analyzer Product Information; Thermo Fisher Mgc-240 Analyzer Product Information). Another reason is that certain drug tests may not exist for the laboratory's specific instruments, and the addition of another instrument is financially prohibitive, particularly if that instrument is a mass spectrometer (Agilent Technologies, Inc.). Many physicians treating the pain patient population send specimens to reference laboratories specifically designed to provide the required test menu to meet these needs. Tests for new drugs (i.e., tapentadol) (Nucynta - Tapentadol, 2010) or new illicit substances (i.e., K2, spice) (Sobolevsky et al., 2010; Vardakou et al., 2010) encountered in the pain patient population can be rapidly set up and validated on LC-MS/MS instrumentation. Therefore, this analytical technique is supplementing screening by immunoassay. Because of the limitations of immunoassays, confirmatory testing is essential for accurate clinical assessment of medication usage. With confirmatory testing, physicians have specific evidence of what medications a patient is or isn't taking. This assures the doctor that he or she is not discharging a patient inappropriately, and that care is appropriate and not limited.. The laboratories with the most advanced technology can eliminate the

At this point in time, mass spectrometry is considered the method of choice for UDT analysis in pain management. This is because mass spectrometry offers the chromatographic separation and mass fragmentation patterns that are specific for the test medications such as opiates and benzodiazepines (Mohsin et al., 2007). In addition, this analytic approach uses isotope dilution to quantify the amount of drug in the urine specimen; isotope dilution is considered the gold standard for determining how much of a drug is in a specimen (quantitation) (Federal Register, 2004). This ability to quantify the amount of drug in urine has been proposed as a method of detecting drug abuse (Pesce et al., 2010c). However, it is important to note that it is not possible to relate the quantitative excretion of a drug to the drug dosage (Nafziger & Bertino, 2009). Quantitation of drugs using immunoassay technology is problematic, particularly if the antibody reagent cross reacts with multiple structurally related drugs; if the urine drug sample contains more than one drug in a class (i.e., hydrocodone and hydromorphone), the antibody reaction will vary with each drug present in the solution. This means that the assay cannot distinguish between the two drugs and give a reliable calculation of the amount of either

Of the two commonly used mass spectrometry methods, LC-MS/MS offers several advantages over GC-MS (Mikel et al., 2010). These include the ability to discriminate a larger number of drugs in each test run, the very small amount of urine specimen required (as little as 25 microliters, or one drop), and the ability to use a sample that is neither derivatized nor extracted. This in turn has made possible the analysis of hundreds of urine specimens per day for a single mass spectrometer. Advances in the automated handling of specimens and bar coding allow for the accurate processing of thousands of samples per day. This method of analysis can provide physicians with results more rapidly than by GC-

immunoassay step saving both the patient and the insurer money.

**3.6 Mass spectrometry as the gold standard for testing** 

drug present (Feldkamp, 2010).

MS (Mikel et al., 2010).

The accurate interpretation of test results requires an understanding of the usefulness and limitations of immunoassays (Gourlay et al., 2010; Hammett-Stabler & Webster, 2008; Manchikanti et al., 2010; Nafziger & Bertino, 2009; Reisfield et al., 2007), a knowledge of opiate metabolism, and awareness of the expected ratios of the parent drug and its metabolites in urine (Reisfield et al., 2007). In addition, small amount of impurities in medications detectable by mass spectrometry can complicate the interpretation of UDT results. For example, codeine is present in morphine preparations and hydrocodone is present in oxycodone preparations (Evans et al., 2009; West et al., 2009, 2011b). Physicians who aren't aware of the presence of these impurities may wrongly dismiss a patient because he or she tested positive for codeine or hydrocodone when it was not prescribed. The presence of both parent drug and its metabolite in a urine sample readily measured by mass spectrometry can reassure the physician that the patient is taking the medication and that it is being metabolized appropriately. Also, for some drugs such as carisoprodol, fentanyl, or buprenorphine, only the metabolite may be observed. It is imperative that physicians prescribing these medications use a reference laboratory that is able to measure both the parent drug and its corresponding metabolite and be able to present interpretive results for the physician (Heltsley et al., 2010). Creatinine is a metabolic breakdown product that is present in urine. The amount of creatinine excreted into urine is nearly constant for any individual. Reference laboratories calculate the amount of drug excreted per gram of creatinine, which allows the monitoring of excreted medication or illicit drug over time. This information is useful to physicians in certain circumstances because some drugs, such as nordiazepam remain in the system long after a person stops taking them. A UDT result that is not corrected for creatinine may show that the patient is more positive for the drug than on a previous test, even though the patient has in fact stopped taking it. Except for changes in the patient's renal status, or loss from adipose tissue due to dieting, this conflicting result may be due to the second urine being more concentrated than the first. A creatinine-corrected value will correct for a patient's hydration on the day of the test and show a decrease in the amount of nordiazepam in the urine, thus supporting the patient's claim that he or she has stopped taking the drug. It is important that reference laboratories not only provide creatininecorrected results but that they give doctors or staff help in interpreting the data (Cone et al., 2009). It is also important for the physician to know if a patient has attempted to obscure UDT results by diluting a urine specimen. To accomplish this, he or she must have a grasp of creatinine and specific gravity UDT validity tests (Wu, 2001). Laboratory staff who interface with clients should provide this information when questions arise.
