**2.2 Limitations of immunoassay**

The qualitative immunoassay model of testing is only a partial UDT solution for the pain population (Gourlay et al., 2010; Hammett-Stabler & Webster, 2008; Nafziger & Bertino, 2009; Reisfield et al., 2007). There are a number of reasons for this. First, doctors treating patients for pain are concerned with negative as well as positive results. This is because a negative result can mean that a patient is not taking a prescribed medication. Second, workplace UDT assays do not fit the clinical medication regimen used in the treatment of pain patients and do not take into account the variable dosing often employed by pain patients as they try to balance their need for pain relief against the side effects of these medications (Gourlay & Heit, 2010a). In analytical terms this means that the cutoff for detection and quantitation (concentration of drug present) must be low enough to capture minimal use of the drug. Thirdly, the physicians need to have an exact indication of the medications the patients are taking. For example, a positive opiate test does not indicate whether the patient is on codeine, hydrocodone, morphine, or hydromorphone. That is, it measures the class not the particular drug. Each of these are specific medications the physician may choose to treat the patient with, so in order to establish compliance it is necessary to determine exactly which medication has been ingested and assure the patient is not taking additional opiates which could create an unsafe situation (Cone et al., 2008). Finally, if an immunoassay screening method is used, the antibody must detect all drugs of that particular class. Recent advances in designing opiate and benzodiazepine classes of drugs have resulted in agents which do not react well with the traditional antibodies. and

Diagnostic Accuracy and Interpretation

**Drug Class**

**Total Specimens Tested 106,014**

**Total Specimens Tested 167,533**

**Total Specimens Tested 133,032**

**Total Specimens Tested 168,980**

**Total Specimens Tested 104,972**

**Total Specimens Tested 104,453**

**Total Specimens Tested 80,990**

**Total Specimens Tested 166,501**

*Buprenorphine* 6,308 *6.0%*

*Cannabinoids* 11,752 *11.3%*

*Carisoprodol* 13,302 *16.4%*

*Cocaine* 4,951 *3.0%*

specimens. Test dates: 10/01/09–4/29/10.

*Alcohol* 10,594 *10.0%*

*Amphetamines* 7,005 *4.2%*

*Barbiturates* 4,797 *3.6%*

*Benzodiazepines* 60,160 *35.6%*

of Urine Drug Testing for Pain Patients: An Evidence-Based Approach 29

Ethyl Glucuronide 8,602 81.2% 59,827.9 7,220.1 500.47 - 5,942,830 500 Ethyl Sulfate 6,644 62.7% 18,660.7 3,546.1 500.17 - 1,565,150 500 Ethanol (Screen) 2,410 22.7% 735.1 mg/dL 68.6 mg/dL 20 - 151,316 mg/dL 20 mg/dL

Amphetamine 6,045 86.3% 8,471.2 2,790.2 100.31 - 409,816 100 Methamphetamine 1,178 16.8% 18,217.8 3,263.8 105.12 - 453,763 100 MDA 961 13.7% 1,771.1 844.5 101 - 416,68.9 100 MDMA 74 1.1% 5,328.2 1,260.6 120.14 - 40,395.3 100

Barbiturates (Screen) 4,797 100.0% 927.8 904.0 200 - 15,886 200

α-Hydroxyalprazolam 26,954 44.8% 479.9 177.3 20 - 55,249.1 20 Oxazepam 18,475 30.7% 2,036.0 617.4 40 - 203,128 40 7-Amino-Clonazepam 16,466 27.4% 674.6 287.0 20.01 - 47,501.7 20 Temazepam 15,647 26.0% 5,552.3 851.9 50 - 752,950 50 Nordiazepam 12,758 21.2% 693.9 281.5 40 - 25,864.3 40 Lorazepam 6,390 10.6% 1,583.1 681.2 40.09 - 63,170.8 40

Buprenorphine 5,841 92.6% 313.0 75.1 10.01 - 58,691.5 10 Norbuprenorphine 4,237 67.2% 639.8 279.0 20 - 13,615.1 20

cTHC 11,752 100.0% 579.6 153.1 15 - 25,960.3 15

Meprobamate 13,188 99.1% 36,884.0 16,190.5 100.18 - 1,244,200 100 Carisoprodol 5,379 40.4% 2,931.9 455.0 100.1 - 648,442 100

Cocaine metabolite 4,951 100.0% 12,372.5 627.1 50.05 - 342,160 50

Table 1. Drug and Metabolite Prevalence, Positivity, and Concentrations. N = 184,049 patient

**N % Mean Median Range Cutoff Positive Positive (ng/mL) (ng/mL) (ng/mL) (ng/mL)**

are used in much lower concentrations than the earlier-designed drugs (Fraser, 2001). This complicates identification of these new agents by immunoassay.
