Labs Performing UDT
Many laboratories performing UDT on the pain patient population typically test specimens by immunoassay and then follow this with confirmation by mass spectrometry (Cone et al., 2008). Mass spectrometry is an analytical technique that separates molecules based on their weight (mass) and fragmentation pattern. Identification is based on the fact that each drug has a specific mass and breakdown in the same way that each person has a specific fingerprint. A mass spectrometry instrument is usually coupled to a chromatographic column, in which the test drug, for example morphine, is separated from other components in the urine before submitting the sample into the mass spectrometer. The mass spectrometer identifies the test drug by its position in the chromatogram, the specific weight of the molecule, and by its fragmentation pattern. This technology is virtually foolproof. Mass spectrometry techniques are divided into two methods: gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Of the two, the newer LC-MS/MS is considered the gold standard, for reasons we will describe later (Siuzdak, 2006). In cases where the physician wants the results immediately (within hours), confirmatory mass-spectrometry methods used at the most modern diagnostic laboratories provide results within 24-30 hours. As stated above, the major limitations of immunoassays are inappropriate cutoffs (sensitivity), varying specificity for individual drugs, and cross-reactivity with other agents producing both false-negative and false-positive results.
Amadeo Pesce, Cameron West, Kathy Egan-City and William Clarke (2012). Diagnostic Accuracy and Interpretation of Urine Drug Testing for Pain Patients: An Evidence-Based Approach, Toxicity and Drug Testing, Prof. Bill Acree (Ed.), ISBN: 978-953-51-0004-1, InTech,