Methods of UDT

Urine Drug Test Method Comparison Table

Comparing Immunoassay to GC/LC-MS

 ImmunoassayGC/LC-MS
Drug Detection WindowMultiple daysUsually 1-2 days
Cross Reacting Compounds (False Positives)Cross reactions can occurAlmost never a concern
Identifying drugs within a similar classCannot always differentiate (ie MOP positive from codeine, morphine and heroin)Can identify between specific drugs from same class
CostCheapExpensive
Time of Test5 minutes after sample collection - point of care testHours to days after sample collection - dependant on lab

There are two main types of urine drug tests - immunoassay (point-of-care, "presumptive" testing), and chromatography mass-spectrometry (lab-based, "confirmatory" testing). Below is an explanation of each.

Urine Drug Testing Immunoassay

Immunoassays are inexpensive tests that give you quick information in a point-of-care setting

Immunoassay kits and strips have made urine drug testing (UDT) extremely easy to do. The disposable kits can be used by clinicians in any setting making them invaluable for primary care physicians. The HARMS Program is all about using UDT to risk stratify patients for addiction risk since UDT is one of the only methods for collecting objective information about a patient's drug use. Immunoassay kits will usually come with a series of 5 or 6 panels that detect drug classes that are relevant to you such as opiates, synthetic opioids, benzodiazepines and cocaine. These panels can give a heap of information in 5 minutes from urine sample collection.

The panels that are present on a single kit can be tailored by the user to meet their specific needs but limitations of each panel should be understood beforehand. For example the opiate and morphine panels are extremely sensitive to morphine, codeine and heroin but are not very sensitive to semi-synthetic opioids like oxycodone or buprenorphine. If you would like to detect these compounds reliably then specific immunoassay panels for semi-synthetic and synthetic opioids should be utilised.

After selecting the appropriate panels and understanding their limitations one should always consider the detection limit of each panel, common false positives that may cross-react with the immunoassay and any signs of tampering done by the patient to alter results. Sometimes interpreting these results can be challenging and that is why the START-IT Tool was created to assist physicians with the interpretation of urine drug immunoassays. If the immunoassay does not give clear results or you require further information than it recommended that a follow-up test occur or you order chromatography-mass spectrometry to obtain further information.

How an Urine Drug Immunoassay Works

This video explains the basic science behind how an urine drug immunoassay works. This information is for further understanding and is not required to perform an urine drug test.

 

Example of a point-of-care urine drug immunoassay panel.

 

Chromatography Mass-Spectrometry

Highly accurate tests that can differentiate between metabolites and drugs that immunoassays cannot

Gas/Liquid Chromatography - Mass Spectrometry is used when you want to confirm the results obtained by an immunoassay or when the immunoassay does not possess the ability to detect a particular compound. A prime example of this is when the opiate or morphine panels are positive which can indicate the patient is using morphine, codeine or heroin. It is impossible to know which of these drugs are causing the positive result on an immunoassay so chromatography and mass spectrometry is required to find out which drugs are in the urine.

Since this method is so accurate, false positives do not have to be considered. This is useful for when you suspect a positive result for immunoassay to be from a cross reaction with a different drug the patient is using. Although chromatography-mass spectometry is highly accurate, its sensitivity suffers compared to immunoassay meaning the detection limit is reduced.

Like most laboratory tests, chromatography-mass spectrometry times will vary depending on the laboratory available to you so wait time for these results can be on the scale of days rather than minutes for immunoassay. These tests can also be quite a bit more expensive than the immunoassays meaning these tests should only be used when the immunoassay results are insufficient on their own.

How Gas/Liquid Chromatography - Mass Spectrometry Works

This video explains the basic science behind how gas/liquid chromatography - mass spectrometry works. This information is for further understanding and is not required to perform an urine drug test.