Living with Chronic Pain

Types of Urine Screenings


A urine screening is used to detect drugs in the body by collecting the urine that is produced from the kidneys. The kidneys filter toxins and certain waste products.

Two types of urine screenings are currently used -- immunoassay and gas chromatography/mass spectrometry (GC/MS). An immunoassay urine screening is cost effective and the results are obtained quickly. However, this particular screening does not detect all opioids and occasionally provides false positives. A false positive is when a test comes back positive for opioids, but no opioids were used.

Immunoassay is the most common type of urine screening, but it fails to measure the actual amount of opioids in the body. Instead, it detects the drug interaction with the body's immune system. Results of this test are expressed in ng/ml (nanograms per milliliter) form. Problems arise when instant immunoassay tests fail to display the ng/ml measurement; however, a test strip, that turns a certain color if drugs are present, can be used. If an immunoassay comes back positive, a gas chromatography/mass spectrometry is done for concrete confirmation that drugs are in the system. This screening is much more accurate but also more costly, and the results take much longer. Unfortunately, both of these types of screenings can provide a false negative result (indicating no drugs are in the system when drugs are being used), and both can fail to denote same-day drug use.

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