Confirmation Testing Q&A (part 1)
Dr. Joseph E. Graas, Scientific Director
Dr. Edward Moore, Medical Director
What is a confirmation test?
A confirmation test is a secondary test method used by a laboratory to verify the results of an initial drug screen. Whereas a screen tests at the class level, a confirmation test identifies the specific analytes (drugs) present in a patient’s system.
How is a confirmation test different than a screen?
A test by a Chromatographic method (TLC, GC/MS or LC/MS) is generally considered to be a Confirmation. Confirmation tests use completely different testing methodologies and different technologies than those used for a drug screen (immunoassay or radioimmunoassay RIA). Confirmations are more labor-intensive than a screen. A screen typically will utilize higher cutoff levels as it is looking for more broad information, whereas a confirmation test will use lower cutoff levels as it is looking for more specific information to identify and quantify the target analyte.
Specifically, what does a confirmation test reveal?
Confirmations: 1) are a verification of the initial immunoassay test results; 2) determine which specific analytes are responsible for causing positive results; 3) reveal how much of each analyte is present in the patient’s urine/saliva sample; and 4) identify if the screen test positive was due to illicit drug use or a medication interaction.
Why have a confirmation test performed? When is it appropriate?
In most cases, a confirmation test is performed when the screening results are not consistent with the patient’s medications or a patient contests the results of their drug screen. A confirmation test can also reveal whether a positive screen is the result of a patient taking a medication that they are being prescribed or from an illicit substance (or both). For example, a sample that confirms positive for alprazolam (Xanax) rejects a patient’s claim that their sample screened positive for the benzodiazepines class due to a prescription for Valium (diazepam).
What are the different types of confirmation methodologies?
The most common types of confirmation are Thin-Layer Chromatography (TLC), Gas Chromatography Mass Spectrometry (GC/MS) and Liquid Chromatography Mass Spectrometry (LC/MS/MS).
How are they different?
Besides each type of confirmation test using its own specific technology, each has its own “pros” and “cons” depending upon a program’s needs and the purpose for the drug-testing (see below table). For example, a TLC confirmation can only be used on a urine sample and thus is not an option for a program that only collects saliva from their patients; GC/MS and LC/MS/MS can be performed on both urine and saliva samples.