Lab Screening & Confirmation: What’s the Difference?

Screening

Screening refers to a preliminary test that yields a positive or negative result. It can be done with a rapid test or by using laboratory instrumentation such as enzyme-linked immunosorbent assay (EIA) or enzyme multiplied immunoassay technique (EMIT).

EMIT is the cheapest and most used workplace drug test. Both rapid tests and lab screens use the same testing technology, called immunoassay technology. However, these tests are prone to incorrect results because the screening technology is non-specific, meaning that it does not differentiate among drug classes.

An example of a result is that of a positive opiate result, which only indicates that there is some opiate present. This could be a doctor prescribed medication like hydrocodone (Vicodin) or codeine (Tylenol 3) or it could be an illegal drug like heroin. Unfortunately, some companies may not ask for a prescription list to rule out legally used meds and not hire based on a general positive result.

Confirmation

Confirmation testing is much more accurate than screenings are. Their utilization of high complexity instrumentation yields a definite and specific result. Best practice for confirmation testing involves using either a gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry.

The results of a confirmation test provide a definite result that indicates the specific drug or compound present in the urine or oral fluid sample. Though not as cheap as a screening, LC-MS/MS confirmation testing should be considered the standard in many cases because the results are precise, accurate, and court admissible.

Re-Screening

Best practice confirmation protocol involves all positive screens to be confirmed using mass spectrometry. Many labs protocol includes re-screening all samples that come into the lab for confirmation testing prior to specimen going on the mass spec. There are several disadvantages to this protocol.

Many samples arriving for confirmation testing have already been through rapid/onsite testing devices, yielding a preliminary and qualitative positive result. Keeping the sample for re-screening instead of it going straight onto the GC/MS or LC-MS/MS can delay turnaround time. The re-screen on the laboratory EMIT or EIA does not provide any new information and will result in the same answers that testing already conducted with the rapid/onsite (POCT) device found.

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