Rapid Testing Cups Vs. Automated Chemistry Instruments

Are You Leaving the Door Open for Inaccurate Results?

Welcome to the next article in our series focusing on laboratory testing in pain management practices. This article will highlight the differences in (EIA) enzyme-immuno assay methods for rapid testing cups and automated chemistryinstruments.

Many pain management practices across the country utilize rapid testing cups as their method of performing urine drug screens to monitor medication compliance. It is important to note that rapid drug testing cups were originally developed for use in hospital emergency departments and forensic testing venues. While they are currently being marketed to pain practices, I was unable to find any data that supports that they have been modified in any way to support their use for medication monitoring in pain management practices. Rapid urine drug screening cups utilize "flow through or lateral flow" EIA methodology. Many CLIA waived tests utilize this technology and are very sensitive and specific, however, they are subject to processing errors that can effect accurate test reporting. This technology basically attaches a "target or targets" to the test membrane, the specimen being tested flows across the membrane and if the "target" is present it attaches to the membrane which results in the development of a visual read result. The sensitivity and specificity for urine drug screen cups, in my opinion as a medical technologist, is less than optimal. The reported sensitivity and specificity per the manufacturer product insert ranges from 90-98% sensitivity and 85-96% specificity. This leaves the door open to inaccurate results and when coupled with the specimen volume requirement and reading time requirement, these tests may not be producing accurate results. Additionally, the cutoffs used to determine the result vary widely between manufacturers and all of them list numerous interfering substances. All rapid test cups produce qualitative, either positive or negative test result and all manufacturers product inserts indicate the results should be confirmed. So the next step is supplemental testing. For those practices that have established a physician office laboratory, congratulations – you've already forward the specimen to your laboratory for testing. For those of you who haven't set up a physician office laboratory, you will need to send the specimens to toxicology reference laboratory. At either the POL or reference lab, the specimens are tested utilizing another form of EIA technology on an automated instrument. Many instruments utilize a "sandwich or competitive" EIA method and employ a spectrophotometric reading component.

The process basically is as follows:

  • Reagent and sample are mixed together
  • Incubated to allow reaction to occur
  • Another reagent is added to mixture
  • Color development occurs that is directly proportional to the amount of reaction that occurred
  • Specimen is read at a specific wavelength by the photometer
  • Reaction data is converted to a result number and reported

Automated instruments can be set up to report qualitative (negative or positive) results or quantitative (numerical) results. The decision on what type of reporting to be used must be made by the practice. When reporting quantitative results the testing is considered lab developed high complexity testing by CLIA therefore it must be validated to the specifications required for compliance.

Having performed thousands of instrumented urine drug screen tests and compared them to rapid cup and LC/MS results it is important to note that the rapid cups results in many (and I mean many) cases do not compare to the automated analyzer results.

With that said I caution physicians from making treatment and patient management decisions solely from rapid testing cup results. In contrast, automated instrument quantitative results when compared to LC/MS results had a 99% agreement rate.

For practices with in house labs running quantitative testing on an automated analyzer you can have confidence in your test results.

While enzyme immune assay methods can be utilized in different testing capacities, it is important to utilize the methods that are going to give you the most information and accurate test results when treating your patients.