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Types of Screens Being Used To Test For Drugs


This is the most widely used test by employers because of its low cost. More than 95% of employers use this as an initial test. Manufactured by the Syva company, its accuracy is so suspect that the company itself recommends a more refined GC-MS test to confirm positive results. Because many employers don’t want to spend the $100 to $150 dollars charged for the GC-MS, employees have been fired on the results of the EMIT test alone. Courts have ruled that repetition of the EMIT test does not constitute confirmation of a positive drug finding.

This test does not measure drugs in the urine directly. Rather, a reagent is added to the urine sample to bind with the metabolite of the drug being searched for. Then a second reagent is added to decrease the enzyme activity of the first. The result is read by a light sensing instrument measures the photometric spectrum. The problem is reagents combine with substances similar to drug metabolites. Hence Advil, Sinex or other medicines may be similar enough to certain illegal drugs to cause a positive reaction.


This test is somewhat more sophisticated and more expensive than the EMIT test. Produced by Roche Diagnostics Inc. under the name Abuscreen, this test is occasionally used by the armed forces. This more complicated procedure involves adding a radioactive antigen to the sample of urine and analyzing it by a machine. Mistakes come from poor calibration. The manufacturer states “a positive test result should be confirmed by a GC / MS”


This stands for thin layer chromatography. The procedure involves adding solvent to urine to extract drugs and then comparing color spots on a TLC plate to that of a standard. TLC relies on the subjective judgment of a technician and requires considerable skill and training. False positives result from misinterpretations. It is not widely used.


Gas Chromatography-Mass Spectrometry. In this, the most sophisticated test a sample of urine is injected into the machine. The urine separates as it travels from the injection port to the detector and as the sample emerges from the gas chromatograph and is ionized by electron bombardment. The resulting positive ion mass fragments are read by the mass spectrometer. The results are produced on a computer print out.

While in theory the GC-MS test is excellent, in practice, errors creep in. Temperature, pressure, and storage time of samples must be rigidly controlled. Expensive environmental controls and immaculate cleaning practices must be observed. Too often, commercial labs have an economic incentive to rush testing, cleaning and maintenance. Mistakes most commonly happen when the highly sensitive machine is not thoroughly cleaned. Your sample could easily be contaminated by small traces from the previous urine sample.

Bobby Gladd a respected laboratory quality assurance analyst reports documentation of false reports of GC-MS tests in the environmental field. Researcher Gladd believes that many results could be challenged in court for faulty procedure. For those considering a legal challenge to false reports, Gladd’s firm might be for hire.

Hair & Saliva Tests

Hair tests have received considerable publicity. In theory a snippet of hair near the nap of your neck could indicate illegal drug usage for the last several months. The accuracy of these tests has not been determined. The cost of hair tests and saliva tests have been prohibitive. Because employers are sticking with the inexpensive EMIT test, these tests have not been adopted and are not a matter of concern at the present.

Posted by A. Shapiro
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