The Screen Threshold and Confirm Threshold are the standard cutoff levels that the laboratory uses when testing a specimen.
When the laboratory first receives the specimen, they run the Immunoassay test or Screen test. Immunoassays use antibodies to detect the presence of a drug or metabolite in the urine. Antibodies are proteins that chemically bind with specific substances called antigens; in this case, a drug or drug metabolite. The first column of numbers on the NTA test results under Screen Threshold are the quantitative cutoff levels for this test.
The primary disadvantage of immunoassays is that the antibodies are seldom specific to a single drug or drug metabolite; therefore, the antibodies may bind with other substances. This is called cross-reactivity and can result in false positives. Because of this, if a substance shows positive (or above the screen threshold), the specimen is sent on for the GC/MS (Gas Chromatography/Mass Spectrometry) test, or Confirmation Test. The second column of numbers on the NTA, Inc. test under Confirm Threshold are the quantitative cutoff levels for this test.
The GC/MS test is a very sensitive and specific test, and the procedures for performing this test are very complex. In short, however, this test separates and very specifically identifies the components of the specimen, making it a highly reliable test for confirmations.
The Screen and Confirm Thresholds on the NTA, Inc. results are simply the cutoff levels for each substance on each particular test. They have nothing to do with one another, and do not reflect levels that are found in a specimen.