American Association for Clinical Chemistry
Improving healthcare through laboratory medicine
Eliminating False Positive And False Negative Results In The Toxicology Laboratory

September 8, 2004

Amitava Dasgupta, PhD

Clinical drug testing can vary from a simple test for blood ethanol plus a urine screen for selected drugs using disposable detection kits to a complex drug panel requiring several technologies. For example, some testing protocols may require a urine or gastric screen by combinations of automated immunoassays, colorimetric spot tests, thin-layer chromatography (TLC), gas chromatography (GC), high performance liquid chromatography (HPLC), and/or gas chromatography/mass spectrometry (GC/MS) with quantitation of all drugs in blood or serum.

Today, immunoassays for drugs of abuse are available on automated analyzers and as point-of-care assays that can be read visually, thereby allowing laboratories of any size to perform drug screening on an emergency basis. Workplace drug testing regulations require GC/MS confirmation of samples testing positive by immunoassay, so-called presumptive positives.

This month, Amitava Dasgupta, PhD (DABCC) professor of pathology and laboratory medicine at the University of Texas-Houston, will offer some tips on “ELIMINATING FALSE POSITIVE AND FALSE NEGATIVE RESULTS IN THE TOXICOLOGY LABORATORY.” Join us as Dr. Dasgupta reviews:

  • Tests to detect adulteration in urine submitted for drugs of abuse testing.
  • True positive drug tests
  • Interference in serum digoxin assay due to endogenous DLIS and drugs.
  • Drug metabolites and immunoassays.