Enzyme multiplied immunoassay technique

Enzyme multiplied immunoassay technique (EMIT) is a common method for qualitative and quantitative determination of therapeutic and recreational drugs and certain proteins in serum and urine.

Enzyme multiplied immunoassay technique
Other namesEMIT
MeSHD017248

It is an immunoassay in which a drug or metabolite in the sample competes with an drug/metabolite labelled with an enzyme, to bind to an antibody. The more drug there is in the sample, the more free enzyme there will be, and the increased enzyme activity causes a change in color.[1]:70

Determination of drug levels in serum is particularly important when the difference in the concentrations needed to produce a therapeutic effect and adverse side reactions is small, the therapeutic window. EMIT therapeutic drug monitoring tests provide accurate information about the concentration of such drugs such as immunosuppressant drugs and some antibiotics.[2][3]

EMIT urine assays for drugs such as cannabinoids, morphine, and amphetamine are designed to detect the drug itself or a metabolite of the drug present in a concentration above a pre-specified minimum detection cutoff limit.[4] In the U.S., the cutoff limits must be set in accordance with Mandatory Guidelines for Federal Workplace Drug Testing Programs that were developed by SAMHSA (The Substance Abuse and Mental Health Services Administration is a branch of the U.S. Department of Health and Human Services). The setting of reasonable cutoff limits help reduce false positive results that occur from assay limitations. Because of the social and legal consequences, a positive test result must be confirmed by an alternative method, usually Gas Chromatography/Mass spectrometry. As an example the SAMHSA cutoffs for cannabinoids are 50 ng/ml for the immunoassay and 15 ng/ml as confirmed by GC/MS.[5] Immunoassays that do not conform with SAMHSA, featuring a cutoff of 20 ng/ml, have been shown to produce false positives from passive inhalation of marijuana smoke.[6]

See also

References
  1. "Clinical Drug Testing in Primary Care - Technical Assistance Publication Series TAP 32" (PDF). Substance Abuse and Mental Health Services Administration. 2012.
  2. Johnston, A; Holt, DW (2001). "Immunosuppressant drugs--the role of therapeutic drug monitoring". British Journal of Clinical Pharmacology. 52 Suppl 1: 61S–73S. doi:10.1111/j.1365-2125.2001.00365.x. PMC 2014623. PMID 11564054.
  3. Begg, EJ; Barclay, ML; Kirkpatrick, CM (2001). "The therapeutic monitoring of antimicrobial agents". British Journal of Clinical Pharmacology. 52 Suppl 1: 35S–43S. doi:10.1111/j.1365-2125.2001.00377.x. PMC 2014626. PMID 11564051.
  4. "Test Method-Screening - EMIT" (PDF). Washington State Patrol Toxicology Laboratory. March 16, 2016.
  5. http://www.gpo.gov/fdsys/pkg/FR-2010-08-16/pdf/2010-20095.pdf%5B%5D
  6. Cone, E. J.; Bigelow, G. E.; Herrmann, E. S.; Mitchell, J. M.; Lodico, C.; Flegel, R.; Vandrey, R. (2014). "Non-Smoker Exposure to Secondhand Cannabis Smoke. I. Urine Screening and Confirmation Results". Journal of Analytical Toxicology. 39 (1): 1–12. doi:10.1093/jat/bku116. PMC 4342697. PMID 25326203.

Further reading
  • "The Immunoassay Handbook", 4th Edition, David Wild, Ed., Elsevier,2013, p 76
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