Enzyme Multiplied Immunoassay Technique
Encyclopedia
Enzyme multiplied immunoassay technique, or EMIT, is a common method for screening urine
and blood
for drugs
, both legal or illicit. First introduced by Syva Company in 1973, it is the first homogeneous immunoassay to be widely used commercially.
A mix and read protocol has been developed that is exceptionally simple and rapid. The most widely used applications for EMIT are for therapeutic drug monitoring (serum) and as a primary screen for abused drugs and their metabolites (urine). The US patents covering the major aspects of the method, 3,817,837 and 3,875,011, have expired. While still sold by Siemens Healthcare under its original trade name, EMIT, assay kits with different names that employ the same technology are supplied by other companies. The test is not particularly accurate, especially with regard to test results for cannabis
. When the Food and Drug Administration
approved EMIT, it did so with the strict provision that positive test results should be confirmed by an alternative testing method.
2) Allow binding of Ag & Ab (incubation #1).
3) Add a known concentration of prepared Ag-enzyme conjugate.
4) Allow binding of Ag-enzyme conjugate with any remaining unbound Ab in solution (incubation #2).
The conjugate is constitutionally active; binding to any unbound Ab will render it inactive.
5) Add enzyme substrate.
6) Measure enzyme activity.
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
and blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
for drugs
Psychoactive drug
A psychoactive drug, psychopharmaceutical, or psychotropic is a chemical substance that crosses the blood–brain barrier and acts primarily upon the central nervous system where it affects brain function, resulting in changes in perception, mood, consciousness, cognition, and behavior...
, both legal or illicit. First introduced by Syva Company in 1973, it is the first homogeneous immunoassay to be widely used commercially.
A mix and read protocol has been developed that is exceptionally simple and rapid. The most widely used applications for EMIT are for therapeutic drug monitoring (serum) and as a primary screen for abused drugs and their metabolites (urine). The US patents covering the major aspects of the method, 3,817,837 and 3,875,011, have expired. While still sold by Siemens Healthcare under its original trade name, EMIT, assay kits with different names that employ the same technology are supplied by other companies. The test is not particularly accurate, especially with regard to test results for cannabis
Cannabis (drug)
Cannabis, also known as marijuana among many other names, refers to any number of preparations of the Cannabis plant intended for use as a psychoactive drug or for medicinal purposes. The English term marijuana comes from the Mexican Spanish word marihuana...
. When the Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
approved EMIT, it did so with the strict provision that positive test results should be confirmed by an alternative testing method.
Technique
1) Combine a sample containing an unknown concentration of antigen (Ag) & a solution containing a known concentration of antibody against the Ag (Ab).2) Allow binding of Ag & Ab (incubation #1).
3) Add a known concentration of prepared Ag-enzyme conjugate.
4) Allow binding of Ag-enzyme conjugate with any remaining unbound Ab in solution (incubation #2).
The conjugate is constitutionally active; binding to any unbound Ab will render it inactive.
5) Add enzyme substrate.
6) Measure enzyme activity.