Many tests are in use for detecting the drugs in the system. There are some instant test which are easy and convenient to use and there are some laboratory tests which are a bit complicated but proven effective to find even very minute amounts of drugs present in the specimen. Among them, immunoassay is one of the useful tests which helps in finding even the small quantities of illicit drugs.
An immunoassay is a biochemical test that measures the presence or the concentration of the substances in the given solutions or specimens. The specimens are something like the urine or saliva which are frequently used to do the regular drug tests. The analysis of these things are based on the unique ability of an antibody to bind with high specificity to one or a very limited group of molecules. A molecule that binds to an antibody is called an antigen.
Immunoassay tests use the antigen antibody interactions to detect illegal substances in the body. These antibodies bind selectively to certain drugs and the sensitivity and the specificity of the drug will be determined. And these components of the test are as good as the antibody chosen. If the binding is proportional to the amount of the drug in the urine then it can be detected through enzymes, radioisotopes or florescent compounds.
Using this technique, very small amounts of drug can also be detected in a very small amount of urine. However this drug cannot differentiate the specific drug within the class of drugs. Most of the tests conducted using this method are 97-99% accurate and false negatives are more common than false positives.