ELISA is a sensitive and specific method but it is not as easy to automate as CEDIA or EMIT assays. EMIT and CEDIA methods are faster and higher-throughput methods and so are now more common in routine drug testing.
Radioimmunoassays (RIA) were one of the earliest immunoassays developed for drug testing, and while very sensitive, they are no longer widely used because of the costs involved with using radioactive isotopes and generating radioactive waste.
It is important to note that immunoassays do not give quantitative results. Rather, qualitative results of classes of drugs or metabolites are obtained. A simple 'positive' or 'negative' result is reported using a cutoff concentration; above which an analyte is reported as present or positive and below which it is reported as absent or negative.
Note: Not all drugs can bind antibodies and thus be detected by immunoassays. Some examples are ethanol/other alcohols and ethyl sulfate. These compounds are too small to be measured with immunoassays.
