Immunoassay Rapid Test Methods
Frequently Asked Questions

Drug Tests

Drug tests is used to describe a category of test devices and methods for detecting drugs of abuse, Marijuana (THC), Cocaine/Benzcyieeqonine (COC), Amphetamine (AMP), Methamphetamine (MET), phencyclidine (PCP), Opiates (OPI), Buprenorphine (BUP), Ketamine (KTM), Benzodiazepines (BZD) and some other controlled substances.

Drug Test methods include immunoassay methods, TLC, GC/MS or LC/MS analysis methods. Drug tests based on immunoassay methods are usually for pre-screening test of drug use and GC/MS or LC/MS methods are usually for confirmation test of urine specimens showed positive results in screening test.

What is test Cut-off/cutoff?

A cut off, or cut-off, of a qualitative test method is the threshold level of the target substance that distinguishes positive and negative results. For example, if a urine amphetamine test has a cut off of 1000ng/ml, samples contain less than 1000ng/ml amphetamine should test negative and samples contain more than 1000ng/ml amphetamine should test positive. Our drug test pages list cut-off levels of each drug test.

How is cut-off level related to test accuracy?

Since the actual cut off of a test is determined by the test components (reagents and procedure), the cut off levels vary from manufacture to manufacture, and, often, batch to batch. Inaccuracy of cut off level is a major cause of systematic error in rapid immunoassay tests. For example, if an amphetamine test kit claims having a cut off level of 1000ng/ml, but its actual cut off is 1500ng/ml, a urine sample containing 1000ng/ml of amphetamine will test negative, or false negative.

Immunoassay and Rapid Test Methods

Rapid test products are based on immunoassay, a type of a assay method based on the binding reaction between antibodies and antigens. Usually an analyte or a substance to be tested is an antigen. An antibody is a special molecule produced by human or animal immune cells. Well selected antibodies bind antigens with high specificity. For example, a cocaine antibody binds with cocaine molecule only; it does not cross-bind with morphine or other substances.Varied immunoassay products have been developed by combining detectable label technology and antibody-antigen binding properties.

Rapid test is a lateral flow type of immunoassay used in rapid drug test, or drug screen test. The immunoassay reagents are embedded at different sections of a porous test strip. When a liquid sample is introduced to a sample zone of the strip (usually at one end of the strip), the sample wicks towards the opposite end of the strip, which results in the sample solution mixes wih the assay reagents and the analyte reacts with the reagents. At the end, a colour band of the colour labeled reagent will be present or absent at a middle section of the assay strip, which indicates the presence or absence of the analyte in the sample solution.