THC Detox Shop / Urine Drug Testing
Urine Drug TestingUrine drug test is the most common type. Urine is the specimen of choice since it contains the most metabolites of a drug taken. Urine is the main excretory route for drugs and their metabolites. The following is a summary of the analytical methods used by laboratories to detect the presence of drugs or their metabolites in the urine drug test:
Immunoassays
These drug testing procedures are most commonly used to screen samples. In the event that drugs or their metabolites are detected, then the sample is normally tested again using an even more sensitive test such as Gas Chromatography and Mass Spectometry. Immunoassays work on the principle of antigen-antibody interaction. Antibodies are chosen which will bind selectively to drugs or their metabolites. The binding is then detected using either enzymes, radioisotopes or fluorescent compounds.
EMIT (Enzyme Multiplied Immunoassay Technique) is manufactured by Syva Laboratories. It uses an enzyme as the detection mechanism. It is the cheapest, simplest to perform and the most widely used of the immunoassays. The EMIT is commonly used by employers as an initial drug testing step. The EMIT is the most commonly used test for pre-employment screenings despite having a 4-34% "false positive" rate.
RIA (Radio Immunoassay) is manufactured by Roche Diagnostics. It is similar to EMIT but uses a radioactive isotope such as iodine instead of an enzyme. However, because it involves using radioactive substances, it is less popular than EMIT. This is a highly sensitive form of drug testing mainly used by the military. Mistakes come from poor calibration. The manufacturer states that “a positive test result should be confirmed…”
FPI (Fluorescence Polarization Immunoassay) is manufactured by Abbott Laboratories. Fluorescent compounds mark the selective binding of antibodies to drugs and their metabolites. It is a highly sensitive and highly specific type of drug testing .
Chromatography
TLC (Thin Layer Chromatography)
This drug testing procedure involves the addition of a solvent to the sample causing the drugs and their metabolites to travel up a porous strip leaving color spots behind. As each different substance travels a specific distance, the strip can then be compared with known standards. This type of drug testing gives no quantitive information, it merely indicates the presence of drugs or their metabolites. Furthermore, it relies on the subjective judgment of a technician and requires considerable skill and training. False positives result from misinterpretations. It is not widely used.
GC/MS (Gas Chromatography/Mass Spectometry)
This is the most precise type of drug testing for identifying and quantifying drugs or their metabolites in the urine. The GC/MS is routinely used as a confirmation test following a positive result on an Immunoassay. It involves a two step process, whereby Gas Chromatography separates the sample into its constituent parts and Mass Spectometry identifies the exact molecular structure of the compounds. The combination of Gas Chromatography and Mass Spectometry is considered to be the definitive method of establishing the presence of drugs or their metabolites in the urine. However, the equipment necessary to perform it is extremely expensive and this is reflected in the price for drug testing each sample. Occasionally problems do arise with poor calibration of the equipment. Mistakes also commonly happen if the machine is not thoroughly cleaned – samples can be contaminated by small traces from the previous urine drug testing sample. Temperature, pressure, and storage time of samples must be rigidly controlled.
