Urine
analysis is primarily used because of its low cost. Urine drug testing is one
of the most common testing methods used. The enzyme-multiplied immune test is
the most frequently used urinalysis. Complaints have been made about the
relatively high rates of false positives using this test.
Urine
drug tests screen the urine for the presence of a parent drug or its
metabolites. The level of drug or its metabolites is not predictive of when the
drug was taken or how much the patient used. Rather, it is simply a
confirmatory report indicating the presence of the parent drug or its
metabolites.
Urine
drug testing is an immunoassay based on the principle of competitive binding.
Drugs which may be present in the urine specimen compete against their
respective drug conjugate for binding sites on their specific antibody. During
testing, a urine specimen migrates upward by capillary action. A drug, if
present in the urine specimen below its cut-off concentration, will not
saturate the binding sites of its specific antibody. The antibody will then
react with the drug-protein conjugate and a visible colored line will show up
in the test line region of the specific drug strip The synthetic urine.
When
an employer requests a drug test from an employee, or a physician requests a
drug test from a patient, the employee or patient is typically instructed to go
to a collection site or their home. The urine sample goes through a specified
'chain of custody' to ensure that it is not tampered with or invalidated
through lab or employee error. The patient or employee’s urine is collected at
a remote location in a specially designed secure cup, sealed with
tamper-resistant tape, and sent to a testing laboratory to be screened for
drugs (typically the Substance Abuse and Mental Health Services Administration
5 panel). The first step at the testing site is to split the urine into two
aliquots. One aliquot is first screened for drugs using an analyzer that performs
immunoassay as the initial screen.
To ensure the specimen integrity and
detecting possible adulterant, some other parameters such as, urine creatinine,
pH, and specific gravity are tested along in this initial test. If the urine
screen is positive then another aliquot of the sample is used to confirm the
findings by gas chromatography-mass spectrometry (GC-MS) or liquid
chromatography-mass spectrometry methodology. If requested by the physician or
employer, certain drugs are screened for individually; these are generally
drugs part of a chemical class that are, for one of many reasons, considered
more abuse-prone or of concern. For instance, oxycodone and diamorphine may be
tested, both sedative analgesics. If such a test is not requested specifically,
the more general test (in the preceding case, the test for opiates) will detect
the drugs, but the employer or physician will not have the benefit of the
identity of the drug.
