Chemistry Laboratory 5

The common groups of drugs screened for in urine
are Cocaine, marijuana, methamphetamine, and opiates.
Monoclonal antibodies are used
in the test lines for each drug along with the corresponding drug-protein conjugate. If the drug is present in the urine above its cut off concentration it will saturate all binding sites of the monoclonal antibody and prevent the antibody from reacting with the drug-protein conjugate resulting in no visible line.
The cut-off concentration
is the concentration at which presence of the drug in the urine is not indicative of drug abuse. If the concentration of the drug is lower then the cut-off concentration, then the drug is being abused, if the concentration is higher than that of the cut-off concentration then further testing is needed to determine the possibility of drug abuse.
The limitations associated with screening for drugs of abuse
are that for legal reasons a secondary method (GC/MS) is needed to confirm a result, procedural errors, bleach or adulterants which produce erroneous results, results are not quantitative, negative does not mean drug free, test does not differentiate between medications and drugs of abuse, and a positive test can result due to certain foods or supplements.
Screening for drugs of abuse is a point-of-care test
in that the testing is brought right to the patient and the results are rapid.
What does a positive test indicate?
positive test indicates that the drug is present in the urine sample at a lvel above it’s cut-off concentration
Is a positive result always determined by the presence of the primary drug?
positive results can be from substances that saturate binding sites of the antibody like bleach, adulterants, medications, and food. Some tests also test for metabolites in addition to the drug
Explain the principle of the cartridge test?
immunoassay based on mechanisms of competitive binding. the drug in the urine competes with the drug conjugate for binding sites on the antibody. The test line has a MaB and the drug conjugates. the drug saturates the binding sites on the antibody and no line will be present. a negative has a line

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