Drug Tests Health Article

Definition

Drug tests are analytical procedures that may be performed on blood, urine, or gastric fluid for the purpose of identifying an unknown drug or measuring the concentration of a specific drug.

Purpose

Drug tests are usually performed for three reasons. 1) To identify an abuse drug. The majority of drug abuse involves one or more of the following substances and these comprise a typical drug of abuse panel: amphetamines, cannabinoids, cocaine, ethanol, opiates (morphine and codeine compounds), and phencyclidine (PCP). Over 85% of drug abuse cases involve those drugs or one of the following: barbiturates, benzodiazepines, methadone, propoxyhene, LSD, methaqualone, and anti-depressants. 2) To identify a drug which may have been ingested or administered in a toxic or lethal dose either accidentally or on purpose. In addition to poisons such as pesticides and heavy metals such as arsenic, drugs are often implicated in accidental overdose and suicide situations. The three most commonly encountered drugs seen in overdose situations are ethanol, salicylate (aspirin), and acetaminophen. 3) To determine whether the amount of a drug in the blood is within therapeutic limits. This process, called therapeutic drug monitoring (TDM), is used to insure that the dose and dose interval of the drug are sufficient to maintain a therapeutic blood concentration throughout drug therapy without risk of toxicity. TDM is also performed to verify that a patient is complying with the physician's orders.

Drug abuse testing

Drug screening may be performed on urine, blood serum or plasma, or gastric fluid, but urine is the sample of choice for symptomatic cases because drugs and their metabolites concentrate in the urine. Clinical or emergency department settings require the use of a screening method because the identity of the drug is not usually known. Drug screening methods may be designed to detect a class of related drugs. For example, a drug test for amphetamines may detect methamphetamine, dexamphetamine, methylenedeoxymethamphetamine (Ectasy), and phenylpropanolamine. The latter drug is a decongestant that sometimes cross reacts with the antibodies used in the amphetamine assay (analysis). Although drug screening may be sufficient to treat the patient, medicolegal implications are usually involved and this necessitates the need for positive sample identification and confirmatory drug testing. The confirmatory test need not be more specific than the screening test, but must utilize a different method of detection. This obviates the chance of a false positive test result caused by an interfering substance unless the interferent affects both methods. Drug screening programs are also used in occupational settings as a condition of employment, and extensively by the criminal justice system for criminal investigations and monitoring persons who have been convicted of drug related offenses. These situations require stringent adherence to procedures for documenting chain-of-custody of the specimen and confirmatory testing. Federal drug testing worksites must follow the Department of Transportation (DOT) chain-of-custody procedures for collection and transport of urine samples for drug testing. Labor-atories certified by the U.S. Substance Abuse and Mental Health Services Administration (SAMHSA) must use the gas chromatography with mass spectroscopy (GC-MS) method to confirm a positive drug screening test. This method is the gold standard for drug identification because it determines the mass spectrum of the drug which is a fingerprint of its chemical composition.

Specimen collection and transport

Urine specimens should be collected in a room with separate areas for workspace and toilet. The sink should be located in the workspace area. The patient or client must be positively identified via two forms of photoidentification or a passport. A form such as a DOT Custody Control Form should be used for chain-of-custody documentation. This form should include labels for the collection bottle and bag, and signature lines for all persons who will receive the specimen. At minimum the client must be observed entering and leaving the toilet area and should be instructed to remove outer garments and empty his or her pockets. The toilet should contain a bluing agent and the client should be instructed not to flush the toilet. The collection container should be unwrapped in the client's presence and affixed with a temperature measuring strip. The sample should be examined by the collector for adulteration and rejected if not within perscribed limits for volume (at least 30 mL) and temperature (90-100°F). An acceptable sample is labeled across the lid and side so the seal will be broken if the lid is removed. The laboratory should perform a test for urinary creatinine, pH, or specific gravity to check specimen integrity.

Blood samples are collected by venipuncture using standard precautions for reducing exposure to blood-borne pathogens. It is not necessary to restrict fluids or food prior to collection. Blood should be collected in tubes containing no additive. Risks of venipuncture include bruising of the skin or bleeding into the skin.