Alternate Names: Barbiturates - screen; Benzodiazepines - screen; Amphetamines - screen; Analgesics - screen; Antidepressants - screen; Narcotics - screen; Methanol - screen; Phenothiazines - screen; Isopropanol (rubbing alcohol) - screen; Drug abuse screen; Blood alcohol test
How Performed: Toxicology screening is most often performed on blood or urine (the specimens of choice) but can be performed on gastric contents (vomit or lavage fluids) if performed soon after the substance is ingested. Nails or hair can be tested for arsenic and mercury.
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Urine sampling can be a random sample (you are asked to urinate into a container). In some circumstances, you may need to obtain the urine sample in the presence of the nurse or technician (to verify that the urine sample came from you and was not tampered with -- see special consideration).
How To Prepare: There is no special preparation; this test is often performed as an emergency test. Inform the health care provider of any prescription and over-the-counter medications you have taken, including the amount and time of ingestion.
How It Feels: When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
If a urine sample is used, it involves only normal urination and there is no discomfort.
Risks:
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Why Performed: This test can be used to evaluate possible accidental or intentional overdose or poisoning, such as when there is a need to evaluate the type and amount of legal and illegal drugs used by a person. The test can be performed to determine the cause of acute drug toxicity, to monitor drug dependency, and to determine the presence of substances in the body (for medical and/or legal purposes). See also: Drug abuse first aid.
If the test is used as a drug screen there is a finite amount of time after ingestion that the drug or any of its metabolites can be detected:
- cocaine
- amphetamines
- heroin
- morphine
- phencyclidine (PCP)
- alcohol
- benzodiazepines
- up to 6 weeks with high level use
- hydromorphone
- tetrahydrocannabinol (THC)
- 6 to 11 weeks with heavy use
- propoxyphene
- methadone
- codeine
- barbiturates
Normal Values: "Normal" levels vary according to the institution performing the test.
Blood can be tested for the presence and levels (amounts) of medications. Urine screening is usually reported as positive (substance is present) or negative (absent), but the level of certain substances can also be measured fairly accurately in urine.
Therapeutic levels are found for prescribed or over-the-counter medications (see the specific medication).
There is no alcohol, prescription medications not prescribed, or illegal drugs.
Carboxyhemoglobin: less than 3% of total hemoglobin (up to 15% in tobacco smokers)
Methemoglobin: less than 3% of total hemoglobin
Sulfhemoglobin: not detectable
Abnormal Results: The presence of illegal drugs or drugs not prescribed for the person indicates illicit drug use.
Elevated levels of alcohol or drugs can indicate intentional or accidental intoxication and/or overdose.
Carboxyhemoglobin results from the union of hemoglobin and carbon monoxide. Elevated levels may indicate carbon monoxide poisoning.
Methemoglobin results from the oxidation of ferrous iron to ferric iron. Elevated levels may indicate the use of chemicals and drugs such as aniline, chlorates, nitrates, nitrites, phenacetin, or sulfonamides, or may exist as a primary condition.
Sulfhemoglobin results from the combination of hemoglobin with certain drugs such as phenacetin or sulfonamides; it causes cyanosis (blueness of the skin) but few other symptoms.
Additional conditions under which the test may be performed:
Cost:
Special Considerations: Commonly found substances on a toxicology screen include:
- alcohol (ethanol) -- "drinking" alcohol (see Alcohol and diet)
- amphetamines
- benzodiazepines
- antidepressants
- barbiturates and hypnotics
- hemoglobin derivatives
- isopropanol -- isopropyl alcohol, rubbing alcohol (toxic) (see isopropanol overdose)
- methanol -- methyl alcohol, found in antifreeze and other substances (toxic)
- narcotics
- non-narcotic analgesics
- acetaminophen - oral
- anti-inflammatory analgesics - oral
- phenothiazines (antipsychotic or tranquilizing medications)
- prescription medications, any type
This test is sometimes part of an investigation for drug use or abuse; special consents, handling and labeling of specimens, or other special procedures may be required.
