A toxicology screen refers to various tests to determine the type and approximate amount of legal and illegal drugs a person has taken.
Barbiturates - screen; Benzodiazepines - screen; Amphetamines - screen; Analgesics - screen; Antidepressants - screen; Narcotics - screen; Phenothiazines - screen; Drug abuse screen; Blood alcohol test
How the test is performed
Toxicology screening is most often done using a blood or urine sample. However, it may be done soon after swallowing the medication, using stomach contents that are obtained through gastric lavage or after vomiting.
How to prepare for the test
No special preparation is needed. If able, tell your health care provider what drugs (including over-the-counter medications) you have taken, including when and how much.
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.
How the test will feel
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.
A urine test involves normal urination. There is no discomfort.
Why the test is performed
This test is often done in emergency medical situations. It can be used to evaluate possible accidental or intentional overdose or poisoning. It may help determine the cause of acute drug toxicity, to monitor drug dependency, and to determine the presence of substances in the body for medical or legal purposes.
Additional reasons the test may be performed:
- Alcohol withdrawal state
- Altered mental state
- Analgesic nephropathy (kidney poisoning)
- Complicated alcohol abstinence (delirium tremens)
- Drug abuse monitoring
- Fetal alcohol syndrome
- Intentional overdose
- Stroke secondary to cocaine
- Suspected sexual assault
If the test is used as a drug screen, it must be done during a certain time period after the drug has been taken or while forms of the drug can still be detected in the body. Examples are below:
- Alcohol: 3 to 10 hours
- Amphetamines: 24 to 48 hours
- Barbiturates: up to 6 weeks
- Benzodiazepines: up to 6 weeks with high level use
- Cocaine: 2 to 4 days; up to 10 to 22 days with heavy use
- Codeine: 1 to 2 days
- Heroin: 1 to 2 days
- Hydromorphone: 1 to 2 days
- Methadone: 2 to 3 days
- Morphine: 1 to 2 days
- Phencyclidine (PCP): 1 to 8 days
- Propoxyphene: 6 to 48 hours
- Tetrahydrocannabinol (THC): 6 to 11 weeks with heavy use
Normal value ranges for over-the-counter or prescription medications may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
A negative value usually means that alcohol, prescription medications that have not been prescribed, and illegal drugs have not been detected.
A blood toxicology screen can determine the presence and level (amount) of a drug in your body.
Urine sample results are usually reported as positive (substance is found) or negative (no substance is found).
What abnormal results mean
Elevated levels of alcohol or prescription drugs can be a sign of intentional or accidental intoxication or overdose.
The presence of illegal drugs or drugs not prescribed for the person indicates illicit drug use.
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Substances that may be detected on a toxicology screen include:
- Alcohol (ethanol) -- "drinking" alcohol
- Barbiturates and hypnotics
- Flunitrazepam (Rohypnol)
- Gamma hydroxybutyrate (GHB)
- Non-narcotic pain medicines including acetaminophen and anti-inflammatory drugs
- Phenothiazines (antipsychotic or tranquilizing medications)
- Prescription medications, any type
Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM. Toxicology and pharmacology. In: Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM, eds. Emergency Medicine: A Comprehensive Study Guide. 6th ed. Columbus, OH: McGraw-Hill; 2006:section 14.
McPherson RA, Pincus MR. Toxicology and therapeutic drug monitoring. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 23.
Sachs C, Wheeler M. Examination of the sexual assault victim. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine. 5th ed. Philadelphia, Pa: Saunders Elsevier; 2009:chap 58.