Toxicology screen

Alternative 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

These are various tests to evaluate the type (and roughly measure the amount) of legal and illegal drugs a person has taken.

How the test is 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.

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to 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 band 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 considerations).

How to prepare for the test
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 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.

If a urine sample is used, it involves only normal urination and there is no discomfort.

Why the test is 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       o 2 to 4 days; up to 10 to 22 days with heavy use  
  • amphetamines       o 24 to 48 hours  
  • heroin       o 1 to 2 days  
  • morphine       o 1 to 2 days  
  • phencyclidine (PCP)       o 1 to 8 days  
  • alcohol       o 3 to 10 hours  
  • benzodiazepines       o up to 6 weeks with high level use  
  • hydromorphone       o 1 to 2 days  
  • tetrahydrocannabinol (THC)       o 6 to 11 weeks with heavy use  
  • propoxyphene       o 6 to 48 hours  
  • methadone       o 2 to 3 days  
  • codeine       o 1 to 2 days  
  • barbiturates       o up to 6 weeks

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 measured for prescribed or over-the-counter medications (see the specific medication).

Alcohol, prescription medications that are not prescribed, and illegal drugs are not normally present.

What abnormal results mean
The presence of illegal drugs or drugs not prescribed for the person indicates illicit drug use.

Elevated levels of alcohol or prescription drugs can indicate intentional or accidental intoxication and/or overdose.

Additional conditions under which the test may be performed:

  • alcohol withdrawal state  
  • alcoholism  
  • drug abuse monitoring  
  • analgesic nephropathy  
  • at risk for fetal alcohol syndrome  
  • complicated alcohol abstinence (delirium tremens)  
  • delirium  
  • dementia  
  • stroke secondary to cocaine

What the risks are

The risks associated with having blood drawn are:

  • 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

Special considerations
Commonly found substances on a toxicology screen include:

  • alcohol (ethanol) - “drinking” alcohol (see Alcohol and diet)  
  • amphetamines  
  • benzodiazepines  
  • antidepressants  
  • barbiturates and hypnotics  
  • isopropanol - isopropyl alcohol, rubbing alcohol (toxic) (see isopropanol overdose)  
  • methanol - methyl alcohol, found in antifreeze and other substances (toxic)  
  • narcotics  
  • non-narcotic analgesics       o acetaminophen - oral       o 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.

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

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