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Interpretive Handbook

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Test 505335:
Drug of Abuse, Barbiturate Screen with GC-MS Confirmation, Urine

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Barbiturates constitute a class of central nervous system depressants. They are classified on their duration of action. The duration of action is approximately 15 minutes for the short-acting types (eg, secobarbital and pentobarbital), and a day or more for the long-acting types (eg, phenobarbital). Short-acting barbiturates are usually excreted in the urine as metabolites, while the long-acting barbiturates appear primarily unchanged.

 

Barbiturates were originally introduced as sleep inducers. Butalbital also is used to control severe headaches. Mephobarbital and phenobarbital are frequently used to control major motor (grand mal) seizures.

 

These drugs are commonly abused as "downers" to induce sleep after an amphetamine- or cocaine-induced "high".

Useful For Suggests clinical disorders or settings where the test may be helpful

Screening and confirming drug abuse involving barbiturates such as amobarbital, butalbital, pentobarbital, phenobarbital, and secobarbital.

Interpretation Provides information to assist in interpretation of the test results

The presence of barbiturate in urine at >300 ng/mL indicates use of one of these drugs. Most barbiturates are fast acting; their presence indicates use within the past 3 days. Phenobarbital, commonly used to control epilepsy, has a very long half-life. The presence of phenobarbital in urine indicates that the patient has used the drug sometime within the past 30 days.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements. This test is very specific for these compounds.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

Positives are reported with a quantitative GC-MS result.

EMIT cutoff concentration: 200 ng/mL

Clinical References Provides recommendations for further in-depth reading of a clinical nature

Baselt RC, Cravey RH: Disposition of Toxic Drugs and Chemicals In Man. 3rd edition. Chicago, IL Year Book Medical Publishers, 1989