Barbiturates screen, urine

Alternate test name

Lab area

Clinical Biochemistry - General

Method and equipment

Equipment : Roche Cobas pro c503

Method: The assay is based on the kinetic interaction of microparticles in a solution (KIMS)10,11 as measured by changes in light transmission. In the absence of sample drug, free antibody binds to drug‑microparticle conjugates causing the formation of particle aggregates. As the aggregation reaction proceeds in the absence of sample drug, the absorbance increases. When a sample contains the drug in question, this drug competes with the particle‑bound drug derivative for free antibody. Antibody bound to sample the drug is no longer available to promote particle aggregation, and subsequent particle lattice formation is inhibited. The presence of sample drug diminishes the increasing absorbance in proportion to the concentration of drug in the sample. Sample drug content is determined relative to the value obtained for a known cutoff concentration of drug

Expected turn-around time

STAT/Urgent: 3 hours Routine: 24 hours

Specimen type

Urine

Specimen requirements

1.0 mL

Storage and transportation

Special requirements

Background and clinical significance

Barbiturates are a large group of structurally similar sedative-hypnotic drugs which are subject to abuse. Screening assays, such as this, are used to establish the presence or absence of the drug class based on a pre-determined threshold value. Alternative methods must be employed to determine the identity and concentration of any barbiturate from a positive screening result. Barbiturates are grouped in to short-acting and long-acting as follows:

Ultra-short acting: Thiopental
Short acting: Pentobarbital, Secobarbital
Intermediate acting: Amobarbital, Butabarbital, Butalbital
Long acting: Phenobarbital, Barbital

Sedative-hypnotics are a large group of drugs which cause CNS depression. Most stimulate the activity of Gamma Aminobutyrate (GABA), the principle inhibitory neurotransmitter in the CNS. Similar to the barbiturates, the sedatives can be grouped into short-acting and long-acting as follows:

Short acting: Methyprylon
Intermediate acting: Glutethimide, Meprobamate, Methaqualone

Many of the symptoms seen with barbiturate toxicity are also observed with the sedative-hypnotics. These include lethargy, coma, hypothermia, slurred speech, irritability, respiratory depression and cardiovascular complications.