Volatile substances include the most frequently abused drug - ethanol. Ethanol (ethyl alcohol, drinking alcohol) is the most widely used intoxicant, legal unless it impairs one's performance to operate a motor vehicle or other machinery. Some labratories includes this common drug on all Industrial Drug Screens along with other common volatiles detected simultaneously. These include acetone, occasionally found in diabetics, methanol (grain alcohol), and isopropanol (rubbing alcohol). Ethanol is occasionally found in preplacement screens and frequently found in the large Coma Screens, especially in trauma patients (automobile accidents).
Ethanol in low doses, generally less than 0.04% blood equivalent, is a slight stimulant to humans. It has been demonstrated that a small quantity of alcohol increases the acetylcholine neuroreceptor activity. In larger doses, it has generalized effects graduating from euphoria through stupor. Death generally occurs from unconsciousness and cessation of breathing. This may be complicated by aspiration of vomitus into the lung due to absent gag response. Patients with very high levels may be placed on a respirator or assisted breathing.
Ethanol and Other Drugs
In overdose, ethanol is often found in combination with other drugs - polydrug abuse. Evidence is gathering in scientific literature that the use of marijuana and alcohol together may be more than additive in its effects, i.e. synergistic. This has important consequences for driving under the influence or operation of other machinery. Barbiturates and alcohol are the classic synergistic combination (the interaction of the two drugs so that the sum of the impairment is greater than the individual contributions).
Urine Concentration and Blood Equivalents
Urine concentrations of ethanol, as reported by some labratories, are convertible to blood levels by the following formula: divide the urine concentration by 1.3. For instance, the urine concentration of 0.20% is equivalent to a blood concentration of 0.154%. There is, however, some individual variation in this ratio. Urine levels reflect the average blood concentration over the period of time the urine is produced. To better correlate with current blood levels, a second void may be taken to reflect the blood concentration during the time period between voids.
Ethanol is screened in urine using an automated ethanol dehydrogenase enzymatic assay, and confirmed by quantitative gas chromatography via direct injection with an internal standard on a Carbowax column approved by the FDA for use in clinical laboratories. This gas chromatographic method allows the separation and quantitation by many volatile substances, especially ethanol, but is also useful in quantitation of other abused inhalants such as gasoline or glue (toluene). Positives are repeated with a new sample for confirmations and quantitation. Industrial drug screens are only occasionally positive, but volatiles are frequently found in "for cause" requests. Occasionally, fermentation of urine containing high concentrations of glucose (especially diabetics), is a source of exogenous alcohol. In the event of an alcohol positive in urine, some labratories check for the presence of glucose, and reports it if found.
Cutoff and Detection Post Dose
Using enzyme immunoassay for initial screening and gas chromatography confirmation, volatiles in urine are detected at a cutoff level of 0.04%. Since ethanol metabolizes at 0.02% blood level per hour, detection post dose varies directly with the amount ingested. When an individual no longer feels any effect, ethanol is generally non detectable (less than .02%).