4.19: Alcohol

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Three samples are sent to the laboratory for alcohol analysis. The patients are reported to be in varying states of coma; severe coma, mild coma, and sleepy drunk.

An alcohol screen by enzyme assay for each patient is reported as 3700 \(\mu\)g/mL, 2400 \(\mu\)g/mL, and negative, respectively. However, the patient with the negative result has a reliable history of drinking in the 24 hours before admission to the emergency room. The stat lab is requested to perform a repeat alcohol analysis on the serum sample. The same result is obtained.

QUESTIONS

Is it possible to predict the blood alcohol levels of each patient from their clinical appearance?
The lab is requested to repeat the analysis a third time. In addition, all the samples are cross-checked using a semiquantitative diffusion method. The diffusion test gives an extremely positive result for all three samples. What could explain the difference between the quantitative and qualitative results?

Questions to Consider

Are the acute effects of alcohol dose related?
Do these effects vary from individual to individual? Is it possible to predict the effect of a specific blood alcohol level on a single individual? Why?
What blood levels of ethanol are often associated with coma? Will the serum alcohol values help in treatment?
What other agents could exacerbate the clinical effects of alcohol, causing, for example, a deeper coma than might otherwise be expected?
What are the procedures available to screen for alcohol? To quantitate ethanol?
How specific for the presence of ethanol are the assays employed by this laboratory?
What other method would be useful in resolving the discrepancies between the results?

Answer

It is very difficult to predict, within a narrow range, the concentration of a blood alcohol level from the clinical appearance of the patient. The blood levels can vary greatly from individual to individual with the same symptoms.
The difference between the results obtained for the third patient by the qualitative and quantitative tests can be explained by the presence of some volatile alcohol other than ethanol. This alcohol would not be detected by the specific enzymatic assay but would be detected by the non-specific diffusion assay or by gas chromatographic analysis.

Answers to Questions to Consider

The effects of a toxicant such as alcohol are generally dose related, as shown on p 642 in Chapter 34 and in the chapter on Alcohol on the CD-ROM. In a general population, the greater the dosage, the greater the severity of the clinical response, i.e. coma, etc.
There is a great variation in individual response to the presence of ethanol. Ethanol is metabolized by a series of inducible liver enzymes, especially alcohol dehydrogenase. Individuals who are chronic abusers of alcohol have higher levels of activity of these enzymes and thus can metabolize ethanol more rapidly than the occasional drinker. In addition, a chronic ethanol abuser develops a physiological tolerance to this drug and thus will have fewer clinical symptoms. Thus, it is difficult to predict the effect of the same dose on different individuals (p 641).
Values above 3000 \(\mu\)g/mL are generally associated with coma (see p 642). Serum alcohol values will help in treatment only if they are very high--usually 4000 to 6000 \(\mu\)g/mL. At these levels, aggressive intervention such as dialysis may be used.
A very deep grade IV coma associated with ingestion of alcohol would tend to make the physician think of drugs and other non-therapeutic agents as well as other pathologic causes, e.g. hypoglycemia. Usually a drug screen would be ordered in this circumstance.
Procedures available for screening for alcohol in most laboratories include enzymatic and diffusion assays (See Method forAlcohol on CD-ROM). The enzymatic assays are based on the enzyme alcohol dehydrogenase. The rarely employed diffusion assays measure any volatile, reducing substance.
The enzyme method is fairly specific for ethanol and would not record the presence of substances such as methanol, isopropanol and ethylene glycol. In contrast, the diffusion method is sensitive to the presence of any volatile alcohol and would be positive for methanol and isopropanol. In this case, a more specific method should be used to determine the toxic agent.
Gas chromatography would probably show that some other alcohol, such as methanol, was present.