Laboratory Studies
Following consumption of any type of alcohol, the extent of the workup depends partly on the history. However, because the patient's sensorium is likely to be altered and a history unobtainable or inaccurate, a thorough physical examination is important to evaluate for occult injuries and laboratory clues can also become invaluable.
If the the possibility of a suicide attempt is raised, an electrocardiogram and basic toxicology screen, including measurement of salicylate and acetaminophen concentrations, become important.
In addition, if ingestion of a toxic alcohol is suspected, a serum ethanol level and basic electrolytes, including a serum bicarbonate level are vital, as the latter are needed to calculate an anion gap. In such a situation, specific serum toxic alcohol levels immensely help guide management. If these are unavailable, calculation of an osmolar gap can sometimes be helpful, though its exclusive use is fraught with pitfalls.[11] These issues are best discussed with the local poison control center. Arterial blood gases and other tests that measure associated organ dysfunction also become important in cases of poisoning with toxic alcohols.
An important point is that laboratory abnormalities vary dramatically over the course of the patient's presentation and any laboratory abnormalities must be interpreted with the time frame of the patient's presentation in mind. Failing to do so is a common and important pitfall. Thus, early in the course of intoxication with a toxic alcohol, a patient will have neither an anion gap nor an osmolar gap though their serum toxic alcohol level will be highest shortly after ingestion. However, as metabolism of the toxic alcohol occurs, the anion and osmolar gaps develop as metabolites are formed and the toxic alcohol level drops.[12] Other laboratory abnormalities also develop as end-organ damage occurs. Coingestion of alcohol delays all the laboratory value changes as well as the signs and symptoms of toxic alcohol-induced injury.
- Ethanol
- The single most important laboratory test in a patient who appears intoxicated with ethanol is a serum glucose level. Hypoxia, head injury, seizures, and other metabolic disturbances must be excluded by either history or physical examination or sought with the appropriate tests. The routine use of a serum blood alcohol level is controversial, largely because it is unlikely to affect management in a patient who is awake and alert. Many clinicians consider the patient safe for discharge once they are clinically (not numerically) no longer intoxicated.
- In patients who are chronic alcoholics, anemia, thrombocytopenia, elevation of hepatic transaminase levels, and a prolongation of the prothrombin time can be observed. These need not be routinely checked in a patient who presents simply for alcohol intoxication but may be useful if changes from baseline are suspected.
- Isopropanol
- Serum levels of isopropanol can be obtained but are somewhat of limited value, as the treatment is largely supportive. However, they can be useful in confirming the diagnosis. After correcting for all other variables, including ethanol, the serum isopropanol level can be estimated by multiplying the remaining osmolar gap by 6.0. Serum ketones will often be positive, although the patient should not be acidotic. Because ketones will be present in the serum as recently as 30 minutes after ingestion, if there is no coexisting ethanol ingestion, the absence of ketones effectively rules out isopropanol ingestion.
- Depending on the assay used in the laboratory, significant ketosis can cause interference with the creatinine assay. As such, the serum creatinine level can be falsely elevated.
- Methanol
- Serum methanol levels should be obtained when this diagnosis is suspected. As previously stated, both the osmolar and anion gap should be obtained.
- After correcting for all other variables, including ethanol, the serum methanol level can be estimated by multiplying the remaining osmolar gap by 3.2.
- Ethylene glycol
- A serum ethylene glycol level should be obtained when this diagnosis is suspected. The osmolar gap and anion gap should also be obtained. After correcting for other variables, including ethanol, the serum ethylene glycol level can be estimated by multiplying the remaining osmolar gap by 6.2.
- A baseline creatinine and BUN level should be obtained in all cases of ethylene glycol intoxication. These values can then be followed to check for the development of renal failure.
- In addition, the urine can be examined for evidence of fluorescence. In antifreeze, fluorescein is added to the liquid to permit mechanics to identify the source of a fluid leaking from a car. However, fluorescein is excreted in the urine faster than ethylene glycol. Thus, fluorescence can be eliminated before the patient even arrives in the emergency department. As such, the presence of fluorescence of urine under a Wood's lamp is not a sensitive test. In addition, because certain containers themselves fluoresce, the presence of fluorescence is neither sensitive nor specific. Despite this, a positive test that differentiates urine fluorescence from that of its container may be a quick bedside clue pointing toward ethylene glycol intoxication. Both a serum calcium level and an electrocardiogram should be obtained, since hypocalcemia may occur as calcium combines with oxalate in the form of calcium oxalate crystals.
Procedures
Measuring the osmolar gap is important when toxic alcohols ingestion is suspected. The osmolar gap is determined by subtracting the calculated osmolality from the measured osmolality. The serum osmolality should be determined by freezing point depression rather than by heat of vaporization.
The serum osmolality can be calculated by the following formula:
Osm = (2) (Na+) + BUN/2.8 + Glucose/18 + EtOH/4.6 + Isopropanol/6.0 + MeOH/3.2 + Ethylene glycol/6.2
In the above formula, if, for example, an ingestion of methanol is suspected, the osmolality should be calculated using the sodium, BUN, and glucose. The ethanol level is also measured and then factored into the equation. If isopropanol and ethylene glycol are not suspected, they can be eliminated from the equation. Then, once the osmolar gap is determined, multiply the osmolar gap by 3.2 to determine the estimated methanol level.
It is important to recognize that neither the presence nor absence of an osmolar gap can be used to confirm or exclude a toxic alcohol ingestion. With both methanol and ethylene glycol, the alcohols are metabolized from an alcohol to an aldehyde, and ultimately to an acid. As such, shortly after an ingestion, the patient may have an osmolar gap without an anion gap. Similarly, in the later stages of an ingestion, a patient may have an anion gap without an osmolar gap.
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