Toxicity, Ethylene Glycol Workup

Patients who ingest ethylene glycol may initially have few, if any, metabolic disturbances. Serum concentrations of ethylene glycol may be measured; however, at some health care facilities, these results are not available for 2 or more days. Thus, ethylene glycol levels are often not determined early enough to be useful in emergency treatment. For institutions that frequently treat ethylene glycol toxicity cases, in-hospital rapid laboratory confirmation may become cost-effective because of the institutional cost-benefit ratio evaluation that compares antidotal therapy, ethanol therapy, and hemodialysis therapy. Emergency departments located in larger metropolitan areas may negotiate availability of this test at regional clinical laboratories.

A study by Long et al suggests that a rapid qualitative colorimetric test (ethylene glycol test [EGT] kit), already in use by veterinarians, may be used by medical facilities as well. Using ethylene glycol added to human samples, the reported sensitivity was 100% (95% confidence interval [CI], 70-100%), and specificity was 88.8% (95% CI, 52-100%).^[3] Although the use of such a test is promising, it has not been validated in human exposures and is thus not widely available to clinicians.

• Serum osmolality: Because ethylene glycol levels are not reported in a clinically helpful fashion in most institutions, ethylene glycol exposure level is often estimated through measurement of the serum osmolality. This estimate is obtained by sampling a set of electrolyte levels (eg, BUN, creatinine, glucose) and calculating the expected osmolality in the patient's serum. A serum osmolality is then measured, and the difference between the measured and calculated osmolality (the osmolal gap) is determined. Several formulas are effective for calculating the osmolality from serum electrolytes and other solutes.

  • The most commonly used formula is 2(Na⁺ level) + BUN level/3 + glucose level/18 = calculated osmolality. The sodium level is measured in mEq, and the BUN and glucose levels are measured in mg/dL.
  • The osmolal gap is determined by subtracting the calculated osmolality from the measured osmolality (osmol [measured] - osmol [calculated] = osmolal gap). The serum osmolality must be determined by freezing-point depression rather than by boiling point elevation. This is because, with the boiling technique, the toxic alcohols are vaporized rapidly, and, thus, a falsely low or normal estimate of the osmolality is obtained. Once the osmolal gap is determined, estimating the serum levels of ethylene glycol or another alcohol is possible by applying the following conversion factors: ethylene glycol = 6.2, methanol = 3.2, and ethanol = 4.6.
  • If the ethanol level is measured simultaneously with the electrolyte levels, its contribution can be subtracted to determine an approximate contribution of the toxic alcohol. If the clinician does not wish to memorize the conversion factors, they can be calculated by dividing the molecular weight by 10. For example, the conversion factor for ethanol would be calculated by adding the molecular weight of 2 carbons = 2 X 12, 1 oxygen = 16, and 6 hydrogens = 6. Thus, 24 + 16 + 6 = 46. This divided by 10 reveals the conversion factor for ethanol, which is 4.6. Most clinicians prefer to look these values up in a table.
  • Serum electrolyte levels are also useful later in the course of intoxication because they can reveal the presence of anion gap acidosis. This information may be important when determining the need for dialysis and other interventions. The goal of therapy, however, is to treat the patient before acidosis develops.
• Additional laboratory tests that should be obtained in symptomatic patients include the following:

  • Serum calcium level determination is recommended.
  • Arterial blood gas determination is recommended.
  • Urinalysis: Urine may reveal the presence of calcium oxalate crystals, a sign usually observed late in the process of intoxication. Oxalate crystals typically have the shape of a folded envelope.
  • Another technique, popularized by the television series "ER," is to shine a Wood lamp (UV light) on an early sample of urine. If a sufficient fluorescein level is present in the radiator fluid, the urine fluoresces.^[4] The urine should be compared to a control sample. If the radiator fluid contains fluorescein, a green-colored glow may be observed in a dark room. This light also may be used to detect possible ethylene glycol on clothing or the patient.

Imaging rarely contributes to the specific diagnosis of ethylene glycol intoxication, but it may be useful as needed for routine care of these patients.

Other tests that may be useful depending on the clinical status of the patient include electrocardiography (ECG) and CT scan of the brain. Use of a Wood's (ultraviolet) lamp has been discussed above. A microscope may be useful for identifying calcium oxalate crystals, as noted above.