From the FDA Drug Label
The diagnosis of these poisonings may be difficult because ethylene glycol and methanol concentrations diminish in the blood as they are metabolized to their respective metabolites Hence, both ethylene glycol and methanol concentrations and acid base balance, as determined by serum electrolyte (anion gap) and/or arterial blood gas analysis, should be frequently monitored and used to guide treatment Treatment success should be assessed by frequent measurements of blood gases, pH, electrolytes, BUN, creatinine, and urinalysis, in addition to other laboratory tests as indicated by individual patient conditions At frequent intervals throughout the treatment, patients poisoned with ethylene glycol should be monitored for ethylene glycol concentrations in serum and urine, and the presence of urinary oxalate crystals. Similarly, serum methanol concentrations should be monitored in patients poisoned with methanol
The laboratory signs of methanol poisoning include:
- Elevated anion gap due to metabolic acidosis
- Increased osmolar gap
- Visual disturbances
- Oxalate crystals in the urine
- Elevated serum methanol concentrations
- Abnormal blood gas analysis
- Electrolyte imbalances
- Azotemia 1
From the Research
Laboratory signs of methanol poisoning include a high anion gap metabolic acidosis, elevated osmolal gap, low bicarbonate levels, and increased serum methanol concentration, as evidenced by studies such as 2, which highlights the importance of early recognition and treatment. The diagnosis of methanol poisoning is often made in the presence of high index of suspicion of toxic alcohol ingestion, early visual symptoms, unexplained anion gap metabolic acidosis, and significant osmolar gap, as noted in 3. Key laboratory findings include:
- High anion gap metabolic acidosis, with an anion gap often greater than 20 mEq/L
- Elevated osmolal gap, exceeding 10 mOsm/kg due to the presence of methanol and its metabolites
- Low bicarbonate levels, often below 20 mEq/L
- Increased serum methanol concentration, with levels above 20 mg/dL considered toxic and severe poisoning typically showing levels above 50 mg/dL
- Elevated lactate levels and formic acid levels, which correlate with visual disturbances
- Mild elevations in liver function tests These laboratory abnormalities develop within 12-24 hours after methanol ingestion as the parent compound is metabolized to its toxic metabolites, making early recognition crucial for timely intervention with fomepizole or ethanol therapy to block this metabolism, as discussed in 4 and 2. It is essential to note that the presence of both laboratory abnormalities concurrently is an important diagnostic clue, although either can be absent, depending on the time after exposure when blood is sampled, as mentioned in 2. Given the potentially high morbidity and mortality of methanol poisoning, it is crucial for clinicians to have a high degree of suspicion for this disorder in cases of high anion gap metabolic acidosis, acute renal failure, or unexplained neurologic disease, as emphasized in 2, to initiate treatment early and improve patient outcomes.