Early diagnosis is essential for successful treatment in
methanol poisoning.
Methanol detection by gas chromatography is not available in most hospitals.
Methanol increases the osmolal gap in serum and its metabolite
formate increases the anion gap. The sensitivity of these indirect diagnostic methods is not good at low concentrations of
methanol or
formate. We therefore studied the usefulness of
formate measurement in diagnosing
methanol poisoning. In 15 patients poisoned with
methanol, serum
formate was measured enzymatically on a Cobas Mira analyzer using
formate dehydrogenase and nicotinamid
adenine dinucleotid. Day-to-day coefficient of variation was 5%, and the upper reference limit was 2 mg/dL (0.4 mmol/L).
Methanol was detected in all 15 patients of whom 14 had elevated serum
formate concentrations. Anion gap was increased in 11 of 11, and osmolal gap in 11 patients of 15 examined.
Metabolic acidosis was present in 12 of 15 patients, but pH was below 7.30 in only 9 of them. Four patients with no symptoms had
formate concentrations in the range 2-38 mg/dL (0.5-8.3 mmol/L), indicating that increased serum
formate was a sensitive
indicator of
methanol poisoning. Our results proved
formate analyzes to be a simple, sensitive, and specific way of diagnosing
methanol poisoning. Confounders are patients admitted early, or concomitant
ethanol ingestion, and therefore no
acidosis. This problem may, however, be omitted by repeated
formate analysis in patients developing
metabolic acidosis.