[Usefulness of blood formic acid detection in the methanol poisoning in the practice of clinical toxicology department-preliminary assessment].

BACKGROUND: Severe metabolic acidosis is one of the most difficult diagnostic and therapeutic challenges. The most common causes of this type of acid-base balance disorder are toxic alcohols, e.g. methanol poisoning. Metabolites of methanol, formaldehyde and formic acid are responsible for severe symptoms of this poisoning.

OBJECTIVE: The aim of this study is a preliminary assessment of usefulness of formic acid detection by gas chromatography in the daily practice of clinical toxicology department in methanol poisoning confirmed by the designation of this alcohol in the blood.

METHODS: The study included 9 patients from Greater Poland region diagnosed with methanol poisoning. Blood samples were collected during routine laboratory tests, on admission secured at-80°C, and then formic acid was determined by head-space gas chromatography. The relationship between the concentration of blood formic acid and methanol, ethanol, and the acid-base balance parameters were evaluated.

RESULTS: The study group consisted of 9 men, aged 49.89 ± 6.17 years. All patients were diagnosed with alcohol dependence. In most cases (66.67%) and methanol poisoning occurred during ethanol abuse. The average blood methanol and ethanol concentrations were 2.48±1.74 g/L and 0.99±1.73 g/L respectively. The average blood formic acid concentration was 0.59±0.46 g/L, from 0.0 to 1.12 g/L. Acid-base balance parameters were (mean± SD): pH 7.00 ±0.36; pCO2 32.26 ± 14.54 mmHg; PO2 114.24±77.53 mmHg; BE -18.28 16.76 mmol/L; HCO3-12.70±11.53 mmol/L. There was a positive correlation be- tween the blood methanol and formic acid concentration. A negative correlation was found between the blood ethanol and formic acid concentration. In patients with positive blood ethanol concentration (1.74 to 5.0 g/L, mean 2.96±1.78 g/L) there was not any formic acid, despite the presence of methanol was confirmed. These patients did not demonstrate metabolic acidosis (mean±SD): pH 7.43 ±0.20; HCO3- 27.87 ± 2.36 mmol/L; BE 3.60 ±2.40 mmol/L. In contrast, in all patients with negative blood ethanol concentration, tests confirmed metabolic acidosis and elevated formic acid (mean SD): pH 6.80±0.20; HCO3- 5.12±1.67 mmol/L; BE-29.20±3.68 mmol/L; formic acid 0.89±0.16 g/L.

CONCLUSION: Methanol poisoning cannot be confirmed by positive blood formic acid in patients with high blood ethanol concentration (≥1.74 g/L). In this kind of intoxication severe metabolic acidosis does not occur too. In patients with no detectable blood ethanol concentration, blood formic acid concentration can reach 1.12 g/L and correlates with the severity of metabolic acidosis.