Significance of an Anion Gap and an Osmol Gap in Poisoning

Moon, Sung Woo; Kim, Soo jin; Hong, Suk Hyeon; Jun, Jung Min; Lee, Sung Woo; Hong, Yun Sik

Abstract

PURPOSE
In the management of acute poisoning, the anion gap and the osmol gap are easily derived from serum laboratory findings and arterial blood gas analysis. The anion gap is known to be increased by the effects of the toxic material itself and secondary complications or by an exacerbation of an underlying illness. The osmol gap can be increased by the presence of osmotically active materials in the body, such as alcohol, glycols and mannitol. This study was proposed to investigate the significance of an increased anion gap in acutely poisoned patients and the effect of alcohol ingestion in increasing the osmol gap, which might help to understand the significance of an increased osmol gap in acutely poisoned patients.
METHODS
A retrospective chart review of poisoned patients who had visited the emergency departments of the Anam and the Ansan hospitals of Korea University was used in this study. Serum laboratory findings and arterial blood gas analysis were used to measure the anion gap and the osmol gap. Patients were categorized into a non anion-gap group versus a high anion-gap group and a normal osmolgap group versus a high osmol-gap group. Frequency of toxidrome, blood pH and drinking history were included to evaluate the relations between the groups.
RESULTS
Of 204 patients, 195 patients who completed the tests were included in the study. In the 99 patients with a high anion-gap, 38 (38.38%) patients showed development of toxidrome. In the 96 patients with a non anion-gap, only 15 (15.62%) patients showed toxidrome. Forty-six (80.7%) of the 57 patients with a high osmol-gap and 20 (22.2%) of the 90 patients with a normal osmol-gap had a history of drinking.
CONCLUSION
In poisoned patients, the group with a higher anion gap showed a higher frequency of toxidrome. This suggests that in the management of a poisoning victim with an uncertain history, should a high anion gap be found, an intense observation and evaluation is necessary to identify the cause. An increase in the osmol gap in poisoned patients is generally considered to be from alcohol ingestion. Thus, for a patient with an increased osmol gap, measurement of the serum ethanol level should be done to exclude the effect of alcohol.