A case of a drug intoxication patient who showed a discrepancy in blood Na levels between the direct electrode method and the dilution method

Abstract

Blood gas analyzers can simultaneously measure not only gas analysis but also many other test items such as electrolytes, glucose, creatinine, and hemoglobin. Therefore, essential tests can be quickly obtained for initial medical treatment at the emergency scene or to assess the patient’s general condition in the event of a sudden change in medical condition. In the present case, we experienced a discrepancy between sodium (Na) levels measured by a blood gas analyzer (direct electrode method) and a general-purpose automatic analyzer (ion selective electrode dilution method) in a patient transported to our Advanced Emergency Medical Center for suspected drug poisoning. The results of the time series analysis of electrolyte parameters and blood drug detection after the patient’s arrival and the results of the addition test also suggested that the phenomenon of high Na deviation in the direct method was caused by atomoxetine. We searched for similar cases of sodium level deviation in past drug intoxication cases analyzed in our toxicology laboratory, and found no cases of high sodium level deviation, including drugs similar to the present case. The accompanying documentation for the blood gas analyzer listed several substances as interfering with sodium measurement, but did not list Atomoxetine, which was obtained in the present case. It is important to recognize that blood gas analyzers, which play an important role in initial medical care, are subject to a variety of interferences from a wide range of measurement items, and any discrepancies in measurements should be accurately reported to the clinical side.