Rethinking the Limit of Detection for Serum Ethanol: Evidence from a Clinical Laboratory

Ethanol is a widely consumed psychoactive substance. Serum concentrations above 100 mg/dL can cause cognitive impairment and confusion, while levels exceeding 300 mg/dL may be fatal. Thus, rapid and accurate determination of blood ethanol concentration is crucial for diagnosing and managing acute intoxication. Ethanol measurement also has important legal implications, such as in traffic accidents or criminal proceedings. Gas Chromatography-Mass Spectrometry (GC-MS) is the reference method for ethanol determination due to its accuracy and specificity. In routine clinical laboratories, however, ethanol quantification is usually performed using enzymatic spectrophotometric assays. Alcohol dehydrogenase (ADH) oxidizes ethanol to acetaldehyde with NAD as coenzyme, which is simultaneously reduced to NADH. The increase in NADH absorbance at 340 nm allows indirect quantification of ethanol. Although analytical characterization and method optimization are the manufacturers' responsibilities, literature indicates these processes are not standardized, and specific procedures are generally not disclosed. Consequently, clinical laboratories may need to verify these values, particularly during implementation of new methods, internal validation, or when analytical results conflict with clinical presentation. We report four cases in our laboratory with positive ethanol results of 11-14 mg/dL that, after reprocessing, were reported as "not detected". This highlights the need to determine the smallest analyte quantity detectable with certainty, commonly expressed as the limit of detection (LoD).