False Elevations of Blood Alcohol Levels
The most clinically significant causes of falsely elevated blood alcohol levels are specimen contamination from alcohol-containing skin disinfectants during collection, delayed sample processing allowing microbial fermentation, and interference from certain medications and substances containing ethanol or isopropanol.
Pre-Analytical Factors
Specimen Collection Issues
- Alcohol-based skin disinfectants (e.g., isopropyl alcohol, ethanol swabs) used during venipuncture can contaminate blood samples and falsely elevate measured alcohol levels 1, 2
- Use non-alcohol-based antiseptics (such as povidone-iodine or chlorhexidine) when collecting blood for alcohol testing to avoid this common pitfall 1
Sample Handling and Storage
- Microbial fermentation can occur in blood samples if not properly preserved or if processing is delayed, leading to in vitro production of ethanol from glucose 3
- This is particularly problematic in samples with elevated glucose levels or those stored at room temperature for extended periods 3
- Samples should be collected in tubes containing sodium fluoride (which inhibits glycolysis and microbial growth) to prevent false elevations 3
Medication and Substance Interference
Alcohol-Containing Pharmaceuticals
- Over 500 proprietary pharmaceutical products contain ethanol in concentrations ranging up to 68%, which can contribute to measurable blood alcohol levels 1, 2
- Common categories include oral liquid medications (cough syrups, elixirs), mouthwashes, and certain parenteral preparations 1, 2
- Patients consuming multiple alcohol-containing medications throughout the day may accumulate significant ethanol exposure, with some oral preparations containing 40% or more alcohol 1
Isopropanol Interference
- Isopropanol (found in rubbing alcohol and some topical preparations) is metabolized to acetone, and certain laboratory methods may cross-react or misidentify this as ethanol 1
- This can occur with both ingestion and dermal absorption of isopropanol-containing products 1
Laboratory Method Considerations
Analytical Interference
- Certain colorimetric methods used for alcohol testing can produce false-positive or false-negative results depending on interfering substances 3
- The specific analytical method used (enzymatic, gas chromatography, etc.) affects susceptibility to interference 3
Clinical Context Factors
Dilute Specimens
- Very dilute urine samples (creatinine <2 mmol/L) can produce misleadingly elevated results when normalized to creatinine concentration, though this applies more to urinary metabolite testing than direct alcohol measurement 3
Important Clinical Caveats
- When blood alcohol levels seem inconsistent with clinical presentation, always consider pre-analytical errors first before attributing discrepancies to patient factors 1, 2
- Document the type of skin preparation used during blood collection in cases where alcohol levels will be used for legal or critical clinical decisions 1
- Medication reconciliation should include review of all liquid medications, over-the-counter products, and mouthwashes in patients where alcohol exposure is being assessed 1, 2
- Request repeat testing with proper collection technique if contamination is suspected rather than relying on potentially erroneous initial results 1