Normal Blood Alcohol Level in Healthy Adults
In healthy adults who have not consumed alcohol, the normal blood alcohol concentration (BAC) is 0.00 g/dL (zero). 1
Clinical Context
Zero BAC is the physiological baseline for individuals who have not consumed alcohol, representing the absence of ethanol in the bloodstream 1
Any detectable blood alcohol level above 0.00 g/dL indicates recent alcohol consumption, though the clinical significance varies based on the concentration 2
Important Thresholds for Clinical Reference
While zero is the normal baseline, understanding clinically relevant BAC thresholds helps contextualize abnormal values:
Legal and Impairment Thresholds
0.08 g/dL (80 mg/dL) is the legal intoxication threshold in the United States for driving and represents the NIAAA definition of binge drinking 1
Cognitive impairment begins at much lower levels: BAC of approximately 0.03% (30 mg/dL) already causes significant impairment in visual information processing, response times to optical stimuli, and decision-making for complex tasks 3
0.05 g/dL (50 mg/dL) represents a level where virtually all drivers show measurable impairment, with relative risk of fatal single-vehicle crash being 7-21 times higher than at 0.00 BAC 4
Clinical Assessment Ranges
20-200 ng/mL phosphatidylethanol (PEth) correlates with moderate alcohol consumption of 20-60 g/day (approximately 1.5-4 standard drinks daily), which may be relevant when assessing metabolic dysfunction and alcohol-related liver disease 2
PEth >200 ng/mL (typically >500 ng/mL) indicates heavy drinking exceeding 50-60 g/day and suggests alcohol-related liver disease risk 2
Mean BAC of 143-182 mg/dL has been used in trauma research to define clinically significant intoxication 1
Common Clinical Pitfalls
Do not assume "social drinking" means normal BAC: Even 1-2 drinks can produce measurable BAC and cognitive impairment for several hours 3
Individual tolerance varies significantly: Chronic heavy drinkers may have fatal BAC levels averaging 355 mg/dL, significantly higher than acute intoxication in non-tolerant individuals 5
The 0.11% BAC threshold for hangover is outdated: Subjective intoxication, not absolute BAC, better predicts hangover severity, and many individuals experience hangovers at lower BAC levels 6
Patients with very high BAC (≥400 mg/dL) may present with less severe trauma than expected but represent a high-risk population with evidence of chronic alcohol use disorder requiring intervention 7