In forensic alcohol analysis, the Widmark formula is used to estimate blood alcohol concentration (BAC) from the amount consumed. The formula is C = A / (r × W), where C is BAC (g/dL), A is alcohol consumed (grams), W is body weight (kg), and r is the Widmark distribution factor. The correct r values for males and females respectively are:

• A 0.6 for males; 0.5 for females
• B 0.7 for males; 0.6 for females ✓
• C 0.8 for males; 0.7 for females
• D 0.5 for males; 0.4 for females

Explanation

The Widmark r factor (volume of distribution coefficient) reflects the fact that ethanol distributes in total body water. Males have proportionally more lean muscle mass (higher water content), giving r ≈ 0.7 (range 0.6–0.8). Females have proportionally more body fat (lower water content per kg), giving r ≈ 0.6 (range 0.5–0.7). This means a given dose of alcohol produces a higher BAC in women. Forensic laboratories use r = 0.68 for males and 0.55 for females as population averages. The Widmark equation is used retrospectively to calculate how much alcohol was consumed or to back-calculate BAC at a specific time.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.