Widmark’s Formula
Forensic Toxicology: Blood Alcohol Concentration (BAC) Estimation
1. The Equation
Widmark’s formula is used to estimate the theoretical peak Blood Alcohol Concentration (BAC) following the ingestion of a known quantity of alcohol:
$$BAC = \frac{A}{W \times r}$$
- A: Mass of ethanol consumed (in grams).
- W: Body weight of the individual (in kilograms).
- r: Widmark factor (distribution constant).
2. Widmark Constants (r)
| Population | Average ‘r’ Value |
|---|---|
| Adult Men | 0.68 – 0.70 |
| Adult Women | 0.55 – 0.60 |
3. Forensic High-Yield Pearls
- Elimination Rate: Widmark also proposed an elimination rate ($\beta$), which averages approximately 15 mg/dL per hour, though this varies significantly among individuals.
- Limitations: The formula provides a theoretical peak and does not account for individual metabolic differences, gastric emptying time, or food intake, which can delay absorption.
- Medico-Legal Use: Essential in forensic reconstruction of alcohol-related cases (e.g., DUI/DWI accidents) where back-calculation is required to estimate BAC at the time of an incident.
- Educational Resource: For further study on forensic toxicological calculations and practice questions, visit mymedschool.org.