Accuracy of body mass index in volunteer firefighters.

BACKGROUND

Obesity is prevalent among career firefighters and may contribute to heart attacks, a leading cause of on-duty fatalities. The US National Fire Protection Association estimates that 800 000 of 1.1 million firefighters are volunteers. Body mass index (BMI) is commonly used to assess obesity, but little is known about its accuracy in volunteer firefighters, in whom muscle mass may be higher, given firefighting's physical demands, reducing its accuracy in identifying obesity.

AIMS

To evaluate the accuracy of BMI in identifying obese volunteer firefighters.

METHODS

Height, weight and body composition were measured in 73 male volunteer firefighters (mean age 40±12). The proportions with BMI ≥ 25kg/m(2), ≥30kg/ m(2) and percent fat ≤ 20th percentile were determined. Using the age-specific 20th percentile for percent fat (Cooper Clinic) as the criterion for being over-fat, the accuracy of BMI was assessed using sensitivity and specificity calculations.

RESULTS

The means ± standard deviation of BMI and percent fat were 32±6 and 25±5, respectively. The proportions with a BMI ≥ 25 and ≥30 were 90% and 60%, respectively. Fifty-one percent had a percent fat ≤ 20th percentile. The measure BMI ≥ 25 had a perfect sensitivity (1.0) and low specificity (0.19) and BMI ≥ 30 had a high sensitivity (0.89) and moderate specificity (0.69).

CONCLUSIONS

Although BMI ≥ 30 accurately predicted being over-fat, it misclassified large and lean firefighters. Although BMI should be used cautiously, it can identify over-fat firefighters at risk of cardiovascular disease, and its measurement is cost-effective and simple.