Practical cut off values to determine body mass index

We tried to understand whether there are significant cut off values simply determining body mass index (BMI). The study was performed in Internal Medicine Polyclinics on consecutive check up patients aged between 15 and 70 years to see possible consequences of excess weight on health and to avoid debility induced weight loss in elders. Insulin using diabetics and patients with devastating illnesses were excluded to avoid their possible effects on weight. Cases were subdivided into three groups according to their body weights as under 65, between 65 and 85, and above 85 kg groups and prevalences of underweight, normal weight, overweight, and obesity were determined. Sensitivity, specificity, and positive and negative predictive values of body weights to determine BMI were calculated. The study included 954 cases (566 females). Sensitivity of 65 kg as a cut off value to detect normal weight was 61.0%, specificity 94.3%, positive predictive value 82.9%, and negative predictive value was 97.6%. Similarly, sensitivity, specificity, and positive and negative predictive values of 65 and 85 kg to detect overweight cases were 71.5%, 63.3%, 56.2%, and 77.1% respectively. So both values were statistically significant to detect normal weight, overweight and obese individuals (p = 0.000 for both). Although BMI is probably a more valuable parameter to show weight status, the cut off values of 65 and 85 kg, as an easier way, have significant places, too.