Body Mass Index in Amputees

Whereas estimates of percent deviation of body weight from ideal (FΔweight) are corrected for amputation, those of body mass index (BMI) are not, creating discrepancies in evaluating obesity. A correction of the BMI formula for amputation is proposed. The formula for BMI was corrected for amputation mathematically. The mathematical model predicts that the uncorrected BMI formula underestimates body fat in unilateral amputees and overestimates body fat in subjects with bilateral amputations at the same length of the legs. FΔweight and corrected and uncorrected BMI estimates were computed in 15 subjects with unilateral leg amputation and in 8 subjects with multiple amputations. BMI estimates were as follows: in unilateral amputees, corrected 24.1 ± 4.1 kg/m 2 , uncorrected 22.2 ± 3.9 kg/m 2 (p <.001); and in multiple amputees, corrected 21.6 ± 2.4 kg/m 2 , uncorrected 32.6 ± 11.8 kg/m 2 (p =.043). Linear regressions of FΔweight obtained from standard nutrition assessment on FΔweight computed from uncorrected and corrected BMI values were as follows: in unilateral amputees, uncorrected FΔweight = ‐0.079 + 0.932 X actual FΔweight, r =.974, p <.01, and corrected FΔweight = 0.002 + 1.005 X actual FΔweight, r =.997, p <.01; in multiple amputees, uncorrected FΔweight = 0.528 + 1.930 X actual FΔweight, r =.607, p is not significant, and corrected FΔweight = ‐0.010 + 0.920 X actual FΔweight, r =.936, p <.01. Uncorrected BMI estimates erroneously classified two obese unilateral amputees as nonobese and four lean or wasted multiple amputees as obese. A correction of the BMI formula for amputation is feasible. Corrected BMI estimates, in contrast to uncorrected estimates, agree with FΔweight estimates. (Journal of Parenteral and Enteral Nutrition 18:355–358, 1994)