BODY-MASS INDEX IN AMPUTEES

Whereas estimates of percent deviation of body weight from ideal (FDEL TAweight) are corrected for amputation, those of body mass index (BMI) are not, creating discrepancies in evaluating obesity. A correction o f the BMI formula for amputation is proposed. The formula for BMI was corrected for amputation mathematically. The mathematical model predic ts that the uncorrected BMI formula underestimates body fat in unilate ral amputees and overestimates body fat in subjects with bilateral amp utations at the same length of the legs. FDELTAweight and corrected an d uncorrected BMI estimates were computed in 15 subjects with unilater al leg amputation and in 8 subjects with multiple amputations. BMI est imates were as follows: in unilateral amputees, corrected 24.1 +/- 4.1 kg/m2, uncorrected 22.2 +/- 3.9 kg/m2 (P < .001); and in multiple amp utees, corrected 21.6 +/- 2.4 kg/m2, uncorrected 32.6 +/- 11.8 kg/m2 ( p = .043). Linear regressions of FDELTAweight obtained from standard n utrition assessment on FDELTAweight computed from uncorrected and corr ected BMI values were as follows: in unilateral amputees, uncorrected FDELTAweight = -0.079 + 0.932 X actual FDELTAweight, r = .974, p < .01 , and corrected FDELTAweight = 0.002 + 1.005 x actual FDELTAweight, r = .997, p < .01; in multiple amputees, uncorrected FDELTAweight = 0.52 8 + 1.930 X actual FDELTAweight, r = .607, p is not significant, and c orrected FDELTAweight = -0.010 + 0.920 X actual FDELTAweight, r = .936 , p < .01. Uncorrected BMI estimates erroneously classified two obese unilateral amputees as nonobese and four lean or wasted multiple amput ees as obese. A correction of the BMI formula for amputation is feasib le. Corrected BMI estimates, in contrast to uncorrected estimates, agr ee with FDELTAweight estimates.