Conventional anthropometric prediction equations break down with altered relative body composition. For example, patients with advanced tuberculosis and cancer or with benign oesophageal stenosis may have similar BMIs as a result of weight loss, but muscle loss is likely to be greater in a cachectic inflammatory condition. Errors will therefore result from using the same body composition prediction equations. Illnesses that result in considerable loss of minerals or specific tissues, e.g. muscle wasting in patients with acquired immune deficiency syndrome (AIDS), may result in an overestimation of body fat using conventional prediction equations. In contrast, in patients with non-insulin-dependent diabetes mellitus (NIDDM) (Type 2 diabetes) who have increased intra-abdominal fat, there is underestimation of body fat using skinfold methods, which increases with the amount of central fat deposition (20). There is a problem in measuring body composition of amputees whose substantial absence of muscle mass gives unrealistic BMI values. In bed- or chair-bound patients, height measurement is not available for calculation of BMI. Alternative methods including arm span and lower leg length can be used to predict height with an accuracy within 4 cm (21).
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