Validity of measuring knee-height as an estimate of height in diseased French elderly persons.

Body mass index is a tool to screen undernourished persons. Cut-off values of 22 or 24 kg/m2 are used for elderly persons. However, standing height cannot be measured in every elderly person. Knee-height has been proposed to estimate standing height, with equations derived from North-American people. The present study analyses the validity of these equations. Standing height and knee-height were measured in 126 elderly persons hospitalized in 6 French geriatrics wards. Consequences of using one of the either height was evaluated on body mass index, body surface area, and total body water as estimated from bioelectrical impedance measurements. Standing height and height derived from knee-height differed significantly by 0.9 cm (P=0.05). This has very limited consequences on the calculation of BMI (0.5 kg/m2), body surface area (0.04 m2) and on total body water (0.2 litres). A regression model was derived from covariates and found the same features as that in the model of Chumlea and Guo. In conclusion, knee-height can be used with sufficient accuracy as a surrogate for standing height in diseased French elderly persons.