Validity of equations using knee height to predict overall height among older people in Benin

Objectives: Chumlea's formulas are a validated means of predicting overall height from knee height (KH) among people >60 y of age, but, to our knowledge, no formula is validated for use in African countries, including Benin. The aim of this study was to compare height provided by predictive formulas using KH to measured height in an elderly population in Benin.

Methods: Individuals >60 y of age in Benin underwent nutritional assessment with determination of weight, body mass index (BMI), height, and KH. A Bland-Altman analysis was carried out by sex and age. The percentage of predictions accurate to ±5 cm compared with the measured height was calculated. The tested formulas were Chumlea's formulas for non-Hispanic Black people (CBP) and two formulas for use among Caucasians.

Results: Data from 396 individuals (81.1% male) were analyzed. The three formulas achieved 98% accuracy, but with 4.6% risk for error (±2 SD: -6 to +9 cm), which appeared to make them unfit for the whole population. Nevertheless, if a level of prediction ±5 cm is considered acceptable in clinical practice, the CBP formula achieved 83.1% accuracy. Moreover, there was no significant difference in BMI calculated with the measured and the predicted height, and the nutritional status based on BMI did not differ.

Conclusion: CBP formulas seem applicable in 83% of cases (±5 cm) to assess the height with KH of older people in Benin and do not overestimate the prevalence of malnutrition.