The present study of nursing home residents confirms studies showing a significant correlation between arm span and measured height and a highly significant correlation between BMI when measured by height and arm span, respectively [15–19]
. On average, the ratio between arm span and height was close to 1, which is comparable to a study among younger individuals (average 23 years) 
. The dispersion is, however, greater in the present population. This is most probably due to greater inter-individual variations in loss of stature in older persons 
. In addition, the ratio of BMIs based on arm span and height, respectively, was close to 1, but with rather great dispersion. By itself, reduction of stature leads to an increase in BMI. When calculating BMI the denominator is the square of height or arm span in metres. Changes in stature erroneously lead to a larger BMI index; an equivalent change in arm span does not occur 
. BMI calculations based on arm span are therefore likely to be more accurate.
Only a few of the participants in the present study were able to recall their historic height. One of them, an 86-year-old woman, reported a historic height of 1.66 m. Arm span was 1.69 m, and measured height was 1.43 m. Her weight was 51.0 kg. Based on the three measurements of height, BMI was 18.51, 17.86, and 24.94, respectively.
The WHO has established reference values for BMI: BMI ≥25 kg/m2
overweight, BMI 18.5–24.99 kg/m2
normal range, and BMI ≤18.49 kg/m2
. The references are considered to be relevant also “for the elderly”; however, it is stated that other cut-offs may be more appropriate for persons above 70 years of age 
. There is no clear BMI score which is agreed upon as a lower limit of the normal range, and reports on malnutrition in older people operate with various cut-off scores between 18.5 kg/m2
and 20 kg/m2
. Review of the literature indicates that the optimal BMI range for elderly people should be 24–29 kg/m2
. BMIs below and above these limits are for example associated with increase in mortality 
. A BMI of less than 24 kg/m2
is therefore considered an appropriate cut-off with regard to intervention in order to reduce nutrition-related complications 
. The cited studies are based on measure of height making some measurement bias likely as a result of stature decrease.
Several caveats must be considered when using BMI as a measure of nutritional state in a clinical setting. BMI says nothing about body composition, e.g. whether changes in BMI are a result of change in stature, muscle, or fat mass, or due to oedema. In daily work, additional information must be gathered, e.g. eating habits, medical condition, appetite, and drug use and weight changes. This has led to the development of more detailed assessment instruments for malnutrition. BMI is part of several of these instruments, for example the Mini Nutritional Assessment (long and short form) 
and Malnutrition Universal Screening Tool 
Although arm span usually remains stable throughout life, impaired movement in shoulder and elbow, and contractures may sometimes be a problem if both arms are affected.
Medical services in nursing homes are usually carried out by general practitioners. Nursing staff and physicians have an obligation to ensure that nursing home residents receive appropriate and timely care. The nursing home physician has the authority to carry out and to require assessments appropriate to ensure adequate medical services to the residents. Surveying nutritional state of the residents is a major task in this respect.