A skinfold caliper is used to assess the skinfold thickness, so that a prediction of the total amount of body fat can be made. This method is based on the hypothesis that the body fat is equally distributed over the body and that the thickness of the skinfold is a measure for subcutaneous fat.
The sum of four skinfolds
To estimate the total amount of body fat, four skinfolds are measured:
- Biceps skinfold (front side middle upperarm)
- Triceps skinfold (back side middle upperarm)
- Subscapular skinfold (under the lowest point of the shoulder blade)
- Suprailiac skinfold (above the upper bone of the hip)
For this measurement the patient must be able to sit or stand in an upright position. Skinfold measurements are cheap, not very painful and easy to perform, although practice is required. With the table of Durnin en Womersly (1974), the percentage of body fat can be read by a given age and sex. This table contains data for people aged 17 years and older. More information on skinfold measurements can be found in this article.
Of all skinfold measurements, the triceps skinfold is the most reliable one to assess, because oedema is not often seen in the upper arm. The measurements are less reliable in elderly people, due to their weak skin and muscles. As a result, their muscles are often taken in the skinfold. Also in patients with chronic muscle diseases, dehydration and oedema, skinfold measurements can give unreliable values. Lastly, the measurements should be performed by a trained person; the accuracy of the measurements largely depend on the way they are done.
The triceps skinfold
The triceps skinfold is necessary for calculating the upper arm muscle circumference. Its thickness gives information about the fat reserves of the body, whereas the calculated muscle mass gives information about the protein reserves. A.R. Frisancho (1981) published tables showing percentiles for the thickness of the triceps skinfold. Below P15, the patient is malnourished. It's better to repeat the measurements for a good indication of changes in nutritional status and body fat mass.
For information about calculating the upper arm area, upper arm circumference, upper arm fat area, upper arm muscle area, go to the page on 'Anthropometry'. More information on skinfold measurements can be found in this document.