Growth measurements
Growth is primarily measured by height and weight. Adults should
be weighed using a beam balance with non-detachable weights. Infants are
usually weighed on a suspended scale. Height is typically measured with an
anthropometer that consists of a vertical and horizontal bar. Infants and
children under two years of age should be measured lying down for recumbent
length. For people with severe spinal curvature or those unable to stand,
knee height is used as a substitute measurement. Elbow breadth is
used as a measure of frame size and it is independent of age or weight; this
measure is of the distance between epicondyle of the humerus of the
right arm. Head circumference is a useful measure in infants and young
children as a measure of brain size.
Indices of growth
Growth indices use two or more measurements such as weight and height, or weight
and age. Weight-for-age is a useful index of acute malnutrition for
children 6 months to 7 years old. It reflects weight or body mass in relation
to other children of the same age and sex. Weight-for-age is also used to
assess protein-energy malnutrition. Weight-for-height is a sensitive
index of current nutritional status, reflecting weight in relation to other
children of the same height and sex, and is independent of age for children one
to ten years old. Height-for-age is an index of past or chronic
nutritional status. Height-for-age reflects height or linear growth in relation
to other children of the same age and sex.
Weight change is stable in healthy adults, usually no greater than 0.5 kg.
Severe starvation leading to death can occur at a 30% change in weight. Three
calculations of weight change can be made from the two measures of actual and
usual weight: percent of usual weight, percent of weight loss, and rate of
weight change.
Weight/height ratios are measures of weight corrected for height and are highly
correlated with obesity. Quetelet's index, which is weight in kilograms
divided by height in meters-squared, is commonly used as a measure of body mass
and is also referred to as body mass index (BMI). BMI is correlated with
percentage body fat and skinfold thickness and not correlated to height.
A BMI of 18.5-24.9 is normal according to the standards of the World Health
Organization. Patients with a BMI of under 18.5 are considered underweight;
those with a BMI 25-29.9 are defined as overweight; 30-34.9 indicates mild
obesity, 35-39.9 indicates moderate obesity, and 40 or greater indicates extreme
obesity.
