Anthropometric Measurement

Indications

The CHDP Program Health Assessment Guidelines (guideline #4) recommend anthropometric measurements in all children and adolescents at each preventive visit to ensure adequate growth patterns and to assess the risk of obesity. Accurate serial measurements over time are the most important aspect of anthropometry. Solitary deviations from a growth pattern curve can be a normal variant or due to an acute illness. However, according to the CHDP guidelines, steady change of the growth curve on serial measurements is a reliable indicator of an abnormal growth pattern and warrants further workup. For infants and toddlers under 2 years of age, weight, length, and head circumference are indicated by anthropometric measurements at each well-visit. Indicated measurements include weight and length for children over 2 years of age. BMI measurement is recommended for all children 2 years and older to determine adequate nutritional status and risk of obesity. These measurements should be plotted on World Health Organization (WHO) charts or the CDC charts, which are gender and age-specific to compare the child to the average population. In adults, anthropometric measurements are recommended at each well-visit to determine nutritional status and the risk of future disease. 

Contraindications

Anthropometric measurements are noninvasive and, as such, do not have any contraindications for their use. However, there are situations in which the measurements might give inaccurate results (such as acute illness) or be impossible to measure (such as a limb deformity or casting). Using anthropometric measurements in such situations can give falsely reassuring or alarming data and should be avoided. 

Equipment

Reliable and reproducible measurements are required to obtain meaningful data from anthropometric measurements. As such, clinicians should ensure the use of well-calibrated, quality equipment and check it regularly for accuracy. The typical equipment list required to obtain anthropometric measurements includes:

• Weight scale
• Calibration weights
• Stadiometer
• Knee caliper
• Skinfold calipers
• Nonstretchable tape measure
• Infantometer to measure the recumbent length

Technique or Treatment

Growth Charts

Isolated anthropometric measurements are not useful. The values obtained must be compared to relative standards for the appropriate population. The CDC charts are obtained from children raised in various nutritional conditions in the United States. The WHO charts outline the growth of healthy children under optimal nutritional and environmental conditions, providing a 'goal' standard for optimal growth.[5]

The CDC charts identify the normal growth pattern between the 5th and 95th percentiles. The 85th to 95th percentile is considered the overweight or at-risk category. The WHO charts are considered applicable to all children from birth to 5 years of age regardless of ethnicity, socioeconomic status, and type of feeding.[6] On WHO charts, the normal range is defined between 2 standard deviations above and below the mean or as z-scores between -2.0 and +2.0. This corresponds to a range between the 2nd and 98th percentiles. On the WHO charts, a BMI of +1 to +2 is considered the at-risk group for obesity. A comparison between the 2 charts showed that the WHO growth standards are less likely to classify a child as undernourished compared to the CDC charts.[7] This difference is due to the multinational data used to develop WHO charts, which included countries with a lower obesity rate than the US.[7]

When using growth charts, it is essential to use the correct chart for the patient's age and gender. It is also important to remember that children with disorders that alter the growth pattern need specialized plots to obtain meaningful results. Several specialized growth charts have been developed for children with Down syndrome, Turner syndrome, cerebral palsy, Williams syndrome, achondroplasia, Prader-Willi syndrome, and Rett syndrome. They should be used in place of standardized growth charts when indicated. The recommended technique for obtaining anthropometric measurements per CHDP guideline #4 is outlined below. 

Head Circumference

For infants and toddlers under 2 years of age, measure the largest circumference of the head using a nonstretchable measuring tape around the most prominent part of the head to the middle of the forehead. The tape measure should be pulled snugly around the head to compress the hair and underlying soft tissue. Repeat the measurement twice to obtain 2 readings within 0.2 cm or 0.25 inches. Record the average of the 2 closest measurements.

Recumbent Length

The recumbent length should be measured for infants and toddlers who cannot stand. Align the infant's head against the top of the headboard of the infantometer. An assistant must straighten the infant's body and legs, ensuring the feet are parallel to the footboard. Repeat the measurement twice to obtain 2 readings within 0.2 cm or 0.25 inches. The average of the 2 closest measurements should be recorded. 

Height

For children who can stand, a stadiometer should be used. The child should stand up straight, with buttocks, shoulder blades, and heels touching the back of the stadiometer. The feet should face outward at a 60-degree angle. If the patient has genu valgum, separate the feet to avoid overlapping the knees while maintaining contact between the knees. Arms should be loosely hanging at the sides with palms facing the thighs. The horizontal bar of the stadiometer should be lowered until the hair is compressed to the crown of the head. Remove any objects on the head and hair that may obstruct the bar from compressing the hair to the crown of the head. The measurement should be read to 0.1 cm or one-eighth of an inch. Repeat the measurement twice to obtain 2 readings within 0.2 cm or 0.25 inches. The average of the 2 closest measurements should be recorded. 

Weight

For children under 2 years of age, use a calibrated beam or a digital infant scale. Ensure the infant is not wearing any clothes and remove the diaper before measuring the weight. The weight should be measured to the nearest 0.01 kg or 0.5 ounces. For children older than 24 months, a balanced or electronic floor scale can be used.

BMI

BMI is a calculation based on the height and weight of the child and is recommended by the CHDP guidelines for all children older than 2 years of age. The formulas for the calculation of BMI in children are as follows:

• BMI = weight in pounds / [height in inches x height in inches] x 703
• BMI = weight in kilograms / [height in meters x height in meters]

In adults, BMI is used to diagnose obesity as it correlates with body fat. However, it does not directly measure body fat and has limitations when used in isolation. Percent body fat varies with age, gender, and ethnicity. Percent body fat increases with age even if the weight stays the same, making it a less accurate measure of obesity in adults. Also, in athletes, increased muscle mass for a given height and age increases their BMI, even though they have a very low percentage of total body fat.

Z-Scores

The American Academy of Pediatrics recommends using Z-scores to define malnutrition in children. This measurement uses standard deviations to determine a child's nutritional and developmental pattern compared to the average population. Z-scores are available for weight-for-height (WFH), weight-for-age (WFA), BMI for age, and head circumference measurements. Currently, z-score levels for classifying obesity in children are not well established. Consequently, they were not included in the CHDP guideline. 

Limb Measurements 

To measure upper leg length, have the patient seated with legs at a 90-degree angle. Then, run the measuring tape from the inguinal crease to the proximal aspect of the patella. To measure the upper arm length, find the superior edge of the spine of the scapula. Then, run the measuring tape down the center of the triceps to the olecranon. Immediately after measuring the upper arm length, the mid-point of the arm should be marked in preparation for measuring the mid-upper arm circumference (MUAC). The patient stands upright with the arm hanging freely at the side. The patient should not flex the arm muscles. Measuring tape should be placed snugly around the mid-point of the arm without compressing the skin.

Waist Circumference

Patients should stand with their arms crossed on the contralateral shoulders to measure waist circumference. The measuring tape should be placed snugly around the lateral aspect of each ilium at the mid-axillary line. It is an essential measure of anthropometry in adults and children as it directly measures central adiposity. Increasing central adiposity is associated with an increased risk of morbidity and mortality due to an increased risk of diabetes and heart disease.[2]

Skinfold Measurements

Common sites for skinfold measurements include the biceps, triceps, iliac crest, thigh, calf, subscapular, abdomen, and chest. The exact technique can vary, but we discuss one method using the triceps as an example. For the triceps skinfold, grab the skin 2 cm above the midpoint of the right upper arm with the thumb and index finger to create a skinfold. Then, place the calipers at the midpoint to obtain the measurement. Similarly, the skinfold measurement is obtained at other sites by grabbing the skin 2 cm away from the measuring site. Despite standard measuring techniques, skinfold testing has high variability and has limited use thus far in the clinical setting.

Complications

Errors in measurements are the only complications of anthropometric measurements. Evidence suggests that errors in weight and abdominal obesity measurements occur in higher proportions in the obese population.[8] This is possibly due to difficulty assessing bony landmarks in obese patients. Another common cause of measurement error is obtaining measurements in a nonuniform manner. Research shows classical anthropometric measurements, including weight, height, and BMI calculation, are less prone to measurement error.[9] Head circumference measurement, waist circumference measurement, and head-to-waist ratios have higher variability and are prone to errors.[9] Moreover, measurement errors only slightly improve after training. Sebo et al. studied the variability of these measurements when performed by general practitioners and noted an improvement after short theoretical and practical training.[10] A comparison of the 2 studies also reveals that the practitioners' experience does not improve or decrease the accuracy of these measurements.[9]

Clinical Significance

Anthropometric measurements have utility in assessing physical fitness data for a wide variety of the population, from children to elite athletes to the elderly. One study of Australian volleyball players revealed that anthropometric data improves with increases in playing level.[11] Another study used anthropometric measurements to determine physical fitness progress in women aged 60 to 100. Pilates and hydrogymnastics decreased BMI, weight, and hip-to-waist measurements.[12] Obesity is a major modifiable risk factor for cardiovascular disease, stroke, diabetes mellitus, dyslipidemia, and hypertension. One of the best clinical utilities of anthropometric data is to define obesity. The best measurement to define obesity is not uniformly agreed upon, as is illustrated by one study that compared BMI, waist circumference, waist-to-hip ratio, and waist-to-height ratio. This study found that there is not adequate evidence to support one method of measurement over any other, but states BMI is the most logical choice given its historical use. The authors also demonstrated that elevations in anthropometric measurements led to a higher odds ratio of dyslipidemia, hypertension, and hyperglycemia.[13]

The lengths of extremities are related to chronic diseases as well. A literature review shows that those with a shorter upper leg length (ULL) have a higher prevalence of metabolic syndrome.[14] Similarly, shorter upper arm length has an association with a higher prevalence of diabetes in Japanese Americans.[15]

Although anthropometric data in the adult population helps define obesity, it is also used extensively in the pediatric population to determine nutritional status. By measuring the height for age, weight for age, and weight for height over time, anthropometric measurements can help identify inadequate growth patterns warrant further evaluation.[1]

Head circumference is another anthropometric measurement routinely used in children. This measurement is important to diagnose microcephaly, which has well-documented complications. BMI calculations and z-scores can help identify obesity and malnutrition in children, leading to early identification and treatment.[1]

MUAC can help define malnutrition's severity. MUAC also has the utility of assessing nutritional status in the pregnant population, as one study showed that MUAC is the anthropometric measurement of choice in pregnancy.[4]

Although technology may eventually advance to replace anthropometry on some level, one study found that the anthropometric measures of waist and hip circumferences are superior to ultrasound in assessing regional adiposity.[16] A study from Sweden showed the association of anthropometrics with chronic medical conditions, measuring anthropometric measurements relative to underlying conditions such as myocardial infarction, congestive heart failure, stroke, cognitive impairment, and dementia.[2] It noted that participants with myocardial infarctions had significantly higher weight, BMI, and waist-to-hip ratio, indicating a higher subcutaneous and central adiposity prevalence. A high skinfold measurement was noted to be a strong indicator or predisposing risk factor for congestive heart failure in the study. Patients with cognitive impairment had a lower weight, and those with dementia were noted to have lower weight as well as lower skinfold measurements.[2] 

Enhancing Healthcare Team Outcomes

Anthropometric measurements are noninvasive and easily obtained, and they have a wide range of utility in pediatric and adult populations. In pediatric populations, it is an essential tool to detect metabolic and developmental abnormalities early on so that they may be addressed efficiently. In the adult population, they can be used to diagnose the severity of illnesses such as obesity and cognitive impairments and help follow patients over time to assess for improvement after treatment. Although an inherent measurement error exists, it can be minimized by using well-calibrated tools and training. To enhance long-term patient outcomes, an interprofessional team of nurses, nurse practitioners, physician assistants, and clinicians should work together to obtain reproducible results that apply to clinical settings consistently. This can help identify at-risk individuals early and help clinicians promote a healthy lifestyle for at-risk patients to avoid the well-documented adverse effects of obesity and malnutrition.