15.2: Common Types of Anthropometric Measurements
By the end of this section, you will be able to:
- Describe the different scales used to obtain a patient’s weight
- Differentiate instruments used for measuring a patient’s height
- Identify normal and abnormal ranges for body mass index
A component of the generalized survey of patients is obtaining anthropometric measurement s. Consideration of individual circumstances will help the nurse determine which methods should be utilized to obtain these measurements. For example, a bedridden patient requires more assistance from healthcare professionals than would be needed for a mobile patient, and the nurse may need to use lifts, wheelchairs, and transfer device s. The nurse needs to not only obtain these measurements but also interpret their meaning. By analyzing the results, the nurse should be able to determine whether patients are underweight or obese and provide personalized care for them. However, it is more than just determining whether they are over- or underweight. Height is also used to assess growth trends (i.e., increased height in children or decreased height in older adults).
Weight Measurement
Weight is a crucial anthropometric measurement that is routinely assessed to provide information regarding health status, treatment effectiveness, and medication dosage s. Generally, in adulthood height changes very little, while weight can fluctuate due to a multitude of physiological conditions. Common physical conditions that require daily weight checks are cardiac, endocrine, and renal conditions. Mental conditions, such as depression , may also cause weight loss or weight gain. Frequent monitoring of weight can show the progress and effectiveness of the prescribed treatments.
See the competency checklist for Anthropometric Measurements. You can find the checklists on the Student resources tab of your book page on openstax.org.
Some medication dosages are dependent on an individual’s weight—for example, those prescribed as part of chemotherapy—and most pediatric medications are weight based. Depending on the setting (e.g., critical care versus an outpatient clinic) and patient condition, weight may be monitored daily, weekly, or just upon admission. Weight is also monitored at outpatient appointments. Patients with illnesses such as heart failure or kidney failure might have daily weight to monitor disease progression or management. Weight can be assessed using a variety of equipment, such as a traditional standing scale , a bed scale , a sling scale , and a bariatric scale .
Scenario: A nurse working at the family practice clinic escorts back a patient with a history of myocardial infarction and acute coronary syndrome. The patient is being seen for an annual physical.
Nurse: Good morning, Mr. Tanner. Before I bring you back to your room, I need to get your weight right over here.
Patient: Oh, I weigh myself weekly. I’m always between 220 to 225 lb (99.8 to 102.1 kg).
Nurse: That’s good to know. It sounds like you’re monitoring your weight regularly. Okay, go ahead and remove your coat and step up on the scale.
Patient: I already told you what I weigh. Why do I need to get weighed again?
Nurse: We just need an exact weight to monitor your health and response to treatment.
Patient: Okay, if you must.
Scenario follow-up: From this conversation, the nurse was able to communicate the importance of obtaining a weight prior to a healthcare visit.
Standing Scale
The standing scale is used for ambulatory patients (able to stand and/or walk) in a variety of settings, such as the healthcare provider’s office, long-term care facilities, hospitals, and homes. To use this scale, the patient will have to step up onto the scale and be stable without holding on to anything. With digital models, the weight will automatically appear. With manual standing scales, the nurse will need to adjust the sliding weights until the balance bar is level, as indicated by needle on the right side of most models (Figure 15.10).
Bed Scale
For patients who cannot stand or on bed rest, a bed scale may be used. These scales are embedded within most hospital beds. To use this type of scale, the nurse will need to “zero out” the bed, which must be done with the patient out of bed. Zeroing out the bed means that the weight of the bed with the linens is set to zero so that when the patient returns to the bed, the scale provides only the patient’s weight. This can be accomplished prior to admission, lifting the patient out of bed with a lift , or done while the patient is out of bed for toileting, procedures, or treatments.
See the competency checklist for Using a Portable Bed Scale. You can find the checklists on the Student resources tab of your book page on openstax.org.
Sling Scale
A sling scale is used for completely immobile or unsteady patients. A sling, or piece of large fabric, is placed under the patient, often by two healthcare personnel. Both ends of this fabric have a metal hook that connects to the sling scale. As the patient is lifted out of bed with this scale, weight is obtained. The sling scale is mostly used in long-term care settings and on acute inpatient units rather than in critical care settings. Even though many patients in critical care are immobile, the use of a sling scale would be difficult and even detrimental to use due to the multiple lines, tubes, and equipment needed for those patients.
Bariatric Scale
Sometimes patients do not fit into the traditional parameters of what a basic scale can measure, for instance, they may exceed the limit that can be measured, or do not fit in a particular area where the standing scale is stationed. In these situations, a specialized scale should be used to accurately measure the patient’s weight. Most acute care facilities are equipped with both traditional and bariatric scales. The bariatric scale is used for patients who weigh more than 350 lb (159 kg). Bariatric scales are wider and sturdier than traditional standing scales and can measure weight accurately to 1,000 lb (454 kg), or more.
Height Measurement
Height is another measurement that aids in developing a complete picture of the individual. When combined with the patient’s weight, it shows if the patient is underweight , overweight , or obese . A decrease in an adult’s height is also an indicator of bone degeneration , particularly of the vertebrae . For inpatient status, height is obtained just once, upon admission. Height is also checked yearly at primary care appointments.
Stadiometer
For most people, height is measured while the individual is standing using a stadiometer . The individual stands in front of the vertical stadiometer, back against wall, heels up against wall, head straight. The top horizontal bar will manually adjust to the individual’s height and rest on top of the head (Figure 15.11). When it is adjusted, the height measurement will be found near the top of the stadiometer.
Demi-Span for Bedridden Patients
For those individuals who are unable to use the stadiometer because of physical restrictions, a nurse can use a formula and the demi-span measurement to estimate the height. The demi-span is the distance in centimeters from the center of the suprasternal notch (Figure 15.12) to the tip of the middle finger while the arm is straight to the side at a 90-degree angle to the body. The measurement is then entered into one of the following formulas to determine the patient’s height.
Females: Height (cm) = (1.35 × demi-span [cm]) + 60.1
Males: Height (cm) = (1.40 × demi-span [cm]) + 57.8
Other less commonly used methods to determine height in bedridden patients include analyzing the knee height and analyzing the forearm length . The knee height, from the top of the knee to the sole of the foot, is measured in centimeters while the knee is flexed at a 90-degree angle. The forearm length, which is essentially the length of the ulna, is also measured in centimeters. These results are then entered into a formula to determine the height (RxKinetics, 2023).
Body Mass Index
The body mass index (BMI) is a value that is calculated from an individual’s height and weight. Computation of BMI begins at approximately two years old. To calculate BMI, the nurse must first obtain a patient’s weight and height. These numbers should then be placed into one of the following formulas:
Most healthcare charting systems will automatically calculate a patient’s BMI once the height and weight are entered. Multiple BMI calculators are also available on the internet, and BMI charts are located in many healthcare facilities to aid with this calculation (Figure 15.13). The nurse can also manually find the intersection of the height and weight on the chart.
BMI is then classified as underweight , healthy, overweight , obese , and severely obese. The healthy range for weight is a BMI between 18.5 and 24.9. A BMI below 18.5 is considered underweight, whereas a BMI of 25 to 29.9 is considered overweight. Obesity is defined as a BMI equal to or greater than 30, and severe obesity is a BMI equal to or greater than 40. It is important for the nurse to note that BMI can be impacted by the patient's background and activity, because body fat distribution differs by race and ethnicity, such as among Hispanic, Black, East Asian, and South Asian populations. Furthermore, BMI metrics are based on anthropometric measurements of White people. As a result, BMI should be used in conjunction with other assessment findings to recognize weight concerns. For example, muscle is more dense than fat. Therefore, a body builder may have the same BMI as someone who would be classified as “obese” according to the BMI calculation and not be truly considered “obese.”