Body Mass Index (BMI) Measurement (Ambulatory) - CE/NCPD

ALERT

The body mass index (BMI) score may overestimate body fat in patients with muscular stature and underestimate body fat in older adults with decreased muscle tone.^{undefined#ref4">4} Take care to consider these situations when interpreting BMI scores.

OVERVIEW

BMI provides an estimation of body fat, resulting in a numeric score. The BMI is calculated by a formula using weight in kilograms and height in meters squared.³ The BMI score is then interpreted using the appropriate category range, which includes underweight (less than 18.5), normal (18.5 to 24.9), overweight (25.0 to 29.9), and obesity (30 and higher) (Table 1).⁵ Online calculators are available to input height and weight measurements for simplified results.

An increased BMI is associated with increased risk for cardiovascular diseases, dyslipidemia, diabetes, stroke, gallbladder disease, respiratory impairment, arthritis, mental illnesses, decreased mobility, cancer, and decreased quality of life.¹ Prevention of these diseases and risk reduction can occur with just 5% to 10% excess weight loss in those with higher BMI scores.⁵

The BMI score is calculated the same for both children and adults (Table 2), but the interpretation is different.² Adult BMI scores are not age or sex specific, unlike children and adolescents. The Centers for Disease Control and Prevention (CDC) growth charts contain BMI for age percentiles using age and BMI plot points for both male and female patients ages 2 to 19.² Obesity is defined as a BMI score at or exceeding the 95th percentile for children 2 to 19 years old.²

SUPPLIES

See Supplies tab at the top of the page.

EDUCATION

• Teach the patient how to interpret a BMI score.
• Encourage questions and answer them as they arise.

PROCEDURE

1. Perform hand hygiene before patient contact. Don appropriate personal protective equipment (PPE) based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
2. Introduce yourself to the patient.
3. Verify the correct patient using two identifiers.
4. Explain the procedure and ensure that the patient agrees to BMI measurement.
5. Ensure that evaluation findings are communicated to the clinical team leader per the organization’s practice.
6. Obtain the patient’s actual weight in kilograms.⁴ Stated, estimated, or historical weight should not be used.⁴ Enlist assistance from an additional health care team member if needed to ensure patient safety.
7. Obtain the patient’s actual height in meters. Do not rely on stated height because this could result in an inaccurate calculation.
8. Calculate the BMI score using online calculators or a mathematical formula (Table 2) per the organization’s practice. The BMI calculation may be done with online tools or with a mathematic equation using kilograms and meters squared.¹

   Ensure the correct measurement units are used depending on the method for calculating the BMI score per the organization’s practice.

9. Discard supplies, remove PPE, and perform hand hygiene.
10. Document the procedure in the patient’s record.

EXPECTED OUTCOMES

• Height and weight are obtained correctly for calculating a BMI.
• BMI is interpreted per child or adult categories.

UNEXPECTED OUTCOMES

• Patient’s weight exceeds the maximum capacity of the scale.

DOCUMENTATION

• Method of calculating patient BMI per the organization’s practice
• Patient’s BMI
• Education
• Unexpected outcomes and related interventions
• Evaluation findings communicated to the clinical team leader per the organization’s practice

PEDIATRIC CONSIDERATIONS

• Children and adolescents 2 to 19 years old² should have BMI interpreted using an age-appropriate growth chart.

OLDER ADULT CONSIDERATIONS

• Older adults may have decreased muscle tone and body fat that can be underestimated.

REFERENCES

1. Centers for Disease Control and Prevention (CDC). (2022a). Healthy weight, nutrition, and physical activity: About adult BMI. Retrieved November 30, 2023, from https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html (Level VII)
2. Centers for Disease Control and Prevention (CDC). (2022b). Healthy weight, nutrition, and physical activity: About child & teen BMI. Retrieved November 30, 2023, from https://www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/about_childrens_bmi.html
3. Centers for Disease Control and Prevention (CDC). (2022c). Healthy weight, nutrition, and physical activity: Body mass index (BMI). Retrieved November 30, 2023, from https://www.cdc.gov/healthyweight/assessing/bmi/index.html (Level VII)
4. Institute for Safe Medication Practices (ISMP). (2022). 2022-2023 Targeted medication safety best practices for hospitals. Retrieved November 30, 2023, from https://www.ismp.org/guidelines/best-practices-hospitals (Level VII)
5. National Institutes of Health (NIH), National Heart, Lung, and Blood Institute (NHLBI). (n.d.). Assessing your weight and health risk. Retrieved November 30, 2023, from https://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm (Level VII)

Elsevier Skills Levels of Evidence

• Level I - Systematic review of all relevant randomized controlled trials
• Level II - At least one well-designed randomized controlled trial
• Level III - Well-designed controlled trials without randomization
• Level IV - Well-designed case-controlled or cohort studies
• Level V - Descriptive or qualitative studies
• Level VI - Single descriptive or qualitative study
• Level VII - Authority opinion or expert committee reports

Clinical Review: Suzanne M. Casey, MSN-Ed, RN

Published: January 2024