Discuss the theoretical basis and use of BMI percentile charts in the assessment of overweight and obesity in children and adolescents. Flashcards
Theoretical basis of BMI percentile charts – what are they, how are they developed, how
are they used.
BMI is calculated as:
BMI=Weight(kg)/Height(m2)
However, since children’s bodies develop at different rates during growth, their BMI is compared against age- and sex-specific percentile charts, which take into account these variations.
Development of BMI Percentile Charts
Population Data: BMI percentile charts are developed using longitudinal growth data collected from large population samples. These data are used to establish growth standards and norms for children and adolescents in specific age and sex categories.
**Percentiles: **Percentiles rank a child’s BMI in comparison to a reference population of the same age and sex. For example, a child with a BMI in the 85th percentile means their BMI is greater than 85% of children in the reference population.
Growth Reference Curves: The charts plot BMI on the vertical axis and age on the horizontal axis, with percentile curves showing BMI distribution. The most commonly referenced charts in the UK are based on World Health Organization (WHO) and UK90 growth reference data, while in the US, CDC growth charts are widely used.
Use of BMI Percentile Charts
Tracking Growth: BMI percentile charts are used to track a child’s growth over time, providing insight into their risk of developing overweight or obesity, or becoming underweight.
**Assessing Risk: **They help identify children who are at risk of developing health conditions associated with excess weight, such as type 2 diabetes or cardiovascular issues.
** How are they used?**
US - 85th = overweight, 95th = obesity
problem of over-estimating prevalence
* UK - 91st = overweight, 98th = obesity (clinical)
* UK – 85th, 95th (public health, prevalence, surveillance).
What is the relationship between their BMI percentile chart and other measures of growth?
Relationship with Other Measures of Growth
BMI percentile charts are often used alongside other growth measures to provide a more complete picture of a child’s overall health.
Height and Weight Percentiles: In addition to BMI percentiles, height-for-age and weight-for-age percentiles are used to assess whether a child’s growth is within normal limits.
**Head Circumference: **In infants and toddlers, head circumference is measured to assess brain development and growth.
**Waist-to-Height Ratio: **This can provide additional insight into central adiposity (fat distribution around the abdomen), which is associated with higher cardiovascular risk, especially in children with a BMI in the overweight or obese percentiles.
The use of multiple growth measures allows healthcare providers to identify children who may have a high BMI but are still growing proportionately in terms of height and other parameters.
**Consider critical evaluation **
Discuss strengths and limitations, sensitivity and specificity, how to improve the accuracy of assessment.
Critical Evaluation of BMI Percentile Charts
Strengths
Non-invasive and Easy to Use: BMI percentile charts provide a simple, non-invasive method for assessing a child’s growth in relation to their peers. They can be easily used in clinical and public health settings.
Standardized Approach: They provide a standardized reference for monitoring growth over time and can help identify deviations from normal growth patterns.
Screening Tool: BMI percentile charts serve as a useful screening tool for identifying overweight and obesity, which are risk factors for various health conditions.
Limitations
Not a Direct Measure of Body Fat: BMI does not directly measure body fat; it only provides an indirect estimate based on weight and height. It may overestimate fatness in muscular children and underestimate it in those with low muscle mass.
**Variability Across Populations: **BMI percentiles are developed based on reference populations, and their accuracy may be limited when applied to different ethnic or socioeconomic groups that were not well represented in the original data.
Sensitivity and Specificity: BMI percentile charts have low sensitivity for detecting fat distribution or central adiposity, which may pose greater health risks than overall body fat. They also lack specificity in distinguishing between children who are naturally large but healthy and those who are at risk for obesity-related conditions.
Improving Accuracy
Combining with Other Measures: To improve sensitivity and specificity, BMI percentiles can be used alongside other measures like waist circumference or body fat percentage. This can help identify children at higher risk of metabolic syndrome.
Ethnicity-Specific Standards: Incorporating ethnicity-specific or region-specific growth standards can improve the accuracy of assessments, as some populations tend to have different growth patterns and body compositions.
Discuss the types of percentile charts that are available.
There are several types of BMI percentile charts based on different datasets and growth references.
WHO Growth Standards: These charts are based on data from a multicenter study conducted by the World Health Organization (WHO) and are widely used for children from birth to 5 years old. WHO charts are also available for older children, and they focus on optimal growth patterns.
CDC Growth Charts: In the United States, the Centers for Disease Control and Prevention (CDC) provides growth charts for children aged 2–19 years. These charts are based on population data from the National Health and Nutrition Examination Survey (NHANES).
UK90 Growth Charts: The UK90 growth charts are based on a national reference dataset for children in the United Kingdom and are used in public health and clinical practice for children over the age of 2.
Specialized Growth Charts: There are also specialized growth charts for children with specific conditions, such as those with Down syndrome or cerebral palsy, who may have different growth trajectories compared to typically developing children.
