# Situation: A nurse runs an adolescent-friendly health service at a Rural Health Unit (RHU) for clients aged 10 to 19 years who come for check-ups, school requirements, and counseling. An 11-year-old girl (11 years 0 months) has a body mass index (BMI) of 24.8 kg/m². On the World Health Organization (WHO) growth reference for children 5 to 19 years, her BMI-for-age z-score is +2.2. Using the WHO BMI-for-age cut-offs, how should the nurse classify her weight?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=629537  
> language: ko  
> subject: Nursing Practice II — Maternal and Child Health Nursing

## 문제

Situation: A nurse runs an adolescent-friendly health service at a Rural Health Unit (RHU) for clients aged 10 to 19 years who come for check-ups, school requirements, and counseling.

An 11-year-old girl (11 years 0 months) has a body mass index (BMI) of 24.8 kg/m². On the World Health Organization (WHO) growth reference for children 5 to 19 years, her BMI-for-age z-score is +2.2. Using the WHO BMI-for-age cut-offs, how should the nurse classify her weight?

## 보기

1. Obesity **✔ 정답**
2. Overweight
3. At risk of overweight
4. Normal

**정답: 1**

## 해설

For children and adolescents 5 to 19 years, the WHO reference classifies BMI-for-age above +1 SD as overweight and above +2 SD as obesity, so a z-score of +2.2 is obesity. Adult BMI cut-offs such as 25 kg/m² do not apply to children, which is why her BMI of 24.8 kg/m² can mislead. "At risk of overweight" (above +1 SD) and "overweight" above +2 SD are the categories for children under 5 years, a look-alike trap.

## 심화 해설

The classification of weight status in children and adolescents requires growth-chart-based interpretation rather than adult BMI thresholds. For an 11-year-old girl with a BMI of 24.8 kg/m² and a BMI-for-age z-score of +2.2, the correct classification is obesity.

Why the z-score, not the raw BMI, decides the category

In pediatric populations, body fatness normally changes with age and differs by sex. A single adult cut-off such as 25 kg/m² cannot capture whether a given BMI is high or low for a specific age and sex. The WHO growth reference for ages 5–19 years therefore expresses BMI as a BMI-for-age z-score (or standard deviation score). A z-score of +2.2 means the child's BMI is 2.2 standard deviations above the median for her age and sex, which crosses the +2 SD threshold for obesity.

WHO BMI-for-age cut-offs: 5–19 years versus under 5 years

The thresholds differ by age group, and this is a common source of confusion on licensure exams.

| Age group | Overweight | Obesity | At risk of overweight |
| --- | --- | --- | --- |
| 5–19 years (WHO growth reference) | > +1 SD (z-score > +1) | > +2 SD (z-score > +2) | Not used |
| Under 5 years (WHO child growth standards) | > +2 SD | > +3 SD | > +1 SD |

Watch out! The terms at risk of overweight and overweight shift meaning depending on the age group. For children under 5 years, overweight begins above +2 SD and obesity above +3 SD, with “at risk of overweight” occupying the +1 to +2 SD band. For the 5–19-year group, that same +1 to +2 SD band is simply called overweight, and above +2 SD is obesity. Because this client is 11 years old, the 5–19-year cut-offs apply, and +2.2 SD falls into obesity.

Why the raw BMI of 24.8 can mislead

If a clinician applied adult standards, a BMI of 24.8 kg/m² would be interpreted as normal or near-overweight. However, for an 11-year-old girl, a BMI of 24.8 is far above the age- and sex-specific median, which is why the z-score is the only appropriate metric for classification. The WHO approach avoids underestimating adiposity in children whose absolute BMI may still be below adult obesity thresholds.

Clinical relevance of accurate classification

Early identification of obesity in adolescence matters because it allows timely intervention before metabolic and cardiovascular complications become established. Different international definitions (WHO, IOTF, CDC) can produce different prevalence estimates and may not classify every adolescent identically . The WHO BMI-for-age z-score is widely used in primary care and school health settings because it is continuous, sex- and age-specific, and directly linked to the growth reference population. In the Rural Health Unit setting described, using the WHO chart ensures that a girl with a z-score of +2.2 is not mislabeled as merely overweight or normal based on adult intuition.

Key point! For ages 5–19 years, remember the simple rule: +1 SD = overweight and +2 SD = obesity. A z-score of +2.2 is above +2, so the classification is obesity, not overweight and not “at risk of overweight.”

## 임상 시나리오

Pediatric BMI-for-Age ClassificationUsing WHO growth reference cut-offs for ages 5–19 years
For children and adolescents aged 5–19 years, use the WHO growth reference and classify weight by BMI-for-age z-score, not by adult BMI cut-offs. A z-score of +2.2 is above the +2 SD threshold and is classified as obesity.

The cut-offs for ages 5–19 years are: overweight is a z-score above +1 SD, and obesity is a z-score above +2 SD. The category at risk of overweight is not used in this age group.

CautionDo not apply adult BMI thresholds such as 25 kg/m² to children. A raw BMI of 24.8 kg/m² may appear normal by adult standards but represents obesity when plotted on the pediatric growth chart. The under-5 cut-offs differ: overweight is above +2 SD and obesity above +3 SD.

## 핵심 개념

- **BMI-for-age z-score** — A measure of how many standard deviations a child's BMI is from the median for their age and sex, used to classify weight status in pediatric populations.
- **WHO growth reference (5–19 years)** — A growth chart reference for children and adolescents aged 5 to 19 years that classifies overweight as BMI-for-age >+1 SD and obesity as >+2 SD.
- **Obesity (pediatric)** — In the 5–19 year age group, defined as a BMI-for-age z-score above +2 SD; for children under 5 years, defined as above +3 SD.
- **At risk of overweight** — A category used only for children under 5 years, defined as a BMI-for-age z-score above +1 SD but not exceeding +2 SD.

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