Body mass index category code N[.N]

Identifying and definitional attributes

Metadata item type:Value Domain
METeOR identifier:311166
Registration status:Health, Standard 21/09/2005
Indigenous, Endorsed 13/03/2015

A code set representing categories of weight deficit/excess in adults and/or weight excess in children and adolescents.


In order to correctly categorise adults and children/adolescents, please refer to the categorisation protocol described under Guide for Use.

Representational attributes

Representation class:Code
Data type:Number
Maximum character length:2
Permissible values:
1Not overweight or obese < 25.00
1.1Underweight < 18.50 Low (but risk of other clinical problems increased)
1.2Normal range 18.50 - 24.99 Average
2Overweight >= 25.00 Average
2.1Overweight >= 25.0 Average
2.2Pre Obese 25.00 - 29.99 Increased
3Obese >= 30 Increased
3.1Obese class 1 30.00 - 34.99 Moderate
3.2Obese class 2 35.00 - 39.99 Severe
3.3Obese class 3 >= 40.00 Very severe
Supplementary values:
9Not stated/inadequately described

Collection and usage attributes

Guide for use:


Body mass index for adults cannot be calculated if components necessary for its calculation (weight or height) is unknown or has not been collected (i.e. is coded to 888.8 or 999.9).

BMI for adults is categorised according to the range it falls within as indicated by codes 1.1, 1.2, 2.1, 2.2, 3.1, 3.2, 3.3 or 9.9. For consistency, when the sample includes children and adolescents, adults can be analysed under the broader categories of 1, 2, 3 or 9 as used for categorising children and adolescents.


Body mass index for children and adolescents aged 2 to 17 years cannot be calculated if components necessary for its calculation (date of birth, sex, weight or height) is unknown or has not been collected (i.e. is coded to 888.8, 999.9 or 9).

Self-reported or parentally reported height and weight for children and adolescents should be used cautiously if at all.

To determine overweight and obesity in children and adolescents, compare the derived BMI against those recorded for the relevant age and sex of the subject to be classified, against Table 1: Classification of BMI for children and adolescents, based on BMI cut-points developed by Cole et al (see below). For example, an 11 year old boy with a BMI of 21 would be considered overweight (i.e. coded as 2), or a 7 year old girl with a BMI of 17.5 would be considered not overweight or obese (i.e. coded as 1).

Using this method, children and adolescents can only be coded as 1, 2, 3 or 9.

Collection methods:

Use N for BMI category determined (1, 2, 3 or 9) for persons (children and adolescents) aged 2 to 17 years.

Use N.N for BMI category determined (1.1, 1.2, 2.1, 2.2, 3.1, 3.2, 3.3 or 9.9) for persons aged 18 years or older.

Standard definitions of overweight and obesity in terms of BMI are used to derive age-specific and age-adjusted indicators of overweight and obesity for reporting progress towards National public health policy.

Relational attributes

Data elements implementing this value domain:

Person—body mass index (classification), code N[.N] Health, Standard 01/03/2005
Indigenous, Endorsed 13/03/2015