Triusia assesses growth in children aged 0 to 60 months using the WHO Child Growth Standards 2006, adopted in Indonesia through Ministry of Health Regulation No. 2 of 2020 on child anthropometric standards. Besides the anthropometric indices, the calculator estimates weight age and height age, then compares both with chronological age to read the growth pattern.
Data entered
- Sex of the child.
- Date of birth and date of measurement.
- Weight in kilograms, to two decimal places.
- Recumbent length below 24 months or standing height from 24 months onward, in centimetres.
- Optional: head circumference, mid-upper arm circumference (MUAC), bilateral oedema, and birth weight.
Age
From version 5, age in days calculated from the birth and measurement dates selects the WHO LMS reference, as in WHO Anthro. Completed months are retained for reporting. If only age in months is known, days are estimated by multiplying by 30.4375 and the result is marked as approximate.
Measurement position adjustment
If a child under 24 months is measured standing, 0.7 cm is added. If a child aged 24 months or older is measured lying down, 0.7 cm is subtracted. Standing measurement below 9 months is treated as unusual, so no adjustment is applied and the record is flagged.
Z-score calculation
Z-scores use the LMS method: z = ((X / M)L - 1) / (L x S), where X is the child value and L, M, and S are the WHO reference parameters for the sex and the age or length of the child. Parameters come from the WHO tables by day for age-based indices and by 0.1 cm for length or height-based indices, with linear interpolation between two rows.
For weight-for-age, weight-for-length, weight-for-height, BMI-for-age, and MUAC-for-age, values above +3 or below -3 are recomputed using the distance between the 2 SD and 3 SD lines, following the WHO procedure. Length or height-for-age and head circumference-for-age use the basic formula. Results are rounded to two decimal places.
Nutritional status categories
| Index | Category | Z-score cut-off |
|---|---|---|
| Weight-for-age | Severely underweight | < -3 SD |
| Underweight | -3 SD to < -2 SD | |
| Normal weight | -2 SD to +1 SD | |
| Risk of overweight | > +1 SD | |
| Length or height-for-age | Severely stunted | < -3 SD |
| Stunted | -3 SD to < -2 SD | |
| Normal | -2 SD to +3 SD | |
| Tall | > +3 SD | |
| Weight-for-length, weight-for-height, and BMI-for-age | Severe wasting | < -3 SD |
| Wasted | -3 SD to < -2 SD | |
| Normal nutritional status | -2 SD to +1 SD | |
| Possible risk of overweight | > +1 SD to +2 SD | |
| Overweight | > +2 SD to +3 SD | |
| Obese | > +3 SD |
Head circumference below -2 SD or above +2 SD is flagged for evaluation. MUAC from 6 months of age is read against the 11.5 cm and 12.5 cm cut-offs.
Values that need rechecking
Following the WHO flagging limits, weight-for-age below -6 or above +5, length or height-for-age outside -6 to +6, and weight-for-length, weight-for-height, BMI-for-age, head circumference, and MUAC outside -5 to +5 are treated as implausible. The triage result then asks for the measurement to be rechecked. When bilateral oedema is present, weight-based indices are not computed.
Weight age, height age, and chronological age
Weight age is the age at which the median weight of the WHO reference child of the same sex equals the weight of this child. Height age is derived the same way from the median length or height. The median curve is joined at 24 months by converting standing height to recumbent length, then the age is found by interpolation between two adjacent days. A value below the median at birth is reported as 0 months, and a value above the median at 60 months is reported as more than 60 months.
Reading the pattern
Height age counts as lagging when it falls below chronological age by 10 percent or more. Weight age counts as lagging, or as ahead, when the gap against height age is 15 percent or more. Gaps below 0.5 months are ignored, and the pattern is not assessed below 1 month of age. An administrator can change all of these thresholds after expert panel review.
| Pattern | Meaning for triage |
|---|---|
| Weight age < height age < chronological age | Points to nutrition-related growth faltering. |
| Weight age equals height age, both below chronological age | Proportionally short. May be a normal variant or another cause. |
| Height age < chronological age, weight age > height age | Not typical of a nutrition problem. Another cause should be sought. |
| Weight age < height age, height appropriate for age | Weight lags first. Weight needs closer monitoring. |
| All three ages move together | No meaningful lag. |
Triage
The risk level is decided by rules stored in the system. Each rule holds one or more conditions. When several rules are met, the highest level applies and every reason is shown to the health worker. The default rules are built from the categories in Regulation No. 2 of 2020, the MUAC and oedema criteria in severe acute malnutrition management, and the three-age pattern. These rules are a first draft for expert panel review.
Repeat measurements
When a child has earlier measurements, the calculator computes the change in weight-for-age and length-for-age z-scores against a measurement at least 28 days earlier, and counts consecutive visits where weight gain falls below the minimum weight gain table for visits 21 to 45 days apart.
Verification of the engine
Version 5 technical checks matched all 24 z-scores from six WHO Anthro screenshots in the review document to two decimal places. The JavaScript and PHP engines returned matching results for 1,037 test cases, including the length/height transition and oedema. These checks verify the calculation implementation; clinical validation of triage remains part of the research.
References
- WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards: length/height-for-age, weight-for-age, weight-for-length, weight-for-height and body mass index-for-age. Methods and development. Geneva: World Health Organization; 2006.
- World Health Organization. WHO Child Growth Standards: head circumference-for-age, arm circumference-for-age, triceps skinfold-for-age and subscapular skinfold-for-age. Methods and development. Geneva: World Health Organization; 2007.
- Regulation of the Minister of Health of the Republic of Indonesia Number 2 of 2020 on Child Anthropometric Standards.
- Decree of the Minister of Health of the Republic of Indonesia Number HK.01.07/MENKES/1928/2022 on the National Clinical Practice Guideline for Stunting Management.
- Cole TJ, Green PJ. Smoothing reference centile curves: the LMS method and penalized likelihood. Statistics in Medicine. 1992;11(10):1305-1319.
- World Health Organization. anthro: Computation of the WHO Child Growth Standards. R package.