From a healthcare professional: If a child's bone age is delayed, are they always a late bloomer?
While constitutional delay of growth, or being a "late bloomer" is a common cause of short stature, it should be considered a diagnosis of exclusion, first requiring ruling out other causes of short stature.
The first step to take when seeing a short child is to carefully measure them and be certain their height is plotted accurately on the correct age and sex growth chart.
The next step is to obtain the parental heights and calculate a mid-parental height (taking the average of the parent's heights in inches and adding on 2.5 inches for a boy and subtracting 2.5 inches for a girl). If the child is within the range of their mid-parental height, the child likely has familial short stature (assuming the parents did not have medical issues limiting their growth).
Plotting growth points and BMI
Another important step is to plot previous growth points. If the child has been growing at a normal growth velocity over time, pathologic causes of short stature are less likely. An abnormal growth velocity requires further work-up into endocrine (hypothyroidism, growth hormone deficiency, sex steroid deficiency, cortisol excess, etc.) and non-endocrine causes (cardiac, renal, hepatic, gastroenterologic, hematologic or other disease) of growth delay. Assessing the child's BMI or weight for height is also important, as insufficient calorie intake or calorie loss from issues such as malabsorption will also cause poor growth.
If a child's height is below what is expected for the midparental height, the growth velocity is normal, and there are no signs of other disease, the next step is to assess the child's degree of pubertal development and obtain a bone age. If the bone age and pubertal stage are delayed, the child would be expected to have a later puberty than average and catch up in height by growing longer than average. However, there are several caveats to the diagnosis of constitutional delay of growth.
If the predicted height based on the bone age is still below the height expected for the family, further work-up is still indicated. For example, a girl with Turner syndrome could have a delayed bone age due to lack of estrogen production, but her predicted height based on bone age is still likely to be low for the family.
Another caveat is the timing of puberty. A child with presumed constitutional delay of growth must continue to be followed, because if puberty comes earlier or occurs at a faster tempo than expected, the child may not achieve the expected adult height. In addition, it is important to make sure that puberty does actually occur and progress normally, as delayed puberty and absent puberty are difficult to initially distinguish.