Bone age
29 December 2021

Bone age – check and grow

By Alan Rybczynski

Child’s growth depends on many factors, including bone age. Checking bone age is a recognized method to help assess final height. This simple test is used by pediatricians to diagnose short stature. When is it a good time to get tested, what does the measurement look like, and what does a delayed or accelerated bone age mean?

One child, three different ages

Record age – depends on the child’s date of birth.
Biological age – the child’s maturity level in relation to the developmental norm for a given population.
Growth age – the child’s height compared to the norms for a given population.

If a child has a growth deficiency, the growth age is lower than the calendar age. For example, a 7-year-old boy with a height of 110 cm (<3rd percentile). 110 cm is the median height for 5-year-old boys. Therefore, this boy’s height age is 5 years. The differences may be due to abnormal thyroid function, decreased growth hormone secretion, improper diet, Turner syndrome, pubertal disorders. Hyperthyroidism causes accelerated bone age, while hypothyroidism causes delayed bone age. Accelerated bone age is characteristic of accelerated puberty and slowed bone age is characteristic of delayed puberty.

When should the test be performed?

The test is recommended if you have growth disorders, e.g. you are too short (height below the 3rd percentile) in relation to your age. If, despite your tall parents, you grow slower than a child of short parents. Most often you will notice growth differences between peers at school. Pediatricians most often order this test to diagnose diseases associated with low growth. Determining your bone age will let you know if you should just watch how fast you grow and mature, or if you need to see an endocrinologist.
The test is also worth doing if you have pubertal disorders – premature signs of puberty (before age 8 in girls and before age 9 in boys) or delayed signs of puberty (no pubertal signs after age 13 in girls and after age 14 in boys).

How is bone age measured?

Measuring bone age using the Greulich-Pylea (GP) method is a non-invasive, safe and completely painless test. To determine the bone age, an X-ray is taken of the non-dominant hand and wrist (left for a right-handed person and vice versa). Then, on its basis, the specialist assesses the maturity of the child’s skeletal system. The examination should be performed by an experienced person, because the ossification nuclei in the wrist may appear out of synchrony and it is often not easy to match the X-ray picture with the scheme from the atlas. Then the doctor takes into account the ossification nuclei of the long bones of the hand.

How to interpret bone age assessment results?

Bone age can be consistent with metric age, delayed or accelerated by about a year.

Accelerated or concordant bone age

If a child has achieved an accelerated or calendar-concordant bone age and is characterized by low growth, he or she may achieve lower final height. In boys aged 16-18 years, in girls aged 15-16 years, this result usually indicates a completed growth process.

Retarded bone age

If a child turns out to have a delayed bone age by about 2-3 years, this often indicates genetically determined low growth combined with delayed puberty. This is already a better scenario than before, as the child may reach higher final height.

How often to check a child’s bone age?

Although the Greulich-Pylea bone age assessment is a safe test, it can expose the patient to a dose of x-rays. Doctors recommend performing this evaluation at least annually.


A bone age assessment is a useful test if you suspect you have a growth or pubertal disorder. With this diagnosis, your doctor is able to guide you on the right therapy to achieve a higher final height. It is also a clear signal for you to take care of the most important factors affecting growth, e.g. diet, sleep and physical activity.