Bone Age Test: What the X-Ray Means for Your Child’s Height
A bone age test compares an X-ray of your child’s left hand with a reference atlas to estimate how mature the skeleton is. If the bone age is younger than the child’s real age, there is usually more growing time left; if it’s older, growth may finish sooner. It’s a clue for the doctor, not a verdict on final height.
Quick facts
- The test: one X-ray of the left hand and wrist, a few seconds, no needles, no fasting.
- How it’s read: most often against the Greulich and Pyle atlas, or by automated software.
- Delayed bone age: skeleton younger than calendar age; often means more growth time.
- Advanced bone age: skeleton older; growth plates may close earlier.
- Radiation: a very small dose; the doctor weighs it against the benefit, as with any X-ray.
What does a bone age X-ray actually show?
Children’s bones grow from soft plates of cartilage near the ends, called growth plates. On an X-ray they look like dark gaps. As a child matures, small wrist bones appear one by one, the ends of the finger bones change shape, and the gaps slowly narrow until they close after puberty. Once they’ve closed, height growth is over.
The radiologist lines up your child’s X-ray against standard pictures for each age and sex and picks the closest match. The report then prints two numbers: the chronological age (from the birth certificate) and the bone age (from the picture).
Bone age report: delayed vs advanced, what does it mean?
| Report says | Common reasons | What it can mean for height |
|---|---|---|
| Bone age matches real age | Normal timing; family short stature | Child likely to follow the family pattern |
| Bone age delayed | Late bloomer, poor nutrition, chronic illness, low thyroid, low growth hormone | More growth time ahead; cause matters |
| Bone age advanced | Early puberty, excess weight, some hormone conditions | Tall now, but growth may stop sooner |
Small differences mean little. Bone age readings vary between readers, and the Greulich and Pyle atlas was built from American children decades ago. A systematic review found it reads South Asian and other Asian boys as somewhat delayed in middle childhood compared with their true age. So “delayed by 1 year” in a healthy, steadily growing 8-year-old boy is often not a finding at all.
In a short child, a delayed bone age is often good news: the clock still has time on it.
Bone age delayed by 2 years: should I worry?
It depends on the growth curve, not the X-ray alone. The common, reassuring picture is the “late bloomer” (constitutional delay): a child who has always been on the short side, grows at a steady normal speed each year, often has a parent who started puberty late, and catches up in the late teens.
A doctor looks harder when the delay comes with a child who has slowed down or dropped across growth chart lines, has been unwell, is thin, tired, or has diarrhoea, or has other signs such as constipation, puffiness or very dry skin that may point to the thyroid. Then blood tests and a referral to a paediatric endocrinologist follow.
Can bone age predict final height?
Roughly. Doctors combine bone age, current height and sometimes parents’ heights in formulas that give a predicted adult height. These carry a margin of a few centimetres either way and are less reliable in children with medical conditions. Treat the number as a forecast, not a promise.
What to bring to the appointment
Measure both parents’ heights barefoot against a wall and write them down; the doctor uses them to work out your child’s target height range. Also bring every height you have on record (school cards, vaccination book, old clinic slips) with dates. A growth speed over a year or more tells the endocrinologist more than any single X-ray.
How does age change what the test is for?
- Under 1 year and 1 to 3 years: hand X-rays are less informative this young; other X-ray views are sometimes used, and doctors rely mainly on weight, length and head size charts.
- 3 to 6 years: used when growth is clearly slow or very fast, or signs of early puberty appear.
- Over 6: the most common age for the test, especially around expected puberty, to separate a late bloomer from a hormone problem, or to judge how much time is left when puberty starts early.
For everyday growth questions, our pieces on children’s height, genes and sleep and teen height, food and sleep cover what parents can actually influence. Puberty changes are covered in the puberty hygiene guide.
- Remove rings or bracelets from the left hand before the X-ray.
- Keep the hand flat and still for a few seconds; a parent can stand nearby with a lead apron if asked.
- Ask that the report states which method was used (atlas or software).
- Book the doctor review with the report, both parents’ heights and the past heights list.
- Don’t start any “height growth” powder, syrup or hormone without a paediatrician; many sold online make claims nobody has proven.
See a paediatrician promptly if a girl shows breast development before 8, or a boy shows genital or pubic hair changes before 9; if your child crosses down growth chart lines, stops growing for six months or more, or is much shorter than both parents would predict; or if poor growth comes with ongoing diarrhoea, weight loss, headaches with vomiting, vision changes or extreme tiredness. Headaches with vomiting or sudden vision problems need same-day care. Never give growth hormone, steroids or appetite syrups without a doctor’s prescription.
Bone age test questions parents ask
What does a bone age X-ray mean?
It shows how mature your child’s skeleton looks compared with standard pictures for their age and sex. The report gives the bone age next to the real age so the doctor can compare.
Is a bone age delayed by 2 years serious?
Not by itself. Many healthy late bloomers have this, but the doctor checks growth speed and general health to rule out thyroid, nutrition or hormone causes.
What does advanced bone age mean?
The skeleton looks older than the child, often with early puberty or excess weight. The child may be tall now but could stop growing earlier, so a doctor reviews the cause.
Can bone age predict height?
It gives an estimate, usually with a margin of a few centimetres. Predictions are less reliable in children with medical conditions.
Is a bone age X-ray safe for my child?
It uses a very small radiation dose for a single hand image, and doctors order it only when the result will guide decisions.
What is a normal bone age report?
One where bone age falls close to the child’s real age, within the normal variation the radiologist notes. Small gaps are common and usually unimportant.
Can my child grow taller if the growth plates are open?
Open plates mean growth is still possible, but how much depends on genes, health, nutrition and sleep rather than the X-ray.
Why is the left hand X-rayed?
The reference atlases were built on left hand images, so using the same hand allows a fair comparison.
Is the bone age test accurate for Pakistani children?
It is useful but imperfect. The main atlas was made from American children, and a large review found it can read Asian boys as slightly delayed, so small gaps deserve caution.
More report guides sit in Lab Reports Decoded.