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X-Ray Exam: Bone Age Study

Medically reviewed by: Larissa Hirsch, MD

What's an X-Ray?

An X-ray is a safe and painless test that uses a small amount of radiation to make an image of bones, organs, and other parts of the body.

The X-ray image is black and white. Dense body parts, such as bones, block the passage of the X-ray beam through the body. These look white on the X-ray image. Softer body tissues, such as the skin and muscles, allow the X-ray beams to pass through them. They look darker on the image.

X-rays are commonly done in doctors’ offices, radiology departments, imaging centers, and dentists’ offices.

What’s a Bone Age Study?

A bone age study helps doctors estimate the maturity of a child's skeletal system. They do this by taking a single X-ray of the left wrist, hand, and fingers. The bones on the X-ray image are compared with X-ray images in a standard atlas of bone development. The atlas is based on data from many other kids of the same gender and age. The bone age (also called the skeletal age) is measured in years.

Children’s bones have areas of new bone growth called growth plates at both ends. They add length and width to the bone. They can be seen on an X-ray because they're softer and contain less mineral, making them appear darker on an X-ray image than the rest of the bone.

Bones and growth plates change over time. As kids grow, their growth plates look thinner on X-rays and eventually disappear (called "closed growth plates"). Doctors assign a child’s bone age based on which standard X-ray images in the atlas most closely match how the child's bones look on the X-ray.

A difference between a child's bone age and their chronological age might indicate a growth problem. But perfectly healthy kids also can have bone ages that differ from their actual ages.

To do the study, your child will sit on a stool and place their left hand on the table with the fingers spread. They should stay still for 2–3 seconds so the X-ray image is clear. If the image is blurred, the X-ray technician might take another one.

Why Are Bone Age Studies Done?

The bone age study can help evaluate how fast or slowly a child's skeleton is maturing, which can help doctors diagnose conditions that slow down or speed up physical growth and development. This test is usually ordered by pediatricians or pediatric endocrinologists.

Bone age can be used to predict:

  • how much time a child will be growing
  • when a child will start puberty
  • what the child’s final height will be

The test also can help doctors monitor progress and guide treatment of kids with conditions that affect growth, including:

  • diseases that affect the levels of growth hormones, such as growth hormone deficiency, hypothyroidism, precocious puberty, and adrenal gland disorders
  • genetic growth disorders, such as Turner syndrome
  • orthopedic or orthodontic problems in which the timing and type of treatment (surgery, bracing, etc.) are guided by the child's expected growth

What if I Have Questions?

If you have questions about the bone age X-ray or what the results mean, talk to your doctor.

Medically reviewed by: Larissa Hirsch, MD
Date reviewed: March 2022