How Is X-linked Hypophosphatemia Diagnosed?

Reviewed by: HU Medical Review Board | Last reviewed: July 2023

X-linked hypophosphatemia (XLH) is a chronic, progressive disease, so early diagnosis is important to stop symptoms from getting worse. XLH is diagnosed using a combination of blood, urine, and imaging tests. Sometimes a genetic test may be needed.1

These test results will help your doctor diagnose whether you or your child has X-linked hypophosphatemia or another condition that affects how the body processes phosphorus. An accurate diagnosis can help you get the right treatments sooner.1

Medical history and physical exam

Taking a medical history can be an important first step in diagnosing X-linked hypophosphatemia. The doctor will ask you about your overall health and any problems you have noticed. They will ask you whether people in your family have a history of rickets (bowed legs or knock knees caused by weak bones), short height, or fractures.1

Be ready to answer questions about:

  • Your diet
  • Any drugs or supplements you take
  • Allergies
  • Vaccine history
  • Alcohol and drug misuse
  • Your exercise habits

During a physical exam, a doctor checks your weight, height, heart rate, and blood pressure. They also look into your eyes and ears, look at your skin, feel the shape of some bones, listen to your heart and lungs, and press on your belly. They may ask you to walk or grip their hand.1

Blood tests

Your doctor may run several blood tests. These will check your overall health and rule out other conditions. A complete blood count (CBC) is a common blood test that measures red blood cells, white blood cells, platelets, and hemoglobin.2

A chemistry panel, or blood chemistry test, measures other aspects of your health. This test looks at things like kidney function, liver health, electrolytes, glucose, calcium, magnesium, and phosphorus. This test can be tailored to what your doctor needs to know.3

Your doctor will be looking for low phosphorus, Vitamin D, and calcium levels, and high levels of the hormone FGF23.1,4

Urine test

A urine test is also called a urinalysis. This test can be helpful to check for infections, kidney disease, diabetes, and the "phosphorus wasting" common in XLH.1

Imaging tests

Imaging tests can reveal signs of internal damage that low phosphorus levels may cause. Imaging tests to look for signs of XLH include:1

  • X-rays of the legs to look for signs of rickets (bowed legs or knock knees caused by weak bones) or fractures
  • X-rays to check for slow or uneven growth
  • Brain MRI skull to look for early fusing and dental problems
  • Ultrasound to check the kidneys
  • X-rays of joints to look for joint damage of the ankles, knees, or spine

Genetic testing

Genetic tests are blood tests that look at whether a change in your genes lead to X-linked hypophosphatemia. If there is no family history of XLH, a genetic test may be needed to confirm or rule out whether there is a mutation (change) in the PHEX gene.1

Anyone confirmed to have XLH should seek genetic counseling to help with family planning decisions.1

Hearing test

Hearing loss is a common complication XLH, so your doctor may order a hearing test.1

Things to consider

Remember, some tests may require you to wear certain clothes or not eat or drink for a few hours. Talk to your healthcare team about whether you or your child need to do anything to prepare for XLH tests.

While there is no cure for XLH, treatment is available to help reduce complications and preserve quality of life.

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