Why is FGF-23 (Fibroblast Growth Factor 23) High? Causes, Symptoms, and What to Do

Fibroblast growth factor 23 (FGF-23) is a hormone that plays a crucial role in regulating phosphate levels in the body. It is primarily produced by bones and works to lower phosphate levels in the blood. Understanding why FGF-23 levels might be high can help you better manage your health, especially if you have kidney issues or other related conditions.

What is FGF-23?

FGF-23 is a hormone secreted by bones. Its main function is to regulate phosphate and vitamin D metabolism. Phosphate is a mineral that helps build and repair bones and teeth, supports nerve function, and contributes to muscle contraction. FGF-23 reduces phosphate levels by decreasing its reabsorption in the kidneys and lowering the production of vitamin D, which in turn reduces phosphate absorption from the gut.

Why FGF-23 Levels May Be High

High levels of FGF-23 can occur due to several reasons:

• Kidney Disease: FGF-23 levels often rise in the early stages of kidney disease. As kidney function declines, phosphate accumulates in the body, prompting an increase in FGF-23 to try and lower these levels.
• Genetic Disorders: Certain genetic conditions can lead to high FGF-23 levels. These conditions often result in phosphate wasting, where the body loses too much phosphate through urine.
• Tumor-Induced Osteomalacia: This rare condition is caused by tumors that produce excess FGF-23, leading to low phosphate levels in the blood and weakening of bones.

Symptoms of High FGF-23 Levels

Symptoms associated with high FGF-23 levels are often related to low phosphate levels and may include:

• Muscle weakness
• Bone pain
• Fatigue
• Poor bone development in children

These symptoms can vary depending on the underlying cause and the severity of the phosphate imbalance.

How to Interpret FGF-23 Test Results

FGF-23 levels are measured in picograms per milliliter (pg/mL). The reference range can be assay-dependent, with intact FGF-23 levels typically up to around 60 pg/mL. It is important to note that there is no single adult reference range for this marker. Results should be interpreted in the context of individual health conditions and other lab results, especially phosphate levels and kidney function.

Frequently asked questions

What causes high FGF-23 levels in kidney disease? High FGF-23 levels in kidney disease are due to reduced kidney function, which leads to phosphate retention. The body increases FGF-23 production to help lower phosphate levels.

Can high FGF-23 levels be treated? Treatment focuses on addressing the underlying cause, such as managing kidney disease or treating a tumor. Phosphate supplements or dietary adjustments might be recommended if low phosphate levels are present.

Is FGF-23 testing part of routine blood work? FGF-23 testing is not typically part of routine blood work and is usually ordered when specific conditions, like unexplained low phosphate levels, are suspected.

When to see a doctor

If you experience symptoms like muscle weakness, bone pain, or fatigue, especially if you have a known kidney condition or a family history of genetic disorders affecting phosphate metabolism, it is important to discuss these symptoms with a healthcare provider. They can determine if FGF-23 testing or further evaluation is necessary.

Remember, this information is not a substitute for professional medical advice. Always consult with your healthcare provider for decisions regarding your health.