Too much phosphate in the blood is known as hyperphosphatemia. The most common cause is kidney disease, but other conditions can lead to phosphate levels being out of balance.
Phosphate is a chemical found in the body. It contains a mineral called phosphorus that occurs naturally in many foods. Phosphorus supports bones and teeth to develop and helps turn food into energy for the body to use.
The kidneys naturally control levels of phosphates. However, if the kidneys are not working efficiently, they may not be able to remove enough phosphate, leading to high levels in the body.
Treatment for hyperphosphatemia will depend on the underlying condition. For people with kidney disease, a combination of diet and medication are used to keep phosphate levels under control.
Hyperphosphatemia does not usually have apparent symptoms. It is more likely that the symptoms of an underlying disease that can cause high phosphate levels, such as uncontrolled diabetes, are spotted first.
If levels of phosphate in the blood become too high, it may cause mineral and bone disorders and calcification.
Mineral and bone disorders
Bones need minerals and hormones to rebuild, grow, and stay strong. The kidneys balance the amount of phosphorus and calcium in the blood. If these are out of balance, it can draw calcium out of the bones and weaken them.
Because kidneys control the balance of minerals and other chemicals, chronic kidney disease can cause mineral and bone disorders. Those who have had kidney failure and are having dialysis are most at risk.
This deterioration can take place over many years, often without symptoms. But, as bones begin to get weaker, a person may start to feel pain in their bones or joints.
If this happens in children who have kidney disease, it can be more serious as their bones are still developing. Children who have mineral and bone disorder may not grow to full height. The bones in their legs may bend inward or outward, which is sometimes known as renal rickets.
Calcification happens when calcium is deposited in organs or tissues in the body. The condition can affect the veins and arteries and is known as vascular calcification. It is a particularly serious condition as the heart will need to work harder to pump blood around the body. Calcification can make dialysis more difficult.
High levels of phosphorus and calcium in the blood can also cause itchy skin and red eyes.
Kidney disease is the most common cause of hyperphosphatemia. Healthy kidneys adjust the levels of minerals in the blood, but kidneys that are not working properly are not always able to do this.
There are other conditions linked with high levels of phosphate in the blood, however, including the following:
- Uncontrolled diabetes: This causes high levels of blood sugar that can lead to serious medical problems, such as organ damage.
- Diabetic ketoacidosis: A complication of diabetes that can happen if the body begins to run out of insulin. Harmful ketones build up in the body and blood sugar levels rise.
- Hypoparathyroidism: A rare hormone disorder in which the body does not produce enough parathyroid hormone (PTH). PTH helps control the levels of phosphorus in the blood and bones.
- Hypocalcemia: Low levels of calcium in the blood.
Taking a phosphate supplement can also lead to hyperphosphatemia. Most people will get more than enough phosphorus from their diet, and the body is usually good at regulating levels. Nobody should take more than 250 milligrams (mg) of phosphorus supplements per day.
Processed foods often have phosphorus added to preserve them, and a high-protein diet may also contain more phosphorus than someone needs.
If someone has symptoms of hyperphosphatemia or a disease linked to the condition, they should see a doctor. The doctor will ask about their medical history, discuss any symptoms, do a physical examination, and sometimes recommend a phosphate test.
- Measuring the levels of phosphate in the liquid part of the blood, called plasma. The doctor will insert a needle into a vein in the arm and take a small sample of blood that will be sent to a laboratory for testing.
- A timed urine sample. A person will need to collect all of their urine over a set period, which is usually 24 hours.
- An X-ray may be needed if a person has symptoms of mineral and bone disorder. The X-ray will show any calcium deposits in organs or veins and any weakness or changes in the structure of a person's bones.
Typically, people with kidney failure have their phosphate levels regularly monitored, which means that hyperphosphatemia will usually be found during routine checks.
Treatment for hyperphosphatemia will depend on the underlying cause:
- If a person has uncontrolled diabetes, it is essential to bring this under control with diet, exercise, and a medicine called insulin.
- A person with the hormone disorder hypoparathyroidism may need to take a supplement. This will bring the levels of calcium and phosphate in the blood back to normal. A diet that is high in calcium and low in phosphorus can help to keep levels stable.
- When kidney disease causes hyperphosphatemia, a combination of changes to diet and medication is usually used to treat it. The primary aim is to prevent further damage to bones.
- A phosphate binder is a medication containing calcium. When taken with a meal, the drug controls the amount of phosphorus that the body absorbs from the food.
- Someone who has kidney failure will often need dialysis. This is a process to clean the blood of waste products and remove excess fluid if the kidneys are not able to do this. Kidney dialysis also removes some phosphates from the blood.
The main way to prevent hyperphosphatemia is to control the levels of phosphate and calcium in the body. This is usually done by eating certain foods and avoiding others.
Processed foods often contain phosphorus as a preservative, shown by ingredients that have the letters PHOS together. A person with an underlying condition linked to hyperphosphatemia may wish to avoid these foods.
Certain natural foods, such as peas, milk, and peanut butter, also contain high levels of phosphorus.
For people with kidney disease, eating a diet with the right amount of minerals is an essential part of managing the condition. This can be complicated, and a nutritionist can help to explain which foods to eat or avoid.
If kidneys are working normally and are producing the correct levels of hormones, the body will naturally balance levels of phosphate in the blood. If this is not happening, levels need to be regulated artificially using diet and medication.
Hyperphosphatemia can weaken bones and cause damage to veins, tissues, and organs in the body. It is crucial that people with kidney disease seek advice on diet to keep phosphate at a safe level, which can help to manage the condition.