Hypophosphataemia

Hypophosphataemia is the term used to describe low levels of phosphate in the blood. It is most commonly caused by hyperparathyroidism and vitamin D deficiency.

Alternative names for hypophosphataemia

Hypophosphatemia

What is hypophosphataemia?

Hypophosphataemia is the name of a condition describing low levels of phosphate in the blood. Phosphate is an essential salt found in every cell of the body. Phosphate is also a component of our DNA and other key molecules within the body. It serves many important biological functions, for example releasing oxygen from red blood cells or producing energy for cell metabolism.

What causes hypophosphataemia?

Hypophosphataemia occurs when not enough phosphate is absorbed from the intestine into the bloodstream or when too much phosphate is passed in the urine, leaving low levels of phosphate in the blood. In some circumstances, hypophosphataemia can also occur when an excessive amount of phosphate moves from the bloodstream to inside the cells.

Phosphate is absorbed into the bloodstream from food in the small intestine. The blood is filtered by the kidneys and any surplus phosphate leaves the body in the urine. The amount of phosphate in the bloodstream is mainly controlled by parathyroid hormone, Parathyroid hormone causes the release of phosphate from the bones and stimulates the kidney to remove more phosphate from the bloodstream and into the urine. On the contrary, vitamin D helps both the kidney and the small intestine to reabsorb phosphate.

There are a number of conditions that result in hypophosphataemia, including:

  1. Primary hyperparathyroidism – this occurs when too much parathyroid hormone is produced. Parathyroid hormone stimulates the kidney to remove phosphate, resulting in reduced levels of phosphate in the bloodstream. This can happen when there is over growth and excessive function of one or more parathyroid glands.
     
  2. Secondary hyperparathyroidism – low levels of calcium in the bloodstream cause high levels of parathyroid hormone to be produced. The high levels of Parathyroid hormone stimulate the kidney to remove phosphate, leading to reduced levels of phosphate in the bloodstream.
     
  3. Vitamin D deficiency (rickets) – vitamin D helps the small intestine and the kidney to reabsorb phosphate back into the bloodstream. As a result, lack of vitamin D can result in low levels of phosphate in the bloodstream. Secondary hyperparathyroidismalso occurs in vitamin D deficiency, which in turn contributes to hypophosphataemia (as above).
     
  4. Hypophosphataemic rickets – a rare collection of inherited conditions that affects bones and growth.
     
  5. Kidney transplants – Post transplantation there is a reduction of renal tubular reabsorption: this means that more phosphate is lost in the urines and less is reabsorbed into the blood, causing hypophosphataemia. This phenomenon is usually temporary and limited to the post-transplantation period, however sometimes it can be long-lasting.
     
  6. Kidney damage occurring in conditions such as multiple myeloma, Wilson’s disease and systemic lupus erythematosuscan cause high levels of phosphate to be removed from the body by the kidney.
     
  7. Not enough phosphate in the diet – this is uncommon as phosphate is present in nearly all foods. However, some people have problems with absorbing phosphate from the diet.
     
  8. Treatment of diabetic ketoacidosiswith insulin can result in hypophosphataemia. Insulin increases uptake of phosphate into cells, leaving low levels in the bloodstream.
     
  9. Alcoholism – drinking too much alcohol on a regular basis can cause hypophosphataemia.

Hypophosphataemia can also occur in people with breathing difficulties or eating disorders, rare inherited conditions other than hypophosphataemic rickets, following gastro-intestinal surgery, side effects from certain medications, low blood magnesium levels, or high blood calcium levels.

What are the signs and symptoms of hypophosphataemia?

Low levels of phosphate rarely lead to symptoms of hypophosphataemia; rather symptoms usually result from the associated condition that causes hypophosphataemia. Very low phosphate levels can cause breathing difficulties, confusion, altered mental status, muscle weakness and muscle damage called rhabdomyolysis.

How common is hypophosphataemia?

This varies depending on the underlying condition. Mild hypophosphataemia is common; more severe forms of hypophosphataemia are much rarer.

Is hypophosphataemia inherited?

Hypophosphataemia itself is not inherited. However, an underlying condition that causes hypophosphataemia may be inherited. For example, hypophosphataemia may be due to excess loss of phosphate in the urine which can, very rarely, be due to a genetic condition.

How is hypophosphataemia diagnosed?

Hypophosphataemia is diagnosed using a simple blood test to measure phosphate levels, which can be carried out as an outpatient. Vitamin D, calcium and parathyroid hormone levels may also be measured at the same time. Depending on the results, further tests may then need to be carried out to determine the cause of the low phosphate levels.

How is hypophosphataemia treated?

Treatment should be aimed at the underlying condition and hypophosphataemia usually corrects with appropriate treatment. Vitamin D can be given in tablet or injection form, if required, and is often given with calcium supplements. If necessary, phosphate supplements can be given, either in tablet form or occasionally, through a drip.

Are there any side-effects to the treatment?

Phosphate given through a drip can sometimes cause low blood calcium levels (hypocalcaemia) and related problems, and therefore should only be given if absolutely necessary. Blood calcium and phosphate levels should be closely monitored. Tablet forms of supplemental phosphate can cause diarrhoea.

What are the longer-term implications of hypophosphataemia?

Hypophosphataemia is usually mild and can often be controlled by diet or lifestyle changes. Longer-term implications depend on the condition that caused hypophosphataemia. If the underlying condition cannot be stabilised and phosphate supplements are required, phosphate levels should be closely monitored.  

 

 


Last reviewed: Apr 2017