Hypophosphatemia
Hypophosphataemia is the name of a condition describing low levels of phosphate in the blood. Phosphate is an essential salt and is found in every cell of the body. Phosphate is a component of our DNA-(1)'>DNA and other key molecules within the body.; Iit serves many important biological functions, including for example releasing oxygen from red blood cells and producing energy for cell metabolism.
Phosphate is absorbed into the bloodstream from food in the stomachsmall 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 a number of hormones. pParathyroid hormone, which causes the release of phosphate from the bones and stimulates the kidney to remove more phosphate from the bodybloodstream into the urine. On the contrary, Vvitamin D, thyroxine and growth hormone all helps both the kidney and the small intestine to reabsorb phosphate.
Hypophosphataemia occurs either when not enough phosphate is absorbed from the stomach intestine into the bloodstream or when too much phosphate is passed in the urine, leaving low levels of phosphate in the blood. As third mechanism, hypophosphataemia can occur when an excessive amount of phosphate shifts from the bloodstream inside the cells.
There are a number of conditions that result in hypophosphataemia, including:
1. Primary hyperparathyroidism – this occurs when too much parathyroid hormone is produced from over growth and over excessive function of one or more of the parathyroid glands. Parathyroid hormone stimulates the kidney to remove phosphate, resulting in reduced levels of phosphate in the bloodstream.
2. Secondary hyperparathyroidism – low levels of calcium in the bloodstream cause high levels of parathyroid hormone to be produced. Parathyroid hormone stimulates the kidney to remove phosphate, resulting in 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, so lack of vitamin D can result in low levels of phosphate in the bloodstream. Secondary hyperparathyroidism also 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 – mild hypophosphataemia often occurs in kidney transplant patients.
6. Kidney damage occurring in conditions such as multiple myeloma, Wilson’s disease and systemic lupus erythematosus can cause high levels of phosphate to be removed from the body by the kidney.
7. Not taking 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 ketoacidosis with 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 stomach gastro-intestinal surgery, with certain medications, if blood magnesium levels are low, or if blood calcium levels are high.
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.
This varies depending on the underlying condition. Mild hypophosphataemia is common; more severe forms of hypophosphataemia are much rarer.
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.
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.
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.
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.
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.
British Thyroid Foundation may be able to provide advice and support to patients and their families dealing with hypophosphataemia.
Last reviewed: Mar 2019
