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.
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:
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.
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.
Last reviewed: Apr 2017