An abnormally low level of phosphate circulating in the blood (less than 0.7 millimoles/litre). It may be caused by reduced intake of dietary phosphate or intestinal MALABSORPTION SYNDROME, HYPERPARATHYROIDISM, leakage of phosphate through the kidneys, for example in heavy metal poisoning or diseases in which phosphate is excessively absorbed into bone, such as LEUKAEMIA and LYMPHOMA. There may be no symptoms or it may result in muscle weakness or bone pain. Severe cases may show signs of respiratory or heart failure.