Investigating hypophosphataemia

摘要

A 5 5 year old man with a squamous cell carcinoma of the head and neck was investigated before referral for chemotherapy. He was asymptomatic and not taking any drugs. Blood test results showed phosphate 0.7 mmol/L (reference limit 0.8-1.5) and total calcium 2.34 mmol/L (2.15-2.60). The concentration of circulating phosphate depends on intestinal absorption, renal handling, and skeletal storage, and consequently is regulated by parathyroid hormone, vitamin D, and fibroblast growth factor 23. Internal cellular redistribution of phosphate is also important and results in hypophosphataemia under specific circumstances. The box outlines the causes of hypophosphataemia, based on the physiological regulation of phosphate metabolism. Chronic or mild hypophosphataemia (plasma phosphate 0.6-0.8 mmol/L; 1.86-2.5 mg/dL) maybe asymptomatic and therefore can be easily overlooked. A history outlining recent bone pain, muscle weakness, use of prescription drugs (including aminoglycosides, cisplatin, tenofovir), or exposure to toxins, heavy metals, or antacids containing magnesium, aluminium, and zinc, should be obtained. Inquiring about a family history of skeletal disease is important. Short stature skeletal deformities consistent with rickets, such as bowed extremities, widened wrists, cranial and chest deformities, or a familial history of hypophosphataemia or rickets should alert clinicians to a heritable cause. X linked hypophosphataemic rickets is, however, rare, occurring in 1 in 20000 live births but accounting for more than 80% of familial disease.