Hyperphosphataemia

Hyperphosphataemia is defined by a serum phosphate concentration higher than 1.5 mmol/L. Delayed transport of samples to the laboratory can result in a spuriously elevated serum phosphate concentration.

Hyperphosphataemia is typically caused by:

• impaired kidney phosphate excretion (eg kidney disease, tumoral calcinosis, hypoparathyroidism)
• increased extracellular phosphate (eg rapid administration of phosphate, catabolic states, tissue or cell lysis).

Chronic kidney disease is the most common cause; hyperphosphataemia caused by kidney disease is usually chronic and asymptomatic. Clinical manifestations are usually related to associated hypocalcaemia and tetany. Chronic hyperphosphataemia is primarily treated by managing the cause. It can also include restricting phosphate intake, using phosphate binders and inducing diuresis (not recommended in patients with impaired kidney function). Specialist management is required.

Acute severe hyperphosphataemia (with electrolyte disturbance and sudden death) has been reported after taking preprocedural oral sodium phosphate laxatives (eg before a colonoscopy) (see Lavage solutions for colonoscopy in adults for more information). The rapid onset of hyperphosphataemia (in contrast to the chronic hyperphosphataemia seen with chronic kidney disease) causes cardiorespiratory collapse and seizures. Emergency treatment with volume expansion, and urgent haemodialysis, may be required.