Hypophosphataemia and Hypomagnesaemia

and Christopher Isles²

(1)

Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK

(2)

Dumfries and Galloway Royal Infirmary, Dumfries, UK

Q1 Where is phosphate found in the body, what is the usual daily intake and normal serum level?

About 85 % of body’s phosphorus is found in bone. The rest is stored intracellularly in tissues. It is therefore difficult to assess body stores from serum levels. Usual dietary phosphate intake is 30–50 mmol/day, mainly in dairy products. The reference range for serum phosphate in adults is 0.7–1.4 mmol/l.

Q2 Give the causes of hypophosphataemia

These can be considered under three headings, summarised in the box below.

Box 8.1 Causes of Hypophosphatemia

Inadequate intake e.g. poor diet from alcoholism, inadequate replacement during prolonged parenteral nutrition
Increased renal losses e.g. primary hyperparathyroidism, vitamin D deficiency, hypomagnesaemia
Transcellular shift e.g. refeeding syndrome, treatment of DKA, severe respiratory alkalosis,

Q3 How may hypophosphataemia present clinically?

Most patients with hypophosphataemia have no specific symptoms. When symptoms do occur then muscle weakness, bone pain, rhabdomyolysis, confusion and hallucinations are the most common presenting features. Serum PO₄ < 0.3 mmol/l is a medical emergency with risk of seizures, focal neurological deficits and heart failure, respiratory failure (due to weakness of the diaphragm), a proximal myopathy, dysphagia and ileus in addition to above.

Q4 When and how should hypophosphataemia be treated?
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