5th April 2024

Investigations

In addition to serum phosphate levels, calcium, magnesium and plasma protein should be taken. In the presence of low phosphate:

• Hypercalcaemia indicates hyperparathyroidism
• Hypocalcaemia suggest malabsorption, vitamin D deficiency or hungry bone syndrome
• Hypomagnesemia suggests dietary deficiency 
• Paraproteinaemia should be suspected in severe hypophosphatemia with high globulins and suspicious features such as bone pain; hypercalcaemia, reduced renal function and anaemia. 

Other investigations include:

• Renal function – renal tubular disease or extra renal causes can cause electrolyte abnormalities
• Liver function may show raised alkaline phosphatase due to osteomalacia in chronic hypophosphatemia
• PTH and vitamin D levels 
• Arterial blood gas to check for respiratory alkalosis
• Plasma bicarbonate and urate, urine glucose and amino acids if considering Fanconi’s syndrome
• X Rays of affected joints – Looser zones suggest osteomalacia 
• Bone scintigraphy can show increased uptake in multiple areas in severe osteomalacia 
• Ultrasound neck or technetium 99mTc scan to identify enlarged parathyroid or ectopic glands
• Dual energy xray absorptiometry (DEXA) bone density scan as chronic hypophosphatemia will result in loss of bone density