Hypophosphataemia

Question 1

Major mechanisms of hypophosphataemia

Answer 1

​The three major mechanisms of hypophosphatemia are:

• 1. Redistribution of extracellular phosphate into cells (ECF to ICF)
• 2. Decreased intestinal absorption and
• 3. Depletion due to increased urinary loss

Question 2

Cause of Hypophosphataemia

Answer 2

Mnemonic: DR POLAH

• DKA (Diabetic Ketoacidosis)
• Refeeding syndrome (like in anorexia nervosa management)
• Primary hyperparathyroidism
• Osteomalacia
• acute Liver failure
• Alcohol excess
• Hyperventilation (painful venepuncture >> Hyperventilation >> low serum PO₄)

Question 3

Conditions that cause both hypomagnesaemia and hypophosphataemia

Answer 3

• Alcohol
• Refeeding syndrome/NG tube feeding/TPN

Question 4

Conditions that cause hypophosphataemia + metabolic acidosis + raised anion gap

Answer 4

• DKA
• Alcohol

Question 5

Effect of primary hyperparathyroidism on Ca and PO₄

Answer 5

Raised PTH → reduced PO₄, raised Ca

Question 6

Osteomalacia: Findings

Answer 6

Low Ca, and Low PO₄

Question 7

Hypophosphataemia: consequences

Answer 7

Haematological

• RBC haemolysis
• WBC and platelet dysfunction

​Neuromuscular

• CNS dysfunction
• Muscle weakness
• Rhabdomyolysis

Question 8

Patient with NG tube feeding >>> has the risk of ?

Answer 8

• PO₄: Low (Hypophosphataemia) (Mainly)
• Mg: Low (Hypomagnesaemia)

Question 9

When does refeeding syndrome occur?

Answer 9

When malnourished individuals are given nutritional support

OR simply recommence food intake

Question 10

Refeeding syndrome >>> who are at risk?

Answer 10

Individuals who have starved for 5days or more

Question 11

Refeeding syndrome: symptoms

Answer 11

• Weakness
• Alterations in mental state
• Neurological abnormalities
  
  • dysarthria
  • diplopia
• Rhabdomyolysis

Question 12

Triad of electrolyte abnormalities in refeeding syndrome

Answer 12

• PO₄: Low (Hypophosphataemia) (Mainly)
• Mg: Low (Hypomagnesaemia)
• K: Low (Hypokalaemia

Question 13

Refeeding syndrome >>> Management

Answer 13

• Correct electrolyte abnormalities (aggressively by IV or oral)
• Careful control of calorific intake:
  
  • Calorie intake may need to be reduced to >>> less than 50% (of the recommended amount)

​(Supplementary NG tube feeding, TPN etc. have no use here); they have their own complications

Question 14

Hypophosphataemia due to increased urinary loss/excretion

Answer 14

• Oncogenic hypo-phosphataemic osteomalacia
• X linked dominant: hypophosphataemic rickets