Possible causes of hyperphosphatemia include

• Advanced renal failure – GFR <30 significantly reduces the capacity to eliminate phosphate resulting in raised levels
• Inadequate renal excretion in the absence of chronic kidney disease also occurs in pseudohypoparathyroidism, hypoparathyroidism, and parathyroid suppression from hypercalcaemia due to vitamin A/D excess
• Phosphate overload from large transcellular shift of phosphate into the extracellular space that exceeds the kidneys ability to process it in a timely manner : tumour lysis syndrome, rhabdomyolysis, sepsis, DKA
• Excessive oral phosphate administration

Possible cause of hypophosphataemia  

Clinically significant acute hypophosphatemia occurs in relatively few clinical settings such as:

• Severe respiratory alkalosis
• After DKA treatment
• During carbohydrate refeeding in severely malnourished patients / starvation states / alcoholism patients
• In patients receiving TPN
• Severe respiratory alkalosis
• Acute alcohol use disorder
• Severe burns
• Long term steroid use