Phosphorus (P)
Electrolytes & minerals ·Also called: PHOS, P, phosphate, inorganic phosphorus
What it is
Phosphorus works with calcium in bone and is central to how cells store and use energy. Healthy kidneys excrete the excess, so blood levels stay steady until filtration falls significantly.
Why your vet measures it
Rising phosphorus in kidney disease is not just a marker — it actively worsens the disease and drives the hormonal changes behind poor appetite and nausea. Phosphate binders and renal diets exist specifically to keep it down, and it is a value your vet will track at every recheck.
What a high result can mean
- Chronic or acute kidney disease
- Normal bone growth in puppies and kittens, which routinely sit above adult levels
- Vitamin D toxicity
- Haemolysis of the sample, which releases phosphorus from red cells
- A urinary obstruction
What a low result can mean
- Primary hyperparathyroidism
- Insulin treatment, particularly during treatment of diabetic ketoacidosis
- Long-term poor nutrition or malabsorption
- Some inherited kidney tubule disorders
Dogs and cats differ
A high phosphorus in a growing puppy or kitten is expected and needs no action — the bone is actively laying down mineral. The same value in a senior cat is a call to review the diet and consider a phosphate binder.
Questions worth asking your vet
- Does this level mean we should start a renal diet or a phosphate binder?
- What phosphorus target are we aiming for at my pet's kidney stage?
- Could my pet's age explain this?
Related terms
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