Phosphate
Serum Phosphate
What this test measures
Phosphate is a mineral that works with calcium to build strong bones and teeth. It also helps your body make energy and is important for muscle and nerve function.
Understanding the numbers
Typical range: 0.8-1.5 mmol/L
Phosphate levels are closely linked to calcium, vitamin D, and kidney function.
- Low: 0.2–0.8 mmol/L
- Normal: 0.8–1.5 mmol/L
- Raised: 1.5–2.5 mmol/L
- Markedly raised: 2.5–3.0 mmol/L
Key numbers
- 0.8 mmol/L — Lower limit
- 1.5 mmol/L — Upper limit
- 1.8 mmol/L — CKD — target to stay below
Typical UK range. Phosphate is tightly linked to calcium and vitamin D. Raised phosphate is usually a sign of impaired kidney clearance in CKD. Low phosphate occurs in refeeding syndrome, severe alcohol withdrawal, diabetic ketoacidosis recovery, and in rare renal phosphate wasting.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- Most commonly caused by kidney disease
- Can be caused by an underactive parathyroid gland
- May cause itching, joint pain, or muscle cramps
- High phosphate with high calcium can lead to deposits in blood vessels
Questions you could ask your GP
- What is causing my abnormal phosphate level?
- Do I need my kidney function or parathyroid checked?
- Should I change my diet or take supplements?
- Is this related to my vitamin D or calcium levels?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
CKD — raised phosphate
Miriam has CKD stage 4 (eGFR 22). Phosphate 1.9, calcium 2.3, PTH raised.
What the GP said: “Your kidneys aren't clearing phosphate well. We'll start a phosphate binder with meals and reduce dairy and processed foods a bit. The goal is to keep phosphate under 1.8 to protect your bones and blood vessels.”
What happened next: With sevelamer and dietary advice, her phosphate dropped to 1.6 over three months.
Raised phosphate in CKD is treated with phosphate binders taken with meals and dietary moderation. Uncontrolled phosphate drives vascular calcification and worsens cardiovascular risk.
Refeeding syndrome — severely low phosphate
Dileep had been severely underweight and was started on nutritional support three days ago. Phosphate fell to 0.28, potassium and magnesium also low.
What the GP said: “This is refeeding syndrome — as we restart nutrition the body shifts phosphate, potassium and magnesium into cells quickly, leaving the blood low. We need to slow the feeding and replace all three, with a dedicated refeeding protocol.”
What happened next: With IV replacement and slower feeding, phosphate came up over five days without cardiac complications.
Refeeding syndrome is a genuine emergency. Anyone malnourished or after prolonged starvation who restarts eating is at risk — phosphate, potassium and magnesium must be checked and replaced before aggressive feeding.
DKA recovery — falling phosphate
Kyle was being treated for diabetic ketoacidosis. At 24 hours his phosphate had dropped to 0.54.
What the GP said: “As insulin drives sugar into cells, it also pulls phosphate in — a known drop during DKA recovery. We'll replace it and keep an eye on it for the next 24 hours.”
What happened next: With oral replacement phosphate rose to 0.9; Kyle recovered from DKA.
Expected phosphate drops in DKA treatment are routinely watched. Replacement is not always needed if mild, but deeper drops warrant treatment.
Hyperparathyroidism — phosphate at low end
Ava had raised calcium 2.78 with PTH 11. Phosphate was at the low end at 0.75.
What the GP said: “Primary hyperparathyroidism often pushes phosphate down at the same time as raising calcium. Surgery is usually the definitive treatment.”
What happened next: Parathyroidectomy corrected calcium and phosphate.
PTH causes phosphate loss in the urine. Raised calcium with low-ish phosphate is the 'hyperparathyroid signature'. Picking up both together sharpens the diagnosis.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.