Skip to content

Draft: not yet reviewed by a clinician

Use this page to prepare questions for your care team. It does not replace their advice. Your own targets and doses come from your nephrologist, diabetes team and renal dietitian.

Phosphate, calcium and PTH

In short

These three blood tests watch your bones and blood vessels. As the kidneys fail, phosphate builds up in the blood. The body answers by raising PTH (parathyroid hormone), which pulls calcium out of your bones and makes them weak. High phosphate and calcium can also form hard deposits in blood vessels, the heart, lungs and eyes (NKF). Doctors call this CKD-MBD (mineral and bone disorder). KDIGO recommends checking these tests from stage G3a on (KDIGO 2017, recommendation 3.1.1). The biggest thing you can do is cut phosphate additives, and take any binder with food.

Your numbers

Starting points, not your prescription

These numbers are typical starting points from guidelines. Your nephrologist, diabetes team and renal dietitian set your own numbers from your blood tests, urine output and medicines, and change them as your labs change. If your lab report or your team says something different, they win.

Test Typical range (your lab's range wins)
Phosphate (phosphorus) 2.5–4.5 mg/dL
Calcium (total) 8.8–10.3 mg/dL (MedlinePlus); many labs use a slightly different range
PTH, not on dialysis the best level is not known; your team acts if it keeps rising or stays above your lab's upper limit
PTH, on dialysis about 2–9 times your lab's upper limit
Alkaline phosphatase lab-specific; read with PTH
Test Typical range (your lab's range wins)
Phosphate (phosphorus) 0.81–1.45 mmol/L
Calcium (total) 2.20–2.58 mmol/L (MedlinePlus); many labs use a slightly different range
PTH, not on dialysis the best level is not known; your team acts if it keeps rising or stays above your lab's upper limit
PTH, on dialysis about 2–9 times your lab's upper limit
Alkaline phosphatase lab-specific; read with PTH

Sources: phosphate (NKF); calcium (MedlinePlus); PTH (KDIGO 2017, recommendations 4.2.1 and 4.2.3). PTH is reported in pg/mL or pmol/L, and each lab's test has its own range, so always compare with the range on your own report.

Working out "2–9 times". If your lab's upper limit were 65 pg/mL, 2–9 times would be about 130–585 pg/mL. Big changes inside that range also prompt a change in treatment (KDIGO 2017, recommendation 4.2.3).

How often (KDIGO 2017, recommendation 3.1.2):

Stage Calcium and phosphate PTH Alkaline phosphatase
G3a–G3b every 6–12 months depends on your first result –
G4 every 3–6 months every 6–12 months every 12 months
G5 and dialysis every 1–3 months every 3–6 months every 12 months, or more often if PTH is high

More often if a result is off or treatment changes. Vitamin D (25-hydroxy vitamin D) may also be checked (KDIGO 2017, recommendation 3.1.3). On hemodialysis, blood is tested every month (NIDDK); compare results taken at the same point, for example before a session.

Why they matter

  • Phosphate. Over months, high phosphate drives PTH up and calcium out of bone, and helps calcium deposit in blood vessels (NKF). People with these deposits are at the highest risk of heart disease (KDIGO 2017, recommendation 3.3.2).
  • Calcium. KDIGO suggests avoiding high calcium in adults (KDIGO 2017, recommendation 4.1.3). Calcium comes from food, from calcium-based binders and supplements, and from vitamin D medicines, so all of these count. About half of blood calcium rides on albumin, so a low albumin makes total calcium look low (MedlinePlus). The albumin test method matters too: in a study of about 500 people on hemodialysis, centers using one common method reported albumin about 6 g/L lower than centers using another, and their "corrected" calcium came out higher (de Roij van Zuijdewijn 2018; Serum albumin).
  • PTH. If PTH keeps rising, your team first looks for causes they can fix: high phosphate, low calcium, a high phosphate intake, and low vitamin D (KDIGO 2017, recommendation 4.2.1). On dialysis, PTH-lowering medicines may be added; surgery is for severe cases that do not respond (KDIGO 2017, recommendations 4.2.4–4.2.5).
  • After a transplant, phosphate is often low in the first months, and the advice can be to eat more phosphorus, not less (KDOQI 2020, statement 6.3.3).

What you can do

  • Cut phosphate additives first. Look for "PHOS" in the ingredient list (for example phosphoric acid or sodium phosphate). Up to all of the phosphorus in additives is absorbed, compared with 40–60 % from meat and less from plants, so this is the biggest lever (Noori 2010; KDIGO 2017, recommendation 4.1.8; Phosphate additives).
  • Take binders with food, every time you eat, meals and snacks, exactly as prescribed. A binder only works on phosphate that is in your gut at the same time (NKF).
  • Ask before taking calcium or vitamin D supplements: they add to your calcium (Supplements).
  • On dialysis, do every session in full: dialysis removes phosphate, and longer or extra dialysis is one way to treat stubborn high phosphate (KDIGO 2017, recommendation 4.1.9).
  • Keep protein up on dialysis by choosing foods with little phosphorus per gram of protein, such as egg whites and fresh meat or fish (Noori 2010; Phosphorus; Protein).
  • Track the trend. Treatment decisions are based on several results, not one (KDIGO 2017, recommendation 3.1.4).

In the app

Add a phosphate result under Labs (mg/dL or mmol/L). Above 4.5 mg/dL the app sets your phosphorus target to 800 mg a day, the low end of the guideline range; with a normal result it keeps 1,000 mg as a review ceiling; with a low result it sets no limit (design note 05; K/DOQI 2003). The app does not store calcium or PTH yet: use the lab tracker. Food warnings: Targets and warnings.

Examples

  • The hidden additives. On hemodialysis, Dee's phosphate is 6.1 mg/dL (1.97 mmol/L). Her dietitian finds processed cheese slices, deli ham and a dark cola each day, all with phosphate additives. Fresh chicken, home-made sandwiches and a clear soda replace them.
  • The skipped binder. Ray takes his binder with breakfast and dinner, but not with the large lunch he eats at work. The binder cannot work on a meal it never meets. Taking it with lunch fixes the gap.
  • High calcium. Pat's calcium is 10.6 mg/dL. Her team checks her calcium-based binder, her calcium supplement and her vitamin D medicine before changing anything.
  • Rising PTH. Before dialysis, Sam's PTH rises over three tests. His team checks phosphate, calcium and vitamin D first.

Ask your care team

  1. What are my phosphate, calcium and PTH, and which way are they heading?
  2. Do I need a phosphate binder? Which meals and snacks do I take it with?
  3. Is my binder calcium-based? Should I count it in my calcium?
  4. Should I take vitamin D or calcium supplements, or stop any I take?
  5. Is my vitamin D level checked?
  6. Can I see a renal dietitian about phosphate additives?

Get help now if…

These tests are rarely an emergency on their own.

Call 911 (or your local emergency number)

New confusion, a seizure, chest pain or fainting. See Get help now.

Call your care team today

If the lab or your team phones you about a very high or very low calcium or phosphate result, follow their instructions that day. Ask before you change any binder or vitamin D medicine.

Sources

Not yet reviewed by a clinician. Facts and sources last checked 2026-10-06.