Phosphate

Also known as PO4, phosphorus, serum phosphate

HO₄P²⁻ inorganic ion

LOINC 2777-1 code verified serum mg/dL

What this substance is

formula: HO₄P²⁻
mass: 95.978 g/mol
monoisotopic: 95.96234
charge: -2
InChIKey: NBIIXXVUZAFLBC-UHFFFAOYSA-L
ChEBI: CHEBI:43474

Drawn from ChEBI's own curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Nothing here is hand-entered. Two masses are given because they answer different questions: the average is natural-abundance weighted and drives unit conversion; the monoisotopic value uses only the commonest isotope of each element and is what mass spectrometry measures.

3D model · Phosphate

Generated by RDKit from ChEBI's verified structure, and accepted only because its own 3D geometry reproduces ChEBI's InChIKey. A flexible molecule takes many shapes; this is one low-energy one. Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm. You may need to skip food and drink for a few hours first. Some medicines, vitamins and supplements can change the result, so tell your provider what you take. Do not stop any prescription medicine unless your provider tells you to.

Serum phosphate (inorganic phosphorus) is measured on a venous blood sample; a fast of several hours may be requested. Certain medicines, vitamins and supplements can affect accuracy and should be reviewed. A urine phosphate test may be ordered instead of or with the blood test.

Before the test

Fast (no food or drink) for several hours before the test if your provider asks.
Tell your provider about all medicines, vitamins and supplements, including over-the-counter ones.
Do not stop prescription medicines unless your provider tells you to.

Where: laboratory

Source: Phosphate in Blood -- MedlinePlus Medical Tests, U.S. National Library of Medicine cited · not yet checked by a person

In the lab

spectrophotometry

Ammonium molybdate (phosphomolybdate UV)

The machine mixes the blood sample with a chemical that grabs onto phosphate. The new compound soaks up ultraviolet light, and the more light it soaks up, the more phosphate is in the sample.

Inorganic phosphate reacts with ammonium molybdate in sulfuric acid to form an ammonium phosphomolybdate complex, read at 340 nm; absorbance is proportional to inorganic phosphate concentration.

Read by: Absorbance at 340 nm (secondary 700 nm)

What can throw it off

Haemolysis (positive interference above H index 300)
Liposomal drug formulations, e.g. AmBisome (falsely high)
IgM gammopathy (rare)

Why labs disagree: Normal phosphate depends on age: children's values run higher than adults', so a range depends on the age group it was set for. MedlinePlus also notes that normal ranges vary slightly among labs, and some labs use different measurements or test different samples.

Sources: NHANES 2017-2018 Laboratory Procedure Manual, Phosphorous, CDC/NCHS; Phosphorus blood test: MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine) cited · not yet checked by a person

What it reports on

nephron tubule regulated by
The kidneys mainly control blood phosphate by filtering out extra and holding back phosphate when it is low.
bone element stored by
Most of the body's phosphate is in the bones, combined with calcium.
parathyroid gland regulated by
The parathyroid glands make PTH, a hormone that helps balance phosphate and calcium in the blood.

Associated symptoms

Conditions this marker features in

When high

high Long-term reduced kidney function · monitoring
Checked regularly from CKD stage G3a onward; high phosphate is a known complication.

When low

low High blood calcium · supportive
Low phosphate with high calcium points towards too much parathyroid hormone, which makes the kidneys lose phosphate.
low Low vitamin D · supportive
Falls as raised parathyroid hormone makes the kidneys lose phosphate; this is the step that leads to rickets or osteomalacia.
low Overactive parathyroid gland · supportive
Usually in the low-normal range; some people have a low phosphate. It is part of the standard work-up.

Either direction

either Low blood calcium · supportive
Part of the first work-up, alongside calcium and parathyroid hormone. The guidance does not give a direction.

Ordered as part of

renal