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Phosphorus (Serum/Plasma) Concentration

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of phosphorus, a mineral essential for healthy bones and cells, in your blood.

Quick summary

["Phosphorus levels help assess bone health and metabolic function."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
88713-3
Short code
Phosphate Stl-mCnc
Synonyms
Phosphate Stl-mCnc
Category
electrolyte
Sample
stool
Container
Clean container
Units
N/A
Ref low
2.5
Ref high
4.5
Critical range
1 N/A – —
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84100
Specimen volume
5 g
Stability
Refrigerated: 24h, Frozen: 7d
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test to check for conditions affecting phosphorus balance, such as kidney disease (where phosphorus builds up in the blood), bone disorders, or metabolic issues like diabetes or hyperparathyroidism. It can also help monitor treatment responses for conditions like hypophosphatemia or hyperphosphatemia.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood. Wear a loose shirt for easy access to your arm. If you’re on a 24-hour urine test for phosphorus, follow your doctor’s instructions for diet and fluid restrictions.

What Happens During the Test?

A healthcare professional will insert a small needle into a vein in your arm to draw blood. You may feel a slight pinch, but the procedure takes only a few minutes. If you’re nervous, let them know—they can offer options like numbing cream.

What Happens After the Test?

After the blood is drawn, the needle is removed, and a bandage is applied. You can return to your normal activities immediately. If you had a urine test, collect your sample in a sterile container as instructed.

Reference range

Adult: 2.5-4.5 mg/dLN/A

Specimen: stool

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Serum Phosphorus

Frequently asked questions

What Does a Low Phosphorus Level Mean?
Low phosphorus may signal conditions like malnutrition, kidney problems, or excessive sweating. It can also occur after certain treatments (e.g., dialysis, chemotherapy) or from medications like antacids or diuretics.
How Is Phosphorus Balanced in the Body?
The kidneys regulate phosphorus by filtering it out. Dietary sources (like nuts, seeds, or dairy) and vitamin D also play a role. If your levels are off, your doctor may adjust your diet, medications, or treatments accordingly.
Can Diet Affect Phosphorus Levels?
Yes! High-phosphorus foods (e.g., processed snacks, colas) can raise levels, while low-phosphorus diets (e.g., limiting nuts, dairy) may help if needed. Your doctor may recommend specific dietary changes based on your test results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy