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Phosphorus (Serum) Concentration

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

This test measures the amount of phosphorus, an essential mineral, in your blood serum. Phosphorus works with calcium to support healthy bones and teeth, as well as energy production in your cells.

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
22733-0
Short code
Phosphate Spec-sCnc
Synonyms
Phosphate Spec-sCnc
Category
electrolyte
Sample
serum
Container
Red-top tube (SST)
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 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order this test to check for conditions affecting bone metabolism, kidney function, or electrolyte balance. It can also help diagnose or monitor diseases like hypoparathyroidism, hyperparathyroidism, or metabolic bone diseases.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your provider specifies it, but this is not always required. Bring any medications or supplements you’re taking to your appointment.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but the process is quick and typically painless. The blood sample is then sent to a lab for analysis.

What Are Possible Results?

Results are reported as a concentration value (e.g., milligrams per deciliter, mg/dL). While reference ranges vary by lab, lower or higher-than-expected levels may signal underlying health concerns that need further evaluation.

Reference range

Adult: 2.5-4.5 mg/dLN/A

Specimen: serum

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 causes low phosphorus levels?
Low phosphorus levels can result from conditions like malnutrition, kidney disease, or certain medications (e.g., antacids or diuretics). Lifestyle factors, such as excessive alcohol use or prolonged fasting, may also contribute.
What are the symptoms of abnormal phosphorus levels?
Symptoms of low phosphorus may include muscle weakness, cramps, or fatigue. High phosphorus levels might cause bone pain, muscle spasms, or numbness. However, many people with abnormal levels may not experience noticeable symptoms until the condition worsens.
How often should I get this test?
Your provider will determine the frequency based on your health status, symptoms, or ongoing conditions. Regular monitoring may be recommended if you have chronic kidney disease, metabolic bone disorders, or other conditions affecting phosphorus metabolism.
  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