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Serum Phosphorus (Phosphatase Activity) or Serum Phosphate Concentration

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

This test measures the amount of phosphate, a mineral essential for healthy bones, cells, and energy production, in your blood serum.

Quick summary

["Phosphate levels help assess bone health and metabolic function, but results alone don’t diagnose conditions without clinical context."]

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

Key facts at a glance

LOINC
14878-3
Short code
Phosphate Stone Ql
Synonyms
Phosphate Stone Ql
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 It’s Ordered

Your doctor may request this test if you have symptoms like muscle weakness, bone pain, or kidney issues, or if you’re being evaluated for metabolic disorders like hyperparathyroidism or phosphate disorders.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample drawn from a vein, usually in your arm. The test is quick and typically done in a lab setting.

What the Results Mean

Phosphate levels vary based on health, diet, and medical conditions. Your doctor will compare your results to your own baseline or lab-specific reference ranges to interpret them.

Common Conditions Affecting Results

Abnormal phosphate levels can signal kidney problems, bone diseases, or metabolic imbalances. High levels may indicate kidney failure or overactive thyroid, while low levels could suggest malnutrition or certain medications.

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 Phosphate

Frequently asked questions

What causes phosphate levels to be checked?
Your doctor may order this test if you have symptoms like fatigue, bone pain, or kidney problems, or if you’re being monitored for conditions like hyperparathyroidism, phosphate wasting syndromes, or metabolic bone diseases.
How is phosphate measured?
Phosphate levels are measured using an automated chemical method that detects phosphate ions in your blood serum. Results are reported in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L), depending on the lab’s standard.
Can diet affect phosphate test results?
Yes, phosphate levels can fluctuate based on diet—especially with high intake of foods like dairy, nuts, or processed foods. Avoiding phosphate-rich meals for 24 hours before testing may help stabilize results, but this isn’t always necessary.
  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