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Phosphorus (Serum)

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 serum.

Quick summary

["Your blood phosphorus levels help assess bone health and kidney function."]

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

Key facts at a glance

LOINC
74889-7
Short code
Phosphate Sal-sCnc
Synonyms
Phosphate Sal-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 This Test Is Done

Doctors may order a serum phosphorus test to check for conditions affecting bone health, kidney function, or metabolic processes. It’s often used when symptoms like muscle weakness, bone pain, or abnormal lab results suggest an issue with phosphorus balance.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into a vein (usually in your arm) to draw blood. The process takes about 5 minutes, and you’ll feel a brief pinch. If you’re on blood thinners or have a history of bleeding issues, let your doctor know.

What the Results Mean

Phosphorus levels can vary based on diet, kidney function, and other health conditions. High or low levels may indicate problems like kidney disease, diabetes, or hormonal imbalances. Your doctor will interpret results in relation to your overall health and symptoms.

Common Conditions Affecting Phosphorus Levels

Conditions such as kidney disease (which affects phosphorus excretion), hypoparathyroidism (low thyroid hormone affecting bone metabolism), or certain cancers may alter phosphorus levels. Other factors like diet, medications (e.g., phosphate binders), or dehydration can also play a role.

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.

Clinical Significance

Short name

Serum Phosphorus Level

Frequently asked questions

What causes high phosphorus levels in the blood?
High phosphorus levels can result from kidney problems (where the kidneys can’t remove enough phosphorus), certain cancers, or overuse of supplements or medications that contain phosphorus. It may also occur in people with low levels of vitamin D or parathyroid hormone.
What causes low phosphorus levels in the blood?
Low phosphorus levels can be caused by malnutrition, excessive sweating, vomiting, or diarrhea, which lead to phosphorus loss. Certain medications, like antacids or diuretics, or conditions like diabetes, liver disease, or hyperparathyroidism can also contribute.
How often should I get this test?
Your doctor will determine how often you need this test based on your health status, symptoms, and other lab results. Regular monitoring may be needed if you have chronic kidney disease, diabetes, 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