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Phosphorus (Phosphate) in Serum or Plasma

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

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

Quick summary

["Phosphorus helps maintain bone strength and supports normal cell function, but imbalances can affect energy and health."]

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

Key facts at a glance

LOINC
58019-1
Short code
Phosphate Fld.NB-mCnc
Synonyms
Phosphate Fld.NB-mCnc
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 Done

Your doctor may order this test to check for conditions affecting phosphorus levels, such as kidney disease (which often leads to low phosphorus), vitamin D deficiency, or certain metabolic disorders. It may also be part of routine monitoring for patients on medications that influence phosphorus, like certain diuretics or antacids.

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’s part of a broader metabolic panel. Bring any medications you’re taking to your appointment.

What the Test Involves

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but it typically takes only a few minutes. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results are compared to a general reference range for healthy adults, though exact values can vary by lab. Low phosphorus levels may indicate kidney problems or poor nutrient absorption, while very high levels could suggest overuse of certain supplements or conditions like tumor lysis syndrome.

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

Phosphorus Level

Frequently asked questions

What causes low phosphorus levels?
Low phosphorus can result from kidney disease (which fails to properly filter phosphorus from the blood), poor diet (low intake of foods like dairy, nuts, or seeds), excessive vomiting or diarrhea, or certain medications (e.g., antacids with aluminum or magnesium).
What causes high phosphorus levels?
High phosphorus is less common but can occur with kidney failure, certain cancers that release large amounts of phosphorus into the blood (e.g., lymphoma), overuse of phosphorus supplements, or untreated vitamin D deficiency.
How is phosphorus treated?
Treatment depends on the cause. For low phosphorus, your doctor may recommend dietary changes (e.g., fortified foods) or supplements. For high phosphorus, they might adjust medications, restrict phosphorus-rich foods, or recommend dialysis if kidney function is severely impaired.
  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