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Phosphorus, Serum or Plasma Mass 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 kidney function."]

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

Key facts at a glance

LOINC
35673-3
Short code
Phosphate ?Tm Ur-mCnc
Synonyms
Phosphate ?Tm Ur-mCnc
Category
electrolyte
Sample
urine
Container
Sterile urine 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
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order this test if you have symptoms like muscle weakness, bone pain, or kidney problems. It can also be part of routine checks for conditions affecting phosphorus balance, such as kidney disease or certain metabolic disorders.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a fasting protocol. Bring your test list and any medications to the appointment.

How the Test Is Performed

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a slight sting, but it usually takes only a few seconds. The blood sample is sent to a lab for analysis.

What the Results Mean

Results are compared to standard reference ranges, but exact values can vary by lab. High or low levels may signal underlying health issues, so discuss your results with your provider.

Reference range

Adult: 2.5-4.5 mg/dLN/A

Specimen: urine

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

How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Your provider will contact you once they’re ready.
Can I eat or drink before the test?
Follow your provider’s instructions—some labs require fasting, while others allow water or light snacks. Always confirm with your healthcare team.
What causes phosphorus levels to change?
Changes in phosphorus levels can stem from kidney function, diet (e.g., high intake of dairy or phosphate supplements), medications (e.g., antacids or diuretics), or metabolic conditions like diabetes or liver disease.
  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