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Phosphorus (Serum) – 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 serum.

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
14407-1
Short code
Phosphate Gast-mCnc
Synonyms
Phosphate Gast-mCnc
Category
electrolyte
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
1 N/A – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
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 hypophosphatemia (low phosphorus) or hyperphosphatemia (high phosphorus).

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 instructed. Bring any medications or supplements you’re taking, as they may affect results. Avoid strenuous activity the day of the test.

How the Test Is Performed

A blood sample is drawn from a vein, typically in your arm, by a healthcare professional. The sample is sent to a lab for analysis using an enzymatic method to measure phosphorus concentration.

What the Results Mean

Results are compared to standard reference ranges, but exact values can vary by lab. Low levels may indicate conditions like malnutrition, kidney disease, or certain medications. High levels could signal overuse of phosphate supplements, kidney problems, or metabolic disorders.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

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 (hypophosphatemia) can result from conditions like malnutrition, excessive vomiting or diarrhea, overuse of antacids or laxatives containing phosphate, or certain medications. It may also occur in people with kidney problems or those who’ve had prolonged bed rest.
What causes high phosphorus levels?
High phosphorus (hyperphosphatemia) can stem from kidney failure, overuse of phosphate supplements or laxatives, or conditions like hypoparathyroidism (low thyroid hormone affecting calcium). It may also appear in people with certain cancers or severe dehydration.
How is phosphorus level monitored?
If your phosphorus levels are abnormal, your doctor may recommend dietary adjustments (e.g., limiting phosphate-rich foods), medications to regulate levels, or further testing to identify the root cause. Regular follow-ups may be needed to track changes.
  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