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Calcium, Ionized (Serum/Plasma)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of calcium that is electrically active (ionized) in your blood, which is important for nerve and muscle function.

Quick summary

["Ionized calcium helps regulate muscle contractions, nerve signals, and bone health."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
36074-3
Short code
CT Lower leg
Synonyms
CT Lower leg
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ct
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 doctor may order this test if you have symptoms like muscle spasms, numbness, or irregular heartbeat, or if you have conditions affecting calcium balance such as kidney disease, vitamin D deficiency, or certain medications.

What Does It Measure?

Ionized calcium is the form of calcium that is free in your blood and available for use by your body. Unlike total calcium, which includes bound forms, ionized calcium reflects the truly active level.

How Is It Collected?

A blood sample is taken from a vein, usually in your arm. The blood is drawn into a tube that separates serum or plasma from cells for testing.

What Are Common Causes of Abnormal Results?

Low ionized calcium (hypocalcemia) may be caused by conditions like hypoparathyroidism, kidney problems, or certain medications. High ionized calcium (hypercalcemia) could result from overactive thyroid, cancer, or prolonged exposure to sunlight.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Ionized Calcium

Frequently asked questions

What does an abnormal ionized calcium level mean?
An abnormal result may indicate an underlying health issue that needs medical evaluation. Your doctor will discuss your results in the context of your symptoms and other tests.
How often should I get this test?
The frequency depends on your health condition and medical needs. Your doctor will determine the best schedule for you based on your diagnosis and treatment plan.
Does fasting affect this test?
Fasting may not typically affect ionized calcium levels, but your doctor may still recommend fasting for other related tests. Always follow your healthcare provider’s instructions.
  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 16, 2026. · Read our editorial policy