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Calcium ion concentration in serum/plasma

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

This test measures the amount of free (non-protein-bound) calcium in your blood, which is important for nerve and muscle function, blood clotting, and bone health.

Quick summary

["Free calcium levels help assess risks for conditions like low bone density or abnormal heart rhythms."]

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

Key facts at a glance

LOINC
10567-6
Short code
Citrate Smn-sCnc
Synonyms
Citrate Smn-sCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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, irregular heartbeat, or signs of low or high calcium levels. It’s also used to monitor conditions like kidney disease, bone disorders, or metabolic disorders that affect calcium balance.

What does the result mean?

Results help determine if your calcium levels are too high or too low. While exact ranges vary by lab, abnormal levels may indicate underlying health issues that need further evaluation.

How is the test performed?

A small blood sample is drawn from a vein, usually in your arm. The blood is processed to separate serum or plasma, where the ionized calcium is measured using a specialized lab technique.

What can affect test results?

Factors like recent calcium supplements, certain medications (e.g., calcium channel blockers), or dehydration can influence results. Avoiding calcium-rich foods or supplements for 24 hours before testing may help ensure accuracy.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Abnormally low ionized calcium (hypocalcemia) can cause muscle cramps, seizures, or abnormal heart rhythms. High ionized calcium (hypercalcemia) may lead to fatigue, kidney stones, or confusion. Both conditions require medical attention and often treatment adjustments.

Short name

Calcium (ionized)

Frequently asked questions

Why might my doctor ask for this test repeatedly?
If you have chronic conditions like kidney disease, hyperparathyroidism, or bone disorders, your doctor may monitor ionized calcium levels regularly to track changes and adjust treatments.
What if my test results are outside the normal range?
Your doctor will discuss the results with you and may recommend further tests or treatments, such as dietary changes, medication adjustments, or additional bloodwork to identify the cause.
Can diet or supplements affect this test?
Yes, consuming large amounts of calcium-rich foods or supplements before testing can skew results. Follow your doctor’s instructions to avoid interference, such as fasting or limiting supplements for a specified period.
  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