Calcium, Total and/or Ionized Blood Test
Measures the amount of calcium in blood. The order may include total calcium, ionized calcium, or both to help evaluate calcium balance.
["This blood test checks calcium levels, which are important for nerve, muscle, heart, and bone function."]
Key facts at a glance
- LOINC
- 61513-8
- Short code
- Y calcium alone or combined PhenX
- Synonyms
- Y calcium alone or combined PhenX
- Category
- liver
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 8.5
- Ref high
- 10.5
- Critical range
- 6 N/A – 14 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- phenx
- CPT
- 82310
- SNOMED
- 110744001
- 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
What is this test?
A calcium blood test measures how much calcium is present in a blood sample. Total calcium includes calcium bound to proteins, while ionized calcium is the free, active form that can be measured directly.
Why might I need this test?
Your clinician may order this test to assess calcium balance, investigate symptoms such as numbness, muscle cramps, weakness, confusion, or abnormal heart rhythms, or monitor conditions or medicines that can affect calcium.
How is the test performed?
A blood sample is collected and analyzed in the laboratory. Total calcium is usually measured in serum or plasma, while ionized calcium is generally measured in whole blood and may be checked promptly to limit changes caused by exposure to air.
How do I prepare for the test?
Follow the instructions provided with your lab order. Fasting is not always required, but certain medicines, vitamin D supplements, and conditions involving kidney function, parathyroid glands, or bone disease can affect the result; tell your clinician about relevant medicines and supplements.
Reference range
Adult: 8.5-10.5 mg/dLN/A
No special preparation required. Stay well hydrated.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
A high calcium result, called hypercalcemia, may be associated with conditions such as hyperparathyroidism, vitamin D excess, dehydration, or certain bone disorders. A low result, called hypocalcemia, may occur with low vitamin D, kidney disease, low magnesium, or certain medicines. If total calcium is unexpected, the clinician may consider an ionized calcium test and review albumin and other factors that can influence the result.
Short name
Calcium
Frequently asked questions
What is the difference between total and ionized calcium?
Do I need to fast before a calcium blood test?
Does a calcium test diagnose a specific condition by itself?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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