Calcium
Also written as: Ca, total calcium, serum calcium
The blood level of calcium, a mineral tightly controlled by the parathyroid glands, vitamin D, and the kidneys.
What it measures
The total amount of calcium in the blood, including the portion carried on proteins such as albumin and the free portion the body actually uses. Blood calcium is kept in a narrow band by the parathyroid glands, vitamin D, the bones, and the kidneys.
Why a doctor orders it
It is included in routine metabolic panels because calcium is central to nerve, muscle, heart, and bone function. It is also checked when parathyroid, kidney, or bone problems are being considered, or when symptoms like fatigue, kidney stones, or muscle cramps are being worked up.
What is generally associated with a higher result
Broadly associated with overactive parathyroid glands, excess vitamin D, certain medications, and prolonged immobility. Mild elevations are also commonly a measurement effect - a prolonged tourniquet during the draw or dehydration can concentrate the sample.
What is generally associated with a lower result
Broadly associated with low vitamin D, low albumin (the carrier protein, which pulls the total number down without changing the usable calcium), kidney conditions, and low magnesium.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- The albumin level - low albumin lowers total calcium without affecting the active form
- A tourniquet left on too long during the blood draw
- Dehydration at the time of the draw
- Calcium or vitamin D supplements and antacids
- Some common medications, including thiazide diuretics and lithium
Questions to take to your appointment
- Was this result corrected for my albumin level?
- Would an ionized calcium test, which measures the free active form directly, be useful?
- Should parathyroid hormone (PTH) and vitamin D be checked alongside this?
- Could any of my supplements or medications be influencing it?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
Support this site
This site is free, has no paywall, and takes no money from hospitals, insurers, or billing companies. If it helped, a coffee keeps it going.
Buy us a coffee