P-Calcium is a blood test that measures the total concentration of calcium in plasma. Calcium is a vital mineral that is needed for bone structure, muscle function, nerve signaling, heart rhythm and blood coagulation.
Around 99 percent of the body's calcium is stored in the bones and teeth. The smaller amount that circulates in the blood is carefully regulated by an interaction between the parathyroid glands, bones, kidneys and intestines. The regulation is primarily influenced by parathyroid hormone, PTH, and vitamin D.
What does a P-Calcium test show?
P-Calcium shows the total amount of calcium in plasma. Calcium in the blood occurs in different forms. About half is free, so-called ionized calcium, while the rest is mainly bound to the protein albumin or to other substances in the blood.
Ionized calcium is the biologically active form and is directly involved in, among other things, muscle work, nerve signaling and the electrical function of the heart. Since P-Calcium also includes protein-bound calcium, the result can be affected by the albumin level.
Why is calcium in the blood analyzed?
The analysis is used to detect and monitor disorders in the body's calcium balance. A P-Calcium test may be relevant, among other things, if there is suspicion of:
- over- or under-function of the parathyroid glands
- vitamin D deficiency or excessive intake of vitamin D
- kidney disease
- osteoporosis or other effects on the skeleton
- kidney stones
- certain cancers
- unexplained fatigue, muscle weakness or neurological symptoms
- drug treatment that can affect calcium balance
What does an elevated calcium level mean?
An elevated calcium level is called hypercalcemia. Common underlying causes are over-function of the parathyroid glands and certain cancers. Hypercalcemia can also occur with, for example, high intake of calcium or vitamin D, prolonged immobilization, hyperthyroidism and treatment with certain medications.
Mild hypercalcemia does not always cause symptoms. At higher levels, symptoms may include:
- increased thirst and large amounts of urine
- fatigue and muscle weakness
- nausea or constipation
- depression or difficulty concentrating
- kidney stones
- confusion or impact on heart rhythm in severe hypercalcemia
An elevated value often needs to be checked with a new test and assessed together with, among other things, PTH, albumin, kidney function, phosphate and vitamin D.
What does a low calcium value mean?
A low calcium value is called hypocalcemia. This can occur, among other things, in cases of vitamin D deficiency, impaired kidney function, magnesium deficiency or low production of parathyroid hormone after illness or surgery in the area around the thyroid gland.
Symptoms of hypocalcemia can include:
- tingling or numbness around the mouth, in the hands or in the feet
- muscle cramps or muscle twitching
- increased nerve and muscle irritability
- fatigue or difficulty concentrating
- heart rhythm disturbances in severe hypocalcemia
A low total value does not always mean that the biologically active calcium is too low. A low albumin value can lower P-Calcium without affecting the ionized calcium.
Total calcium, albumin-corrected or ionized calcium
P-Calcium measures both free and bound calcium. Since some of the calcium is bound to albumin, a deviating albumin value can affect the result. In the case of low albumin, P-Calcium may appear low even though the amount of biologically active calcium is normal.
In some situations, the result may therefore need to be assessed together with P-Albumin or converted to albumin-corrected calcium. Analysis of ionized calcium may be more informative in cases such as clearly deviating albumin, kidney failure, serious illness or when the result does not match the symptoms.
How are the results interpreted?
The reference interval varies between laboratories and can also be affected by age. A common reference range for adults is approximately 2.15–2.50 mmol/L, but the range indicated on the current laboratory result should always be used.
A value outside the reference range is not a diagnosis in itself. The result needs to be assessed together with symptoms, medication, albumin and other relevant analyses. In case of deviating calcium values, supplementary tests such as PTH, vitamin D, albumin, phosphate, magnesium and creatinine may be relevant.
