Calcium (serum or urine)

The test measures total serum calcium and, when needed, urine calcium. Blood calcium reflects the balance between parathyroid hormone, vitamin D, kidneys and bones. It is used for symptoms suggesting high or low calcium, kidney, parathyroid and bone disease, and with medicines that alter calcium levels.

Who the test is for

• people with increased thirst and frequent urination, nausea, constipation, fatigue or kidney stones;
• people with tingling around the mouth and fingers or muscle cramps in the hands and feet;
• people with kidney and parathyroid disease and after thyroid surgery;
• people with osteoporosis to rule out other causes, and before certain osteoporosis medicines;
• people taking higher vitamin D doses, thiazide diuretics or lithium long term;
• adults having a general check-up.

What calcium is and what the test indicates

Approximately 99 % of body calcium is in bones and teeth. The small remaining amount in blood and tissues is needed for muscle and nerve function, heart rhythm and blood clotting. The body keeps blood calcium within a narrow range with the help of parathyroid hormone (PTH), the active form of vitamin D and the kidneys. When calcium falls, PTH rises: it releases calcium from bone, reduces calcium loss in urine and stimulates active vitamin D production, increasing calcium absorption from food.

Blood calcium therefore does not show how much calcium is in bones or how much you consume. Blood calcium is usually normal in osteoporosis, and bone density is measured by densitometry.

Approximately half of blood calcium is bound to proteins, mainly albumin, while most of the rest is free, active ionised calcium. When albumin is low, total calcium can be low even if enough active calcium is present.

A doctor requests urine calcium for recurrent kidney stones, investigation of high blood calcium and monitoring certain treatments.

Panels including this test

Test Calcium (serum) is also included in this panel.

Energy balance panelvitamin D, vitamin B12, folic acid, calcium, magnesium and 498.50€Details ›

All panels including Calcium (serum) (8) ›

Preparation and sample

Venous blood is used for the blood test. Fasting is not required unless other tests that day need it. At sampling, state which medicines and supplements you take, particularly calcium, vitamin D, diuretics or lithium, but do not stop them without medical agreement.

Urine calcium most often requires urine collected over 24 hours.

How results are interpreted

Calcium is expressed in mmol/L. In adults, total serum calcium is usually approximately 2,14 to 2,53 mmol/L, with exact limits depending on age, laboratory and method and printed on your report. A doctor interprets results alongside albumin, PTH, vitamin D, creatinine, phosphorus and magnesium. When albumin is outside the range, a doctor may calculate corrected calcium or request ionised calcium.

High calcium (hypercalcaemia)

In people who otherwise feel well, the most common cause is primary hyperparathyroidism, overactivity of one or more parathyroid glands, often discovered incidentally. Calcium also rises in some malignancies, usually already known and advanced, excessive vitamin D intake, with thiazide diuretics and lithium, prolonged immobility and rarer conditions such as sarcoidosis. If PTH is also high or high-normal alongside elevated calcium, the parathyroid glands are the most likely cause; if PTH is low, another cause is sought.

Mild hypercalcaemia often causes no symptoms. More pronounced elevation causes thirst and frequent urination, nausea, loss of appetite, constipation, fatigue and kidney stones. Vomiting, confusion and drowsiness with high calcium require emergency care.

Low calcium (hypocalcaemia)

Low total calcium is often simply due to low albumin. Truly low calcium occurs in vitamin D deficiency, chronic kidney disease, low magnesium and after neck surgery if parathyroid glands are damaged. In vitamin D deficiency and kidney disease, PTH is usually elevated, while in underactive parathyroid glands it is low.

Tingling around the mouth and fingers and muscle cramps occur. Whole-body spasms, breathing difficulty or an irregular heartbeat require emergency care.

Urine calcium

Urine calcium depends on diet and is interpreted alongside blood calcium. Increased calcium excretion is a common risk factor for kidney stones. Low urine calcium with high blood calcium may suggest familial hypocalciuric hypercalcaemia, a rare inherited condition that usually needs no treatment.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Every branch accepts urine samples for calcium. Prices for all tests and panels are available in the service price list. Calcium is also measured in the Energy Balance Panel, alongside vitamin D, magnesium and electrolytes.

Frequently asked questions

Does blood calcium show whether I have osteoporosis?

No. Blood calcium is usually normal in osteoporosis because the body maintains it even at the expense of bones. Osteoporosis is confirmed by densitometry, while calcium, vitamin D and PTH are checked to exclude other causes of bone loss.

Can vitamin D and calcium supplements raise blood calcium?

Rarely at usual doses. Long-term high-dose vitamin D without medical supervision can raise calcium and burden the kidneys. Read more in the article on vitamin D replacement.

What is corrected calcium?

It is a calculated value that adjusts total calcium for albumin to estimate whether active calcium is adequate when albumin is low or high. The estimate is approximate, so a doctor requests ionised calcium in unclear cases.