Calcium blood test: what high or low calcium means

Total calcium and ionized calcium

• Total calcium is the standard test on a CMP. It counts calcium bound to proteins plus free calcium.
• Ionized calcium is only the free, active form. It is harder to run, so it is ordered when total calcium is off, when albumin is abnormal, or during serious illness or surgery.

Your body keeps calcium in a tight range using parathyroid hormone (PTH) and vitamin D. Too much of either can raise it, and too little can lower it.

Why albumin matters

Total calcium moves about 0.8 mg/dL for every 1 g/dL change in albumin, in the same direction. So if albumin is low, total calcium reads low even when the active calcium is normal.

Clinicians often adjust (correct) total calcium for albumin, or order an ionized calcium test, before deciding whether calcium is truly low or high. Low albumin can also hide a truly high ionized calcium.

What a high calcium can mean

Hypercalcemia is a total calcium above about 10.4 mg/dL. Common causes:

• Primary hyperparathyroidism, an overactive parathyroid gland. The most common cause outside the hospital.
• Cancer, including cancer that has spread to bone. More common in hospitalized patients.
• Too much vitamin D, usually from high-dose supplements.
• Medicines, such as thiazide diuretics and lithium.
• Other causes: sarcoidosis and other granulomatous diseases, long bed rest, and large amounts of calcium antacids (milk-alkali syndrome).

Many people have no symptoms. When present they can include thirst, frequent urination, constipation, nausea, kidney stones, bone or muscle aches, fatigue and confusion.

What a low calcium can mean

• Low albumin, from liver disease or malnutrition. Check this first.
• Low vitamin D or low magnesium. See vitamin D.
• Underactive parathyroid glands (hypoparathyroidism), including after neck surgery.
• Kidney disease and pancreatitis.
• Some medicines, such as phenytoin, phenobarbital and rifampin.

Symptoms can include muscle cramps, tingling around the lips or in the fingers and feet, and, when very low, spasms or seizures.

What to do with an abnormal result

1. Look at albumin on the same report and ask whether the calcium needs correcting or an ionized calcium test.
2. Ask about PTH and vitamin D. A high or high-normal calcium with a PTH that isn't low suggests the parathyroid glands, and needs a workup rather than supplements.
3. List supplements and medicines, especially vitamin D, calcium, antacids, thiazides and lithium. You may be asked to pause some before a retest; don't stop any medicine on your own.
4. Retest to confirm. One mildly abnormal value is often repeated.

Get urgent care if abnormal calcium comes with confusion, extreme thirst and urination, severe belly pain or vomiting, muscle spasms, tingling around the mouth, an irregular heartbeat or a seizure. Calcium above about 12 mg/dL or below about 7 mg/dL can cause serious symptoms.