Corrected calcium test: normal range and what the result means

Most of the body's calcium is stored in the bones, and the rest circulates in the blood - part of it in the free (ionised) form, part of it bound to the protein albumin. Because the total calcium test measures both of these parts together, when the amount of albumin in the blood is decreased or increased the total calcium result can misleadingly look low or high even though the amount of free calcium is in fact normal. That is why the calcium value is mathematically corrected for the albumin concentration - the result is corrected calcium, which better reflects the real calcium metabolism in the body.

Corrected calcium is most often calculated automatically in the laboratory, or the doctor calculates it when total calcium and albumin are both known. Calcium in the body matters for the strength of the bones and teeth, for muscle contraction, for the transmission of nerve impulses and for blood clotting, and its amount is regulated by parathyroid hormone and vitamin D.

• When total calcium or albumin in the blood deviates from its normal range and the doctor needs a more precise assessment of calcium metabolism
• When bone disease is suspected, or when changes in bone density are being investigated
• When a parathyroid gland disorder is suspected (hyperparathyroidism or hypoparathyroidism)
• In kidney or liver disease, which change albumin and calcium metabolism
• During a long period spent in bed or long-term immobility
• When investigating certain cancers or absorption disorders of the digestive tract

A raised corrected calcium is considered high against the 2.58 mmol/l limit given by MedlinePlus. The most common causes are a parathyroid gland disorder (hyperparathyroidism), cancers, long-term immobility, or taking too much calcium and vitamin D. Always discuss the result with your doctor, together with other tests.

Causes of high corrected calcium

• Hyperparathyroidism - overactive parathyroid glands
• A long period of bed rest or immobility
• Taking too much calcium or vitamin D
• Some cancers, including multiple myeloma
• Inflammatory conditions that cause granulomas (for example sarcoidosis)
• An overactive thyroid, or too large an amount of thyroid hormone preparations
• Paget's disease
• Some medicines - certain diuretics and medicines prescribed for mood disorders

What to discuss with a doctor

• A parathyroid hormone (PTH) test - it helps to tell a parathyroid gland cause apart from the others
• The amount of vitamin D in the blood
• Kidney and thyroid function markers
• A review of the supplements and medicines being taken, together with your doctor
• When to repeat the test, so that a change over time can be seen

Low corrected calcium

A lowered corrected calcium is considered low against the 2.20 mmol/l limit given by MedlinePlus. The most common causes are underactive parathyroid glands, kidney failure, a deficiency of vitamin D or magnesium, and absorption disorders of the digestive tract. Discuss the result with your doctor, together with other tests.

• Hypoparathyroidism - underactive parathyroid glands
• Kidney failure or another kidney disease
• Vitamin D deficiency
• Magnesium deficiency
• Absorption disorders of the digestive tract
• Liver disease
• Inflammation of the pancreas (pancreatitis)

What to discuss with a doctor when it is low

• Parathyroid hormone (PTH) and vitamin D tests
• Magnesium and kidney function markers
• An examination of the digestive system, if an absorption disorder is suspected
• When to repeat the test, so that a change over time can be seen

Corrected calcium and ionised calcium

Ionised calcium measures only the free form of calcium directly and is considered the most accurate, but it requires special handling of the sample. Corrected calcium is used more often as a more practical alternative, when only total calcium and albumin results are available. Total calcium measures all of the calcium in the blood - both the free part and the part bound to albumin; corrected calcium is that same value recalculated according to the amount of albumin, so it shows the real calcium metabolism more accurately when albumin is decreased or increased.

Reading the result

A deviation can be linked with the condition of the parathyroid glands, the kidneys, the liver or the bones, with the amount of vitamin D or magnesium, and with other causes. The exact cause is determined by a doctor, who assesses the result together with other tests and symptoms. More on results in general: how to read blood test results. Related tests: total calcium, ionised calcium, parathyroid hormone, phosphorus, vitamin D and magnesium.