Hypercalcemia (high calcium)

Hypercalcemia is a raised level of calcium in the blood. Calcium is controlled mainly by parathyroid hormone (PTH) from the parathyroid glands and by vitamin D, which together balance calcium in the bones, gut and kidneys. When this control goes wrong, or calcium is released from bone, the blood level rises. By far the two commonest causes are: an overactive parathyroid gland (primary hyperparathyroidism), usually from a small benign growth on the gland, which is the leading cause in otherwise well people found on a routine test; and cancer, which can raise calcium by spreading to bone or by producing a PTH-like substance, and is the commonest cause in people who are unwell. Measuring PTH is the key step that separates these — it is high or inappropriately normal in hyperparathyroidism, and suppressed (low) when a cancer is driving the calcium up. Other causes include too much vitamin D or calcium, certain medications, prolonged immobility, and some other conditions. Because much of the blood's calcium is carried on the protein albumin, the level is 'corrected' for albumin so it is read accurately. Symptoms — sometimes summarised as 'bones, stones, groans and moans' — reflect effects on bones, kidneys (stones and excessive urination), the gut (constipation) and the brain (tiredness, low mood, confusion).

• Calcium (corrected for albumin) — the defining test; albumin is needed to interpret it accurately.
• Parathyroid hormone (PTH) — the key next step: high/normal points to hyperparathyroidism; low/suppressed points to a cancer or other cause.
• Phosphate — often low in hyperparathyroidism.
• Vitamin D — to check for excess or deficiency.
• Kidney function — high calcium can affect the kidneys.

• Often no symptoms when mild
• Excessive thirst and frequent urination
• Constipation and abdominal discomfort
• Nausea and loss of appetite
• Tiredness, weakness and low mood
• Confusion (in more severe cases)
• Bone pain, and kidney stones over time