hypercalcemia
Meaning of hypercalcemia: Calcium is held in a narrow range, and pushing it above that range makes nerves and muscles sluggish rather than excitable.
Definition of hypercalcemia
Hypercalcemia is a calcium level in the blood above the normal range. Most calcium sits locked in bone and only a small fraction circulates, so the blood level is held steady by hormones that shift calcium between bone, gut and kidney. When that control fails the level rises, slowing nerve and muscle signaling, dulling the gut and driving fluid loss through the kidney.
What pushes the level up?
Two causes account for most cases, and they turn up in quite different settings. An overactive parathyroid gland releases too much of the hormone that pulls calcium out of bone and holds it back in the kidney. That is the usual explanation when a raised level is found by chance in someone who feels well. Cancer is the usual explanation in someone already unwell in hospital, and there the level tends to climb faster and further.
| Cause | How it raises calcium |
|---|---|
| Overactive parathyroid gland | Excess parathyroid hormone strips calcium from bone |
| Cancer | A tumor protein imitates that hormone, or deposits in bone dissolve it |
| Too much vitamin D | More calcium is absorbed from food |
| Granulomatous disease | Clumps of immune tissue make active vitamin D of their own |
| Certain medicines | Thiazide diuretics and lithium shift the balance upward |
How does it show itself?
Calcium quiets excitable tissue, so the effects read as a general slowing down. Thirst and heavy urine output come first, because the kidney loses its grip on water when calcium is high, and the dehydration that follows pushes the level higher still. The gut slows, giving constipation, nausea and loss of appetite. Muscles feel weak. Higher levels blunt concentration, then bring confusion and drowsiness. Long-standing mild elevation behaves differently again, working quietly on the skeleton and the kidney and surfacing as thinning bone or stones rather than as anything noticed day to day. A rapid rise causes far more trouble than a slow one at the same number, because nothing has had time to adjust.
Why can the measurement mislead?
Much of the calcium in blood travels stuck to albumin, a carrier protein, and only the free portion is active. A standard test reports the two added together. Someone whose albumin is low, which is common in serious illness, therefore has a total figure that understates the free fraction, and a genuine excess can hide behind a normal-looking result. The number is either adjusted for albumin or the free fraction is measured directly.
Also known as
Used in a sentence
Laboratory testing on admission showed hypercalcemia attributed to widespread bone metastases.
Good to know
Much of the calcium in blood is bound to albumin and only the free fraction is active, so a low albumin level lowers the measured total and can conceal a genuine excess unless the result is corrected or the free fraction measured.
Word origin
Where “hypercalcemia” comes from
Hyper- is Greek for above or beyond, and the ending -emia comes from the Greek haima, meaning blood, so the word reads as calcium above normal in the blood.