Adjusted calcium (also called corrected calcium) is a calculated value that accounts for the effect of albumin on total calcium measurements. Approximately 40–45% of calcium in the blood is bound to albumin, a proportion that varies significantly. When albumin is low — as commonly occurs in illness, malnutrition, or liver disease — total calcium appears artificially low even when the physiologically active ionised calcium is normal. The adjustment formula corrects for this, providing a more reliable estimate of true calcium status.

Calcium is essential for bone structure, muscle contraction, nerve signalling, cardiac function, and blood clotting. The body maintains blood calcium within a very tight range through the interplay of parathyroid hormone (PTH), active vitamin D, and calcitonin. Abnormal adjusted calcium — whether high (hypercalcaemia) or low (hypocalcaemia) — can have serious clinical consequences and is always investigated further to identify the underlying cause.