Adjust your total calcium result for albumin level. Useful when serum albumin is low or high.
About 40% of calcium in the blood is bound to albumin (a protein). When albumin is low (e.g. in liver disease, kidney disease, malnutrition, inflammation), the total calcium can appear falsely low even though the physiologically active (ionised) calcium is normal.
The corrected calcium formula adjusts for this, giving a better estimate of what the total calcium would be if albumin were normal. It's particularly important when albumin is below 35 g/L or above 45 g/L.
If ionised calcium is available from a blood gas, it's a more accurate direct measurement and correction isn't needed.
High calcium (hypercalcaemia): Primary hyperparathyroidism (most common outpatient cause), malignancy, excess vitamin D, thiazide diuretics, sarcoidosis, prolonged immobilisation.
Low calcium (hypocalcaemia): Vitamin D deficiency (most common cause in Australia), chronic kidney disease, hypoparathyroidism (e.g. after thyroid surgery), magnesium deficiency, pancreatitis.
Symptoms of high calcium include nausea, thirst, constipation, confusion, and bone pain. Low calcium can cause muscle cramps, tingling, and in severe cases, cardiac arrhythmias.
Total calcium in blood is partly bound to albumin. When albumin is low (liver disease, nephrotic syndrome, malnutrition, critical illness), total calcium appears falsely low even though the active (ionised) calcium may be normal. Correcting for albumin gives a better estimate of true calcium status.
Note: If ionised calcium is available, it is more accurate than corrected calcium and does not require albumin correction. Ionised calcium is often available on blood gas samples.