The serum calcium test can be used to monitor a patient’s response to treatment with calcium channel blockers such as amlodipine, diltiazem, felodipine, nifedipine, and verapamil. These drugs work by inhibiting the flow of calcium into the cells, promoting arterial relaxation and decreasing peripheral vascular resistance.About half of the body’s calcium is found in its ionized or free form, while the other half is bound to albumin. Calcium
testing results in two measurements: the serum calcium level, which is a total of both forms of calcium, and the ionized calcium level.
Normally, blood levels of total calcium range from 9.0 to 10.5 mg/dl, and blood levels of ionized calcium range from 4.4 to 5.0 mg/dl.
Certain factors can affect the results of calcium testing. Thiazide diuretics can cause hypercalcemia. Also, prolonged use of a tourniquet when performing the venipuncture can increase the calcium level by decreasing blood pH.