Calcium (total)
What it measures, and what changes the number.
Total calcium measures all the calcium in the blood. Part of it is bound to proteins, mainly albumin, and part circulates in a free, or ionised, form that is the active portion.
Because so much calcium travels on albumin, it is usually read with albumin, and some labs also report an albumin-corrected calcium. It is also commonly ordered with PTH, phosphate, vitamin D and magnesium, which together regulate calcium in the body.
Collection can shift the number. Keeping the tourniquet on for a long time or strong fist clenching can raise total calcium, and posture has a small effect because it changes protein concentration. Samples collected in tubes containing EDTA or citrate cannot be used, since these bind calcium. Labs may print it as Calcio total.
Often read alongside: Albumin, PTH (intact), Phosphate, Vitamin D (25-OH), Magnesium