Hi Mayblin,

Sure. A little background first. The form of calcium in your body that is considered physiologically active is called calcium ion or free calcium (Ca2+). When you read the "calcium" on your blood test, it's total calcium. Total calcium is roughly 45% calcium ion, 45% calcium bound to albumin, and 10% other calcium compounds (like calcium phosphate, calcium sulfate...).

Since measuring calcium ion is a bit tricky and more expensive, most doctors just use total calcium and assume the percentages listed above. When you use total calcium, you should adjust the number based on the blood albumin when albumin is less than 4. The equation for the adjustment is: Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]). If you like, here is a link to a calculator https://perinatology.com/calculators/Corrected%20Calcium.htm .

I'm putting together a presentation on Calcium and Vitamin D for Osteoporosis now. Below is the draft slide on corrected calcium.