What condition leads to decreased total calcium levels?

The condition that leads to decreased total calcium levels is chronic kidney disease. In chronic kidney disease (CKD), the kidneys become less effective at filtering waste and regulating various body functions, including mineral metabolism. One of the key issues in CKD is the disruption of calcium and phosphate balance. As kidney function declines, the ability to excrete phosphate diminishes, leading to hyperphosphatemia. Elevated phosphate levels can bind to calcium and lead to decreased bioavailability of calcium. Additionally, as kidney function worsens, there is often a decrease in the activation of vitamin D, which is crucial for calcium absorption in the intestines. This combination results in lower total calcium levels in the bloodstream.

In contrast, dehydration can concentrate calcium levels due to reduced plasma volume, sepsis typically results in normal or elevated calcium levels due to increased mobilization from bones, and excessive vitamin D generally raises serum calcium levels due to increased intestinal absorption.