**Core Concept**
Thiazide diuretics are a class of medications used to treat hypertension and edema. They work by inhibiting the sodium-chloride cotransporter in the distal convoluted tubule of the kidneys, leading to increased sodium and water excretion.

**Why the Correct Answer is Right**
Thiazides cause a decrease in calcium reabsorption in the kidneys, which results in increased calcium excretion. This is due to the inhibition of the sodium-chloride cotransporter, which is also involved in calcium reabsorption. As a result, thiazides can lead to hypocalcemia, especially in patients with normal or low calcium levels. The increased excretion of calcium can also lead to a decrease in parathyroid hormone (PTH) secretion, as the body attempts to conserve calcium.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as thiazides do not cause an increase in potassium levels. In fact, they can lead to hypokalemia due to increased potassium excretion.
**Option B:** This option is incorrect as thiazides do not cause an increase in blood glucose levels. They can actually have a beneficial effect on blood sugar control in patients with type 2 diabetes.
**Option C:** This option is incorrect as thiazides do not cause an increase in uric acid levels. In fact, they can lead to a decrease in uric acid levels due to increased excretion.

**Clinical Pearl / High-Yield Fact**
Thiazides are often used in combination with other medications, such as ACE inhibitors or beta-blockers, to treat hypertension. It is also essential to monitor patients on thiazide diuretics for hypokalemia, hypomagnesemia, and hypocalcemia.

**Correct Answer:** D. Decreased calcium levels