American Board of Orthodontics (ABO) Practice Exam 2025 - Free Orthodontics Practice Questions and Study Guide.

The vitamin D metabolite that increases plasma phosphate levels is 1,25(OH)2D, also known as calcitriol. This metabolite is the active form of vitamin D and plays a crucial role in the regulation of calcium and phosphate metabolism in the body. Calcitriol stimulates the intestines to enhance the absorption of both calcium and phosphate from dietary sources. It also promotes renal tubular reabsorption of phosphate, which means it helps the kidneys retain more phosphate, thereby increasing the plasma levels of this mineral.

Additionally, calcitriol influences bone resorption, indirectly affecting serum phosphate levels by mobilizing phosphate from bone. Its primary functions center around maintaining mineral homeostasis, which is essential for various physiological functions, including bone integrity and overall metabolic processes.

The other options listed do not have the same metabolic impact on phosphate levels. While 25(OH)D is an important precursor that reflects vitamin D status in the body, it does not significantly affect phosphate metabolism directly. Vitamin D3 is the cholecalciferol form of vitamin D but is not active without conversion to its metabolites. Calcitriol is indeed another name for 1,25(OH)2D, but specifically identifying 1,25(OH)