In which condition would serum phosphate likely be low along with elevated parathyroid hormone levels?

In the context of vitamin D deficiency, the serum phosphate levels are likely to be low due to the impaired intestinal absorption of phosphate. Vitamin D plays a crucial role in facilitating the absorption of calcium and phosphate from the gastrointestinal tract. When vitamin D is deficient, there is a resultant decrease in the absorption of these minerals, leading to low serum phosphate levels.

In response to decreased serum calcium levels, which can also occur due to low vitamin D, the parathyroid glands release elevated levels of parathyroid hormone (PTH). PTH works to increase calcium levels by releasing calcium from bones, increasing renal tubular reabsorption of calcium, and indirectly promoting increased intestinal absorption of calcium through the activation of vitamin D. However, in vitamin D deficiency, despite these compensatory mechanisms, serum phosphate levels remain low.

This combination of low phosphate and elevated parathyroid hormone is a classic metabolic disturbance seen in vitamin D deficiency, distinguishing it from other conditions related to parathyroid hormone dynamics.