Identify one electrolyte abnormality commonly seen in CKD and one bone metabolism abnormality often associated with it.

• A. Hyperkalemia; secondary hyperparathyroidism with hypocalcemia due to phosphate retention.
• B. Hypokalemia; secondary hyperparathyroidism with hypocalcemia due to phosphate retention.
• C. Metabolic acidosis; osteopenia due to vitamin D deficiency only.
• D. Hyponatremia; renal osteodystrophy with hypercalcemia.

Answer: (C)

In CKD, two types of disturbances are especially common: electrolyte/acid-base imbalance and bone-mineral metabolism problems. The kidneys’ reduced ability to excrete acids leads to metabolic acidosis, with decreased bicarbonate and hydrogen ion retention. This acidosis also affects bones, as bone minerals are mobilized to buffer the acid, contributing to bone loss over time.

For bone metabolism, phosphate retention is a hallmark consequence of kidney dysfunction. As phosphate builds up, calcium levels fall, which stimulates the parathyroid glands to release more PTH. This secondary hyperparathyroidism drives bone resorption in an effort to normalize calcium, leading to renal osteodystrophy—changes in bone turnover and strength.

Therefore, pairing metabolic acidosis with secondary hyperparathyroidism with hypocalcemia due to phosphate retention best captures the common electrolyte disturbance and the characteristic bone-mineral disorder seen in CKD.

While vitamin D deficiency can contribute to bone issues, CKD-related bone disease is not limited to osteopenia from vitamin D deficiency alone; it involves complex interactions of phosphate, calcium, PTH, and altered vitamin D metabolism, making secondary hyperparathyroidism the more representative bone abnormality in this context.