In chronic renal failure, which disturbance is most likely?

• A. Decreased serum phosphate level secondary to kidney failure.
• B. An increased serum calcium level secondary to kidney failure.
• C. Metabolic alkalosis secondary to retention of hydrogen ions.
• D. Water and sodium retention secondary to a severe decrease in the glomerular filtration rate.

Answer: (D)

When kidney function falls, the ability to excrete water and sodium is impaired. A severe drop in glomerular filtration rate leads to fluid and sodium retention, causing volume overload, edema, and hypertension. This makes water and sodium retention the most likely disturbance in chronic renal failure.

Phosphate handling also changes, but not as a decreased phosphate level—rather, phosphate tends to accumulate (hyperphosphatemia), which can lower calcium levels and promote secondary hyperparathyroidism, not an increased calcium level. The problem with hydrogen ion handling is opposite too: failing kidneys cause metabolic acidosis, not metabolic alkalosis, due to reduced acid excretion.