In metabolic acidosis due to renal failure, which statement best describes the abnormality?

• A. The pH decreases
• B. Bicarbonate decreases
• C. Hydrogen ion concentration increases
• D. The anion gap increases

Answer: (C)

In renal failure, the key problem is the kidney’s inability to excrete hydrogen ions. As these hydrogen ions accumulate in the blood, their concentration rises, which drives the pH down and creates acidemia. Bicarbonate buffering is overwhelmed, so bicarbonate tends to fall as it neutralizes the excess hydrogen ions. The result is metabolic acidosis with a rise in hydrogen ion concentration as the most direct descriptor of the abnormality. The actual pH drop and the bicarbonate decline follow from that excess of H+, while the anion gap can vary depending on the accompanying acids.