Which value is used to assess the kidneys’ role in acid-base balance (renal buffering)?

• A. pH
• B. PaO2
• C. Bicarbonate (HCO3-)
• D. SpO2

Answer: (C)

The kidneys influence acid-base balance by managing bicarbonate, so the value that reflects the renal buffering capacity is bicarbonate (HCO3-). Bicarbonate acts as the main extracellular buffer, and the kidneys maintain it by reabsorbing filtered HCO3- and producing new HCO3- to neutralize excess hydrogen ions. In metabolic acidosis, HCO3- drops because buffering capacity is overwhelmed; renal compensation aims to raise HCO3- by reabsorbing more and generating new bicarbonate. In metabolic alkalosis, HCO3- rises. pH shows the overall acid-base status but is influenced by both lungs and kidneys, whereas PaO2 and SpO2 relate to oxygenation, not buffering. So HCO3- is the best indicator of renal buffering.