Which ABG result is most consistent with metabolic acidosis?

• A. High pH and high HCO3
• B. High pH and low HCO3
• C. Normal pH with normal HCO3
• D. Low pH and low HCO3

Answer: (D)

Metabolic acidosis is defined by a decrease in bicarbonate (HCO3-) with a resulting drop in blood pH, reflecting an accumulation of acid or loss of base. The body tries to compensate by increasing ventilation to blow off CO2, so the pCO2 tends to fall as adjustment occurs.

The ABG result that shows both a lower pH and a lower HCO3- fits this pattern: acidemia with reduced bicarbonate, indicating metabolic acidosis. The other patterns do not reflect this primary metabolic disturbance: a high pH indicates alkalemia; a normal pH with normal HCO3- shows no acid-base disorder; a low pH with high HCO3- would imply a different or mixed disorder rather than metabolic acidosis.