Medicine To diagnose GERD , in 24 hour ambulatory pH testing the percentage of the day that the pH was less than 4 is: A > 20% B > 1% C > 5 % D > 1 % 💡 Explanation To diagnose GERD , in 24 hour ambulatory pH testing the percentage of the day that the pH was less than 4 is: ✓ Correct Answer: C. > 5 %