WHAT HAPPENED
You selected Reduced proximal bicarbonate reabsorption. Your response
history also included a change toward the correct option, which suggests meaningful partial
knowledge even though the final answer was incorrect.
KEY DISCRIMINATOR
Prioritize Urine pH is 6.3 and recurrent nephrolithiasis. Together, these findings distinguish Alkaline Urine in Type 1 RTA from the subtype represented by Reduced Bicarbonate Threshold in Type 2 RTA.
WHAT TO DISTINGUISH
The best explanation is Defective distal hydrogen secretion in the Collecting duct. The selected answer instead matched the
competing subtype pattern. This was a narrow subtype-discrimination error rather than
evidence of a broad gap.
Review how Urine pH is 6.3 functions as a discriminator for Alkaline Urine in Type 1 RTA, then practice using it to
separate this pattern from Reduced Bicarbonate Threshold in Type 2 RTA.