Final answer:
Stool samples with elevated reducing substances and decreased pH can diagnose lactose intolerance, a condition where insufficient lactase production in the small intestine leads to undigested lactose causing symptoms such as gas and diarrhea. Option A is correct.
Step-by-step explanation:
Stool samples with elevated reducing substances and decreased pH are indicators typically associated with lactose intolerance. In lactose intolerance, the small intestine does not produce enough lactase, the enzyme necessary for digesting lactose, the milk sugar. Undigested lactose in the large intestine is fermented by bacteria, resulting in gas, cramps, bloating, diarrhea, and acidic stools. This condition is notably different from celiac disease, irritable bowel syndrome, and inflammatory bowel disease, which involve other pathologies and do not typically present with elevated reducing substances in stool.
Although intestinal biopsy and tests like the hydrogen breath test can also be used in the diagnosis of lactose intolerance, they are more complicated and less routinely done compared to the stool acidity test. Symptom severity in lactose intolerance can range from mild discomfort to severe pain, but notably, the symptoms are resolved once the lactose is eliminated.