This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
Which is not a test for diabetes mellitus - 
Select and explain. 
A. Fasting blood sampling, B. Random blood sampling, C. D-xylose, D. Oral glucose tolerance test
C: D-xylose
Answer: C: D-xylose 
Explanation: D-xylose absorption is a laboratory test to determine how well the intestines absorb a simple sugar (D-xylose). The test helps determine if nutrients are being properly absorbed. It is done in : persistent diarrhea, signs of malnutrition, unexplained weight loss. Rest of the options are the tests done in diabetes mellitus. Ref - Harrisons internal medicine 20e topic diabetes