This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
All are used in the diagnosis of diabetes mellitus except: 
Select and explain. 
A. FBS, B. HbAlc, C. D-xylose absorption test, D. OGTT
C: D-xylose absorption test
Answer: C: D-xylose absorption test 
Explanation: C i.e. D-xylose absorption testGlycosylated hemoglobin (HbAic, an index of average glucose level in preceding 12 weeks), Fasting blood sugar (FBS 126 mg/dl), oral glucose tolerance test (OGTT) i.e. 2 hour post prandial glucose levels (> 200 mg/dl) and random blood sugar (RBS > 200 mg(dl) are used to diagnose diabetes mellitus whereas D-xylose absorption test is used to determine absorption of D-xylose in proximal small intestine (duodenum & jejunum) to detect intestinal malabsorption syndrome.