Which carbohydrate is a homoglycan of fructose formerly used to determine GFR?

• A. Inulin
• B. Cellulose
• C. Dextran
• D. Chitin

Answer: (A)

The key idea is using a marker that is freely filtered by the kidneys and neither reabsorbed, secreted, nor metabolized—so its clearance equals the glomerular filtration rate. Inulin fits perfectly: it is a polymer of fructose (a fructan), making it a homoglycan of fructose. Because the kidneys filter it but do not reabsorb or secrete it, its plasma clearance directly reflects GFR. Historically, this made inulin the gold standard for measuring GFR.

The other substances are not appropriate markers here. They are polymers of other sugars (for example, cellulose is a glucose polymer, chitin is N-acetylglucosamine, dextran is a glucose polymer with varying structures), and they do not share inulin’s ideal filtration properties, so they don’t provide an accurate measurement of GFR.