Renal clearance greater than GFR
Inulin is freely filtered and neither reabsorbed nor secreted, so its clearance equals GFR. A drug's clearance is twice that of inulin. What can be concluded?
Answer A: explanation for every choice
A
Correct. Clearing more plasma than is filtered requires the tubules to add the drug to the urine.
B
Net reabsorption makes clearance lower than GFR.
C
An unfiltered substance could only be cleared by secretion. Clearance above GFR doesn't tell us it isn't filtered.
D
Protein binding reduces filtration, which would lower clearance.
TakeawayClearance > GFR → net secretion. Clearance < GFR → net reabsorption.
Equation usedRenal clearance
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