L3: Measuring GFR and Renal Clearance

Question 1

Equation for filtered load

Answer 1

FLx = (GFR)(Px)

Question 2

Equation for excretion rate (2)

Answer 2

ERx = FLx + Sx - Rx
ERx = (Ux)(V)

Question 3

If Rx and Sx = 0, then

Answer 3

ERx = FLx

Question 4

Equation for GFR (using urine concentration)

Answer 4

GFR = (Ux)(V)/Px

Question 5

Describe the perfect GFR marker. What 2 substances can be used for this.

Answer 5

Freely filtered, but neither absorbed or secreted

• Inulin (more accurate)
• Creatinine (used more in clinical setting; secreted slightly)

Question 6

How can you measure GFR using Cr clearance?

Answer 6

Ccr= (UCr)(V)/PCr ~ GFR

Question 7

If Cx > GFR, then substance was

Answer 7

Secreted

Question 8

If Cx < GFR, then substance was

Answer 8

Absorbed

Question 9

What is the clearance ratio?

Answer 9

Cx/Cinulin

Question 10

If Cx/Cinulin is = 1.0, then

Answer 10

substance if GFR marker (inulin has perfect clearance)

Question 11

If Cx/Cinulin < = 1.0, then

Answer 11

substance was either not filtered, or was filtered and absorbed

Question 12

If Cx/Cinulin is > 1.0, then

Answer 12

substance was filtered and secreted

Question 13

CPAH is an estimate of what?

Answer 13

RPF (since all blood is cleared of PAH)