Exam 3: Lecture 31

Question 1

Why do we measure GFR?

Answer 1

To measure renal function

Question 2

A substance used to measure GFR has to meet what 4 criteria?

Answer 2

1. freely filtered
2. cannot be reabsorbed or secreted by renal tubule
3. cant alter GFR
4. must be excreted only by the kidney, not metabolized

Question 3

What is the ideal marker for GFR?

Answer 3

Inulin

Question 4

T/F: the amount of inulin filtered is slightly more than the amount of inulin excreted.

Answer 4

False - inulin filtered = inulin excreted

Question 5

If the clearance of inulin is decreased, then what happens to GFR?

Answer 5

Decreases; clearance of inulin = GFR

Question 6

What is the filtration fraction?

Answer 6

The fraction of RPF filtered across glomerular capillaries.

Question 7

How is the filtration fraction altered/regulated?

Answer 7

Altering arteriole resistance

Question 8

What is the normal range of filtration fraction for domestic animals?

Answer 8

10-40%

Question 9

What are the other 4 GFR markers that we can use?

Answer 9

• Creatinine
• BUN
• SDMA
• Phosphorous

Question 10

Which GFR marker is heavily influenced by the loss of muscle mass?

Answer 10

Serum creatinine

Question 11

If using serum creatinine, how much of the nephrons must lose function before there will be a clear sign on the blood work?

Answer 11

over 75% functionality must be lost

Question 12

In a 18y/o cat, BCS of 3/9, with chronic kidney disease, which GFR marker would NOT be ideal to use?

Answer 12

Serum creatinine

Question 13

Which GFR marker is synthesized in the liver and is the end-product of protein catabolism?

Answer 13

BUN

Question 14

What is a negative aspect of using BUN as a GFR marker?

Answer 14

It is not produced at a constant rate

Question 15

The amount of BUN can vary on what two factors?

Answer 15

• Dietary protein intake
• Measuring during fasting or postprandial

Question 16

In a patient with renal failure, what would you expect to happen to the BUN:CREA ratio?

Answer 16

No change - both substances increase together

Question 17

In a dehydrated patient, what would you expect to happen to the BUN:CREA ratio?

Answer 17

Increase - urea is reabsorbed

Question 18

In a hypovolemic patient, what would you expect to happen to the BUN:CREA ratio?

Answer 18

Increase - increase urea reabsorption

Question 19

When testing a patient for CKD, which value would you expect to see an increase in first: SDMA or CREA?

Answer 19

SDMA

Question 20

T/F: SDMA is not affected by muscle mass.

Answer 20

True

Question 21

You run an SDMA test on a suspected CKD patient. It’s levels are increased slightly, is this enough to diagnose this patient with CKD?

Answer 21

No, it is suggestive, but the increase in SDMA should be persistent over 2-3 months.

Question 22

As GFR decreases, what happens to serum phosphorus concentrations?

Answer 22

Increases (hyperphosphatemia)

Question 23

When evaluating a patient’s kidney function, which marker is the best to use for a diagnosis?

Answer 23

All of them! Use multiple markers to work towards a diagnosis.