Clearance And Kidney Function

Question 1

What is clearance?

Answer 1

Volume of plasma cleared of a substance in unit time

Question 2

Why do we use clearance as a marker of kidney function?

Answer 2

We cannot actually measure GFR, only infer it

Question 3

Why does inulin provide a perfect model for GFR?

Answer 3

It is filtered fully, not reabsorbed and not secreted

It can be introduced to the body at a steady rate

Question 4

What happens to GFR in pregnancy?

Answer 4

Increases by approximately 50%

130-180ml/min

Question 5

Why do we often not use inulin to measure GFR?

Answer 5

Requires a continuous IV - costly

Requires catheter and time urine collection - unrealistic

Question 6

What other markers do we use to infer GFR?

Answer 6

51 CR EDTA (in children or for kidney transplant assessment)

Creatinine

Question 7

What factors affect creatinine levels and therefore inference of GFR?

Answer 7

Meat intake
Muscle mass
Excercise frequency
Certain drugs eg trimethoprim

Question 8

What is eGFR?

Which type is used in UHL?

Answer 8

Best guess of GFR using serum creatinine

MDRD eGFR

Question 9

What are the limitations of the MDRD eGFR

Answer 9

Inaccurate in people without kidney disease, children, elderly, pregnant, amputees and those of differing ethnicities

Question 10

Who does the MDRD eGFR work best for?

Answer 10

Caucasian or black ethnicities

Standardised for age, sex, diabetes