Lecture 4-Measurement of Kidney Function

Question 1

What is GFR?

Answer 1

Glomerular filtration rate = amount of filtrate produced from blood flow per unit time

Question 2

What is the normal range for GFR?

Answer 2

90-120 ml/min/1.73m^2

Question 3

What does GFR depend on?

Answer 3

Gender, age, size of individual and kidneys, pregnancy

Question 4

When does nephron development finish?

Answer 4

35th-36th week of development

Question 5

After what age does GFR start to decline?

Answer 5

30 y/o

Question 6

What can compensatory hypertrophy of nephrons lead to?

Answer 6

Cortical scars and atrophy due to poor blood supply

Question 7

What is clearance?

Answer 7

Volume of plasma cleared of substance per unit time

Question 8

What is the equation for clearance?

Answer 8

C = A (amount of substance eliminated from plasma) / P (plasma conc of substrate)

Question 9

What is renal clearance?

Answer 9

[U (amount of urine) x V (urine flow rate)] / P

Question 10

If used to measure kidney clearance, a substance should have what properties?

Answer 10

• be produced at a constant rate
• be freely filtered
• not be reabsorbed
• not be secreted

Question 11

What is the best GFR marker?

Answer 11

Inulin

Question 12

Why is inulin not used to measure GFR?

Answer 12

It requires constant IV and needs a catheter and timed urine collections

Question 13

Which radioactively labelled marker can be used to measure GFR?

Answer 13

51 Cr-EDTA

Question 14

True or false: 51 Cr-EDTA has a 20% lower clearance than inulin

Answer 14

FALSE - 10%

Question 15

Which is the most commonly used marker for GFR?

Answer 15

Creatinine

Question 16

What is creatinine?

Answer 16

End product of muscle breakdown

Question 17

Is creatinine clearance an overestimate or underestimate of GFR?

Answer 17

Overestimate by 10-20% because it is secreted into the nephron

Question 18

What affects creatinine levels?

Answer 18

• intake
• metabolism
• bowel excretion
• renal excretion and secretion

Question 19

What can increase serum creatinine?

Answer 19

• large muscle bulk
• black male
• supplements, lots of meat
• drugs (trimethoprim)

Question 20

What can decrease serum creatinine?

Answer 20

• reduced muscle mass
• old, hispanic/Indo-Asian female
• vegetarian

Question 21

Why is serum creatinine high in early childhood?

Answer 21

High when still in mother because levels will be same as mother’s and will then decrease

Question 22

What is eGFR based on?

Answer 22

• serum creatinine
• age
• sex
• Caucasian or black

Question 23

When is eGFR inaccurate?

Answer 23

• people with kidney disease
• children
• pregnancy
• old age
• other ethnicities
• amputees

Question 24

True or false: eGFR overestimates true GFR

Answer 24

FALSE - underestimates