Evaluating Renal Function

Question 1

Which arteriole enters the glomerulus and which one exits?

Answer 1

Enters: afferent
Exits: efferent

Question 2

Out of these three: thiazides, loop diuretics, and K+ sparing diuretics, which one is the most potent?

Answer 2

loops

Question 3

Where do K+ sparing and thiazides work on the nephron?

Answer 3

thiazides = distal tubules

k+ sparing = distal and collecting duct

Question 4

What is GFR? What is the gold standard for measuring GFR? Why is it the gold standard?

Answer 4

GFR = glomerular filtration rate
It is the amount of blood filtered in the kidney each minute

The gold standard is clearance of inulin (natural sugar) bc it is solely filtered in the glomerulus and not secreted, reabsorbed and metabolized in the kidney

Question 5

Creatinine clearance is also a good measure but why is it less accurate?

Answer 5

Some of it is secreted into the tubules and leads to an overestimation of about 10%

Question 6

When comparing age, gender, and body size, which factors contribute to larger GFRs?

Answer 6

High GFR: Male, young, and big body

Lower GFR: Women, old, and small body

Question 7

What is the average GFR for males 20-30? 70 - 80? Females?

Answer 7

Males
20 - 30 = 110mL/min
70 - 80 = 65mL/min

Females
20 - 30 = 100mL/min
70 - 80 = 50mL/min

Question 8

When screening for kidney disease, what are the rough ranges of GFR for disease?

Answer 8

60 - 120 = normal
15 - 60 = kidney disease
<15 = kidney failure

Question 9

What are some other biomarkers that can estimate kidney function?

Answer 9

Cystatin - C
Iothalamate
Radiolabeled markers

Question 10

What are the equations for calculating GFR and creatinine clearance?

Answer 10

CrCL
- Cockcroft - Gault

GFR

• MDRD Equation
• CKD - EPI
• Schwartz Equation (children)

Question 11

What are some key adjustments that need to be made to the Cockcroft - Gault equation?

Answer 11

• Do not round up in elderly patients to 1.0, use the actual SCr value
• Use ABW if patient is not obese (if patient is obese or >30% above IBW, then use IBW)

Question 12

How do you calculate IBW?

Answer 12

IBW
[50 + (2.3 * inches > 60 inches)] for men
[45 + (2.3 * inches > 60 inches)] for women

Question 13

What are the advantages and disadvantages of the Cockcroft - Gault equation?

Answer 13

Advantages - easy and rapid

Disadvantages - not reliable in extremes of age and weight

Question 14

In cases where we would treat an obese patient on chemotherapy, how would we go about measuring his/her renal function? Show the equation

Answer 14

24 - hr urine collection for CrCl for narrow therapeutic index drugs

CrCl =( [Urine Cr] * Urine Volume) / ([serum Cr] * 1440 min)

Question 15

What are CrCl and GFR used for?

Answer 15

CrCl is mainly used for adjustment of doses

GFR is mainly used for staging kidney disease

Question 16

Which equation for GFR is more accurate above GFRs of 60mL/min/1.73m2?

Answer 16

CKD - EPI

Question 17

What are the advantages and disadvantages of the MDRD and CKD-EPI equations?

Answer 17

Advantages:

• more accurate than C-G
• covers good spectrum of kidney dysfunction
• not affected by height, weight extremes

Disadvantages:
- normalized GFR to 1.73m2 - need to scale for weight differences (obese or thin)

Question 18

How do we calculate children’s GFR? What does it take into account?

Answer 18

GFR = [k * height (cm)] / serum creatinine (mg/dL)
Pre-term babies k = 0.33; full-term babies k = 0.45
Ages 1 - 12 k = 0.55