[2] Renal Function Tests

Question 1

Where is Erythropoietin produced in the Kidneys?

Answer 1

Peritubular Capillaries of the Renal Cortex

Question 2

How much urine do you produce in a day?

Answer 2

1-2L

Question 3

What monitors Na+ and Cl- concentration in the final portion of the loop of Henle

Answer 3

Macula Densa

Question 4

“Gold Standard” for GFR Assessment

Why?

Answer 4

Inulin

Completely filtered by the glomerulus

Question 5

23 yo medical student (55kg) collects her urine for 24 hours and has blood drawn.

Her serum creatinine is 0.6mg/dL
24 hour urine volume is 2L

Is her kidney function normal?

Answer 5

Total Urine Volume: 2L = 2000mL = 20 dL
U: 50mg/dL
Total U: 50mg/dL * 20dL = 1,000mg

Ccr = (1,000mg/1,440min) / (0.6mg/dL)*(100) = 115 mL/min

Yes, kidney function is normal

Question 6

Cockroft-Gault Formula

Answer 6

[(140-Age)Lean Body Weight in kg.] / 72Serum Creatinine

Note: Multiply by 0.85 for women

Question 7

GFR Rates of Different Stages of ESRD

Answer 7

Stage 1: >90
Stage 2: 60-90
Stage 3: 30-60
Stage 4: 15-30
Stage 5: <15 or on Dialysis

Question 8

Effect of Cimetidine on Serum Creatinine

Answer 8

Increased: Inhibits tubular secretion

Question 9

When do you not test with Cystatin C

Answer 9

Patients with thyroid disease

Question 10

Benefits of Cystatin C over Creatinine

Answer 10

Detects CKD earlier than creatinine

More sensitively predicts earlier complications of CKD

Question 11

What would strongly suggest renal/glomerular origin of hematuria?

Answer 11

Dysmorphic RBCs