renal function tests

Question 1

a normal GFR is

Answer 1

> 90ml/min/1.73m2

Question 2

a GFR in a young adult will be

Answer 2

120ml/min/1.73m3
will decrease by 10 every decade after 29

Question 3

creatinine is a metabolite of

Answer 3

creatine

Question 4

creatinine is removed by

Answer 4

glomerular filtration
produced at a relatively constant rate and filtered by the glomeruli and can be used to measure eGFR

Question 5

when does serum creatinine start to rise

Answer 5

serum creatinine levels do not start rising until the GFR is reduced by approx 50%
if the GFR is >60, serum creatinine cannot be used to assess kidney function

Question 6

why does serum creatinine not initially rise in decreased glomrular filtration

Answer 6

a compensatory increase in proximal tubule secreton in stages of decreased glomerular filtration results in a slower rise in creatinine

Question 7

reasons serum creatinine might be high

Answer 7

high protein diet
high muscle mass
rigorous exercise

Question 8

creatinine clearance is measured by

Answer 8

measuring creatinine in the urine over a 24 hours period

Question 9

creatinine clearance being used to measure GFR

Answer 9

slightly oveerestimates the GFR because of minimal creatinine secretion in the proximal tubules

Question 10

formula for eGFR

Answer 10

creatinine(urine)xV/creatinine(plasma) = eGFR

Question 11

serum cycstatin C is

Answer 11

a more precise indicator of the GFR than serum creatinine
produced by all nucleated cells
analysis is complex and expensivee so not routinely ordered

Question 12

blood urea nitrogen

Answer 12

a waste product produced by the liver in the urea cycle after protein degredation
filtered and excreted by the kidneys
elevated with reduced GFR, high protein diet and protein catabolism

Question 13

BUN/creatinine ratio

Answer 13

can help diagnose underlying cause

Question 14

BUN/creatinine ratio 10:1 - 20:1

Answer 14

can be normal or indicate a post renal cause

Question 15

BUN/creatinine ratio >20:1

Answer 15

indicates prerenal cause: urea reabsorption is increased, which is typical in patients with dehydration or pypoperfusion

Question 16

perfusion deficit to the kidneys causes

Answer 16

decreased urinary filtration and slower urine flow within the renal tubules
the prolonged urine passage allows for the renal tubular cells to reabsorb more urea than usual while creatinine is not reabsorbed

Question 17

BUN/creatinine ratio <15:1

Answer 17

indicates intrarenal cause
renal damage causes decrease urea resorption

Question 18

fractional excretion of sodium

Answer 18

FeNa
percentge of the glomerular filtered sodium (Na filtered) that is eventual excrete in the urine (Na excreted)

Question 19

what is fractional excretion of sodium used for

Answer 19

establish cause of AKI

Question 20

low FeNa in AKI

Answer 20

<1%
indicates prerenal cause
(renal hypoperfusion)

Question 21

high FeNa in AKI

Answer 21

> 2%
indicates intrarenal aetiology

Question 22

low FeNa in hypotonic hyponatraemia

Answer 22

extrarenal cause

Question 23

high FeNa in hypotonic hyponatraemia

Answer 23

renal cause

Question 24

ANCA antibodies are an indication of

Answer 24

GN

Question 25

muddy brown casts are specific for

Answer 25

acute tubular necrosis

Question 26

red blood cell casts indicate

Answer 26

GN

Question 27

white blood cell casts indicate

Answer 27

pylonephritis