diagnostics of AKI - amboss

Question 1

a diagnosis of AKI can be made based on

Answer 1

acute increase in serum creatinine and/or decrease in urine output

Question 2

approach to diagnosis of AKI

Answer 2

compare current and previous creatinine levels to determine if the process is acute
perform staging
determine if prerenal, intrarenal or post renal
consider further testing for underlying causes.

Question 3

in absense of previously documented creatinine levels

Answer 3

stable creatinine levels with findings such as chronic anaemia and small hyperechoic kidneys on US suggest CKD

Question 4

diagnostic criteria for acute kidney injury

Answer 4

increase in serum creatinine by > 0.3mg/dL within 48 hours
increase in serum creatinine to >1.5 times baseline level in 7 days
decrease in urine output to <0.5mL/kg/hour for >6 hours

Question 5

what does urine osmolality tell you

Answer 5

> 500 mOsm/kg means prerenal
< 350 mOsm/kg means intrinsic or postrenal

Question 6

BUN:creatinine ratio

Answer 6

high in prerenal >20:1
low in intrinsic <15:1
varies in post renal

Question 7

FENa

Answer 7

The percentage of glomerular filtered sodium (Na) that is excreted in the urine in relation to filtered creatinine (Cr).
<1% in prerenal
>2-3% in intrinsic
varies in post renal

Question 8

FEUrea

Answer 8

The percentage of glomerular filtered urea (Ur) that is excreted in the urine in relation to filtered creatinine (Cr)
<35% prerenal
>50% intrinsic
varies in post renal

Question 9

urine sediment in prerenal

Answer 9

hyaline casts in prerenal

Question 10

urine sediment in intrinsic

Answer 10

renal tubular epithelial cells or pigmented casts, RBC casts, fatty casts, WBC casts in intrinsic

Question 11

urine sediment in postrenal

Answer 11

hematuria (stones, bladder cancer, clots)
absent (neurogenic bladder)

Question 12

blood study findings of prerenal AKI

Answer 12

elevated serum creatinine
serum BUN:creatinine ratio > 20:1 (prolonged urine passage time causes increased urea resorbtion)

Question 13

urine study findings of prerenal AKI

Answer 13

normal urinalysis
low urinary soium and urea excretion
- low FENa
- low FEUrea
high urine osmolality
hyaline casts due to concentrated urine in the setting of low renal perfusion

Question 14

intrinsic AKI blood study findings

Answer 14

elevated serum creatinine concentration rapidly rising serum creatinine level
BUN:creatinine ratio <15:1 (tubular dysfunction leads to impaired resorbtion of urea)

Question 15

intrinsic AKI urine study findings

Answer 15

high urinary sodium and urea excretion (due to impaired ability to resorb)
- high urine sodium
- high FENa
- high FEUrea
low urine osmolality (due to inability to concentrate urine)
urine sediment: renal tubular epithelial cells or granular, muddy brown, or pigmented casts

Question 16

post renal AKI blood study findings

Answer 16

elevated serum creatinine concentration in bilateral obstruction
BUN:creatinine ratio varies, usually normal

Question 17

post renal AKI urine study findings

Answer 17

normal urinalysis eg. when due to neurogenic bladder
hematuria eg. when due to stones, bladder cancer, clots
urine osmolality varies

Question 18

imagining for post renal AKI

Answer 18

renal US if there is clinical suspicion for hyronehrosis
non contrast CT if positive US or is suspicion for obstruction remainns high