Acute kidney injury

Question 1

definition: acute kidney injury

Answer 1

reduction in glomerular filtration rate resulting in azotemia developing over a few times

Question 2

acute kidney injury is commonly due to __________-

Answer 2

renal ischemia or toxins

Question 3

is AKI reversible or irreversible?

Answer 3

reversible

Question 4

diagnostic criteria for AKI

Answer 4

• absolute increase in serum creatinine level of 0.3 mg/dL or more
• over 50% increase in serum creatinine
• reduction of urine output less than 500 mL in 24 hr

Question 5

definition: azotemia

Answer 5

elevation of nitrogenous waste products related to insufficient filtering of blood by the kidneys

Question 6

definition: oliguria

Answer 6

less than 400-500 mL / day

Question 7

definition: anuria

Answer 7

less than 50 mL / day

Question 8

what is the key test to understanding what is going on with the kidney?

Answer 8

UA

Question 9

creatinine clearance can be used to estimate _____

Answer 9

GFR

Question 10

serum creatinine levels are inversely proportional to _____

Answer 10

GFR

Question 11

creatinine clearance _________ (underestimates / overestimates) GFR

Answer 11

overestimates

Question 12

BUN is a less accurate indicator of GFR than creatinine due to variation in what 3 factors?

Answer 12

• protein intake
• catabolic rate
• tubular reabsorption

Question 13

what is the cause of urine casts?

Answer 13

trapping of cellular elements in a matrix of protein secreted by renal tubule cells

Question 14

what type of casts are seen in acute tubular necrosis? what is the appearance of the urine?

Answer 14

• granular casts

- “muddy brown” urine

Question 15

• age
• NSAIDs
• CKD

these affect which glomerular arteriole? how?

Answer 15

afferent (prevent dilation)

Question 16

• ACE inhibitors
• ARBs

these affect which glomerular arteriole? how?

Answer 16

efferent (prevent angiotensin II mediated vasoconstriction)

Question 17

what are the three types of AKI?

Answer 17

• pre-renal
• renal
• post-renal

Question 18

what is the etiology of pre-renal AKI? what is one major condition associated with it?

Answer 18

• impaired effective renal perfusion

- volume depletion

Question 19

what is the etiology of renal AKI? what is one major condition associated with it?

Answer 19

• intrinsic renal disease (glomerular, tubular, interstitial, vascular)
• acute tubular necrosis

Question 20

what is the etiology of post-renal AKI? what is one major condition associated with it?

Answer 20

• obstruction of urinary flow

- BPH, tumor

Question 21

prerenal AKI has decreased GFR ________ (with / without) ischemic or nephrotoxic injury to tubules

Answer 21

without

Question 22

what is the BUN : creatinine ratio for prerenal AKI?

Answer 22

over 20 : 1

Question 23

what type of casts can be seen in prerenal (volume depleted) AKI?

Answer 23

hyaline

Question 24

what is the most common cause of renal AKI?

Answer 24

acute tubular necrosis (ATN)

Question 25

what are the morphologic features of ATN?

Answer 25

- tubular dilation - attenuation of tubular epithelium - loss of epithelial cell brush border - granular cast material - mitotic figures

Question 26

can tubule cells regenerate following ATN?

Answer 26

yes

Question 27

what is obstructive uropathy?

Answer 27

obstruction of the urinary tract at any level that affects both kidneys

Question 28

what should be ruled out in all patients with oliguria?

Answer 28

obstructive uropathy (post-renal AKI)

Question 29

what is hydronephrosis?

Answer 29

distension and dilation of the renal pelvis calyces

Question 30

what test is used to differentiate prerenal AKI from ATN?

Answer 30

assessment of urine sodium excretion

Question 31

what test do you use to exclude postrenal AKI?

Answer 31

renal imaging (US, CT)

Question 32

how is fractional excretion of sodium expressed?

Answer 32

amount of sodium excreted over amount of sodium filtered by glomeruli

Question 33

in the setting of volume depletion, urine Na reabsorption should be _________ (increased / decreased) in the proximal tubules what would the FENa be?

Answer 33

- increased | - FENa less than 1%

Question 34

if the proximal tubules are injured via ATN, how is sodium handling affected? what is the FENa result?

Answer 34

- reabsorption will be impaired? | - FENa over 2%

Question 35

what lab helps to differentiate between prerenal azotemia and ATN?

Answer 35

FENa

Question 36

what is the FENa level in ATN? prerenal azotemia?

Answer 36

- ATN: over 2% | - prerenal azotemia: less than 1%