Acute Renal Failure (ARF)

Question 1

Hallmark serum findings of acute renal failure

Answer 1

azotemia

increased BUN and Cr

Question 2

Hallmark single presentation symptom in acute renal failure

Answer 2

oliguria

(not producing urine)

Question 3

Pre-renal azotemia

serum findings

Answer 3

BUN:Cr > 15

b/c BUN is resorbed in the tubules and Cr is not

Question 4

1˚ etiology of pre-renal azotemia

Answer 4

decreased blood flow to kidneys

BUN reabsorbed but Cr is not

therefore BUN:Cr > 30

(normal BUN:Cr = 15)

Question 5

1˚ etiology of post-renal azotemia

Answer 5

ureter obstruction

Question 6

BUN:Cr in post-renal azotemia

Answer 6

BUN:Cr < 15 in late stages

BUN:Cr > 15 possible in early stages

increased pressure forces BUN back in early

ratio falls when tubules are damaged

Question 7

Ability to concentrate urine?

post-renal azotemia

Answer 7

inability to concentrate urine in longstanding post-renal azotemia

tubular necrosis

Question 8

Acute Tubular Necrosis

etiologies

Answer 8

• ischemic: usually after pre-renal azotemia
• nephrotoxic: drugs esp. aminoglycosides, urate esp. from tumor lysis syndrome

Question 9

Acute tubular necrosis

basic pathology

Answer 9

cells in tubules die and sluff off into tubule, plugging the tubule

Question 10

Acute tubular necrosis

basically pathopneumonic finding

Answer 10

brown, granular casts

these are from the sluffed off epithelial cells in the tubules

Question 11

BUN:Cr ratio

in acute tubular necrosis

Answer 11

BUN: Cr < 15 (ref: 15)

inability to reabsorb BUN

also inability to concentrate urine

Question 12

Clinical features of

acute tubular necrosis

Answer 12

oliguria

brown, granular casts in urine

hyperkalemia (due to inability to excrete potassium) with metabolic acidosis

Question 13

Acute interstitial nephritis

basic pathology

Answer 13

hypersensitivity reaction

usually drug induced

Question 14

Worry in acute interstitial nephritis

Answer 14

progression to acute papillary necrosis

Question 15

Pathopneumonic for

acute interstitial nepritis

Answer 15

eosinophilia

(also in urine)

because it is a hypersensitivity reaction

Question 16

Renal Papillary Necrosis

basic pathology

Answer 16

progression of acute interstitial necrosis

or

DM, sickle cell trait/disease, or severe acute pyelonephritis

Question 17

Relationship between:

BUN: Cr

and

ability to concentrate urine

Answer 17

high BUN: Cr (>15) indicates we are able to reabsorb BUN and presumably other solutes as well. this means we can concentrate our urine

low BUN:Cr (<15) indicates we are unable to reabosorb BUN and presumably other solutes. this means we are not able to concentrate our urine.

the former is seen in pre-renal azotemia, the latter in intrarenal azotemia. post-renal azotemia begins with the former and progresses to the latter