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Flashcards in Acute Kidney Injury Deck (26):

In acute kidney injury, there is a reduction in _____ resulting in ______ developing over days

GFR; azotemia


What are common causes of acute kidney injury?

Renal ischemia or toxins


How is kidney size affected in AKI?

Kidney size is usually preserved


What are some of the diagnostic criteria for AKI?

  • An abrupt (within 48 hours) reduction in kidney function defined as
    • An absolute increase in serum creatinine level of 0.3 mg/dl or
    • A percentage increase in serum creatinine level of ≥ 50% or
    • A reduction in urine output < 500 mL in 24 hours


Define the following:

  • Oliguria:
  • Azotemia:
  • Uremia:

  • Oliguria: Urin output < 400-500 ml/day
  • Azotemia: Elevation of nitrogen waste products related to insufficient filtering of blood by the kidneys
  • Uremia: The illness accompanying kidney failure which results from the toxic effects of abnormally high concentrations of nitrogenous substances in the blood


Serum creatinine levels are inversely proportionate to  ___


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What are the limitations of creatinine compared to inulin?

Unlike inulin, creatinine is also secreted in the nephron and creatinine clearance overestimates GFR


What is BUN and when is it used to diagnose renal disease?

Blood Urea Nitrogen - nitrogenous waste product of protein metabolism

Useful in conjunction with creatinine in the differential diagnosis of renal disease - less accurate than creatinine due to variation in protein intake, catabolic rate, and tubular reabsorption


How are casts formed and how do they present in acute tubular necrosis?

Casts are caused by the trapping of cellular elements in a matrix of protein secreted by renal tubules

Granular casts - muddy brown urine - are seen in cases of acute tubular necrosis

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Autoregulation of GFR and RBF is effective between the blood pressures of __ and __

80 and 160

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What GFR autoregulation mechanisms can compensate for decreased perfusion pressure?

Increased vasodilatory prostaglandins - dilate afferent arterioles

Increased angiotensin II - Constrict efferent arteriole


With impaired autoregulation _____ _____ has greater effect on GFR

arterial pressure


What are the three categories of AKI?

  • Pre-renal: imparied effective renal perfusion
  • Renal: intrinsic renal disease
  • Post renal: obstruction of urinary flow


Pre-renal AKI consists of decreased GFR without _____ or _____ injury to tubules

ischemic or nephrotoxic


How does pre-renal AKI lead to oliguria?

Decreased effective renal perfusion → increased Ang II and vasopressin → increased reabsorption of sodium (at proximal tubule) and water → concentrated urine → oliguria


Pre-renal AKI is associated with increased reabsorption of urea

Elevation of ____is out of proportion to creatinine?

elevation of BUN is out of proportion to creatinine (>20:1)


How does the tubular epithelium appear in pre-renal AKI?



What is the most common cause of renal AKI?

Acute tubular necrosis


What are some causes of Renal AKI?

  • ATN
  • Inflammation: glomerulonephritis, tubulointerstitial nephritis, vasculitis
  • Embolism, thrombosis, thrombotic miroangiopathy
  • Neoplasms: infiltrating tumors


What are some morphologic features of acute tubular necrosis (ATN)?

  • Tubular dilation
  • Attenuation of tubular epithelium
  • Loss of epithelial cell brush border
  • Granular cast material
  • Mitotic figures (regenerative change)


How do tubules regenerate after ATN?

Sublethally injured tubular epithelial cells repopulate the tubules by:

De-differentiation → proliferation → migration → re-establishing cell polarity

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What are some causes of Post-renal AKI?

Bladder outlet obstruction

Ureteral obstruction


How many kidneys are affected in Post-Renal AKI?



What is hydronephrosis (in post renal AKI)?

Distension and dilation of the renal pelvis calyces


How can fractional excretion of sodium (FENa) distinguish pre-renal AKI from acute tubular necrosis?

  • In the setting of volume depletion urine Na reabsorption should be increased in the proximal tubules → FENa < 1%
  • If the proximal tubules are injured (ATN), sodium reabsorption will be impaired → FENa > 2%


How do you calculate FENa?

FENa = [(UNa x PCr)/ (PNa x Ucr)] x 100

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