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USMLE Renal > General Pathology > Flashcards

General Pathology Flashcards

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USMLE® Step 1 flashcards
1
Q

What does an increased BUN to creatinine ratio (>15) indicate?

A

Pre-renal azotemia

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2
Q

Why in pre-renal failure is there an increased BUn to creatinine ratio?

A

RAAS system activated

- Aldosterone causes Na+, water and urea absorption

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3
Q

What will the FENa (fractional excretion of Na+) and urine osmolarity be in pre-prenal failure?

A
  • FENa < 1%
  • Urine osm >500
    This is beause tubular function remains intact
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4
Q

What will the effect of post-renal failure be on the BUN:Cr ratio?

A

Decreased BUN : Cr ratio (<15)

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5
Q

What will the effect of post-renal failure be on sodium reabsorption?

A
  • FENa > 2%

- Inability to concentrate urine (osm < 500)

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6
Q

What is acute tubular necrosis? (overview)

A
  • Injury and necrosis of tubular epithelial cells; most common cause of ARF
  • Cells lose nuclei and detach from BM
  • Necrotic cells plug tubules; obstruction decreases GFR
  • Brown, granular casts are seen in urine
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7
Q

What is the most common cause of acute renal failure?

A

Acute tubular necrosis

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8
Q

How does acute tubular necrosis decrease GFR?

A

Necrotic cells plug tubules; obstruction decreases GFR

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9
Q

What casts are seen in urine of patients with acute tubular necrosis?

A

Brown, granular casts

- Due to sloughing off of epithelial cells

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10
Q

What are the 2 types of acute tubular necrosis?

A

Ischemic and nephrotoxic

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11
Q

What is ischemic ATN generally preceded by?

A

Prerenal azotemia

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12
Q

What areas of the nephron are particularly susceptible to ischemic damage?

A

Proximal Tubule and medullary segment of TAL

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13
Q

What part of the nephron is particularly susceptible to nephrotoxic damage?

A

Proximal tubule

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14
Q

What are causes of nephrotic ATN?

A
  • Aminoglycosides
  • Heavy metals (e.g. lead)
  • Ethylene glycol (antifreeze, kids may drink)
  • Radiocontrast
  • Urate (e.g. tumour lysis syndrome)
  • Myoglobinuria (e.g. crush injury)
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15
Q

What crystals are seen in urine of a patient (usually child) who consumes ethylene glycol?

A

Calcium oxalate crystals in urine

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16
Q

What are the clinical features of ATN?

A
  • Oliguria with brown granular casts
  • Elevated BUN and creatinine
  • Hyperkalemia with metabolic acidosis
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17
Q

Is ATN reversible?

A

Yes, it can be

- Although often requires supportive dialysis since electrolyte imbalances can be fatal

18
Q

How long can it take for recovery of ATN?

A

Oliguria can persist for 2-3 weeks before recovery

- Tubular cells (stable cells) take time to reenter cell cycle and regenerate

19
Q

What is acute interstitial nephritis?

A
  • Drug induced hypersensitivity reaction of interstitium and tubules; results in acute renal failure (intrarenal)
  • Causes included NSAIDs, penicillin and diuretics
20
Q

How does acute interstitial nephritis present?

A
  • Oliguria, fever, and rash days to weeks after starting the drug
  • Resolves with cessation
21
Q

What may be seen in urine of acute interstitial nephritis?

A

Eosinophils

22
Q

What may acute interstitial nephritis progress to?

A

Renal papillary necrosis

23
Q

What does renal papillary necrosis present with?

A

Gross hematuria (due to sloughing of necrotic renal papillae) and flank pain

24
Q

What do the presence of casts indicate in urine?

A

Hematuria/pyuria is of glomerular or renal tubular origin

25
Q

What do RBC casts in urine indicate/

A
  • Glomerulonephritis

- Hypertensive emergency

26
Q

What do WBC casts in the urine indicate?

A
  • Tubulointerstitial inflammation
  • Acute pyelonephritis
  • Transplant rejection
27
Q

What are granular casts in the urine indicate?

A
  • ATN - can be ‘muddy brown’ in appearence
28
Q

What do fatty casts (oval fat bodies) in the urine indicate?

A
  • Nephrotic syndrome

- Associated with “Maltese cross” sign

29
Q

What do waxy casts in the urine indicate?

A

End-stage renal disease / CKD

30
Q

What are Hyaline casts?

A
  • Form via solidification of Tamm-Horsfall mucoprotein (uromodulin)
  • Secreted by renal tubular cells to prevent UTIs
  • Can be a normal finding w. dehydration, exercise or diuretic therapy
31
Q

What is diffuse cortical necrosis?

A
  • Acute generalised cortical infarction of both kidneys

- Likely due to a combination of vasospasm and DIC

32
Q

What is diffuse cortical necrosis associated with?

A
  • Obstetric catastrophies (e.g abruptio placentae)

- Septic shock

33
Q

How are normal phosphate levels maintained during early stages of CKD?

A
  • Increased levels of fibroblast growth factor 23 (FGF23), which promotes renal excretion of phosphate
34
Q

What are the symptoms of uremia?

A
  • Nausea
  • Anorexia
  • Encephalopathy (seen w. asterexis)
  • Pericarditis
  • Platelet dysfunction
35
Q

How is uremia managed?

A

Dialysis

36
Q

What are the consequences of renal failure?

A
  • Metabolic Acidosis
  • Dyslipidemia (esp incr triglycerides)
  • High K+
  • Uremia
  • Na+/H2O retention (HF, pulmonary edema, HTN)
  • Growth Retardation
  • Erythropoietin deficiency (anemia)
  • Renal osteodystrophy

MAD HUNGER

37
Q

What is Renal osteodystrophy?

A

Hypocalcemia, hyperphosphatemia, and failure of vit D hydroxylation associated w. CKD

  • Secondary Hyperparathyroidism
  • > Tertiary if poorly managed

High serum phosphate can bind with Ca2+ -> tissue deposits -> decreased serum Ca2+

Decreased calcitriol leads to decreased intestinal Ca2+ absorption -> subperiosteal thinning of bones

38
Q

What can cause acute interstitial nephritis?

A

5P’S

  • Pee (diuretics)
  • Pain-free (NSAIDs)
  • Penicillins and cephalosporins
  • RifamPin
  • Sulfa drugs
39
Q

What kind of infection could cause AIN?

A

Mycoplasma (secondary)

40
Q

What autoimmune diseases may cause AIN?

A
  • Sjorgen syndrome
  • SLE
  • Sarcoidosis
41
Q

Will urine osmolarity be higher in prerenal azotemia or intrinsic renal failure?

A

Prerenal will have higher
- urine osmolarity > 500

Intrinsic
- urine osmolarity < 350

42
Q

What is renal papillary necrosis associated with / caused by?

A
  • Sickle cell disease / trait
  • Acute pyelonephritis
  • Analgesics (`NSAIDs)
  • Diabetes Mellitus
    SAAD

USMLE Renal (11 decks)

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