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USMLE Renal > General Pathology > Flashcards

General Pathology 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
What do RBC casts in urine indicate/
- Glomerulonephritis | - Hypertensive emergency
26
What do WBC casts in the urine indicate?
- Tubulointerstitial inflammation - Acute pyelonephritis - Transplant rejection
27
What are granular casts in the urine indicate?
- ATN - can be 'muddy brown' in appearence
28
What do fatty casts (oval fat bodies) in the urine indicate?
- Nephrotic syndrome | - Associated with "Maltese cross" sign
29
What do waxy casts in the urine indicate?
End-stage renal disease / CKD
30
What are Hyaline casts?
- 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
What is diffuse cortical necrosis?
- Acute generalised cortical infarction of both kidneys | - Likely due to a combination of vasospasm and DIC
32
What is diffuse cortical necrosis associated with?
- Obstetric catastrophies (e.g abruptio placentae) | - Septic shock
33
How are normal phosphate levels maintained during early stages of CKD?
- Increased levels of fibroblast growth factor 23 (FGF23), which promotes renal excretion of phosphate
34
What are the symptoms of uremia?
- Nausea - Anorexia - Encephalopathy (seen w. asterexis) - Pericarditis - Platelet dysfunction
35
How is uremia managed?
Dialysis
36
What are the consequences of renal failure?
- 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
What is Renal osteodystrophy?
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
What can cause acute interstitial nephritis?
5P'S - Pee (diuretics) - Pain-free (NSAIDs) - Penicillins and cephalosporins - RifamPin - Sulfa drugs
39
What kind of infection could cause AIN?
Mycoplasma (secondary)
40
What autoimmune diseases may cause AIN?
- Sjorgen syndrome - SLE - Sarcoidosis
41
Will urine osmolarity be higher in prerenal azotemia or intrinsic renal failure?
Prerenal will have higher - urine osmolarity > 500 Intrinsic - urine osmolarity < 350
42
What is renal papillary necrosis associated with / caused by?
- Sickle cell disease / trait - Acute pyelonephritis - Analgesics (`NSAIDs) - Diabetes Mellitus SAAD

USMLE Renal (11 decks)

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