Acute & Chronic Renal Failure

Question 1

Name some causes of prerenal azotemia.

Answer 1

Decreased blood flow to kidneys:

• Dehydration
• Hemorrhage
• Sepsis
• Cardiac failure

Question 2

What are indicators of normal tubular function?

Answer 2

1. Fractional excretion of sodium < 1%

2. Urine osmolality > 500 mOsm/kg

Question 3

Why is the BUN:Cr ratio > 15 in prerenal azotemia?

Answer 3

Low blood flow –> activates RAAS –> aldosterone release –> increased water & Na absorption –> more BUN flows into blood (Cr cannot be reabsorbed)

Question 4

What are the key characteristics in prerenal azotemia?

Answer 4

Decreased GFR, azotemia, oliguria

Question 5

What is the difference between early and late stage obstruction of urinary tract downstream of kidney?

Answer 5

1. Early Stage: BUN:Cr > 15 because tubular pressure forces BUN into blood; intact tubular function
2. Late Stage: BUN:Cr < 15 because tubules no longer intact + FENa > 2% & unable to concentrate urine

Question 6

What is the most common cause of acute renal failure?

Answer 6

Acute tubular necrosis

Question 7

What are brown, granular casts indicative of?

Answer 7

Acute tubular necrosis. Tubular epithelial cells undergo necrosis and plug tubules

Question 8

Describe lab findings & clinical features seen in acute tubular necrosis.

Answer 8

1. BUN:Cr < 15 because dysfunctional tubular epithelium –> elevated plasma BUN & Cr
2. FENa > 2%
3. Urine Osm < 500 mOsm/kg
4. Oliguria with brown, granular casts
5. Hyperkalemia with metabolic acidosis

Question 9

What are the two main etiologies underlying acute tubular necrosis? Along which part of the nephron do these two commonly occur?

Answer 9

1. Ischemic (progression of prerenal azotemia); proximal tubule & medullary TAL
2. Nephrotoxic; proximal tubule

Question 10

What are some common causes of nephrotoxic acute tubular necrosis?

Answer 10

1. Aminoglycosides (most common)
2. Heavy metals - lead
3. Myoglobinuria - myoglobin released from crush injury to muscle
4. Ethylene glycol - blue color & sweet; accidentally taken by kids; see oxalate crystals in urine
5. Radiocontrast dye
6. Urate - tumor lysis syndrome; leukemia patients taking chemo –> rapid break down of cells –> increased uric acid –> damages tubules

Question 11

What steps can be taken to reduce the risk of urate-induced ATN?

Answer 11

Hydration and allopurinol intake before starting chemotherapy

Question 12

What does the treatment of acute tubular necrosis involve?

Answer 12

Reversible by treating underlying cause; may require supportive dialysis

Question 13

Why is the recovery time from acute tubular necrosis long (2-3 weeks) if it is reversible?

Answer 13

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

Question 14

List some causes of acute interstitial nephritis.

Answer 14

Drug-induced hypersensitivity so drugs! But also infections

1. NSAIDs
2. Penicillin
3. Diuretics
4. Rifampin
5. Sulfonamides
6. Infections (EBV, CMV, TB; less common)

Question 15

What do people with acute interstitial nephritis present with? When do these symptoms start?

Answer 15

1. Oliguria
2. Fever
3. Rash
4. Eosinophils in urine (possibly)
5. Granular casts - RBCs & WBCs in urine sediment
6. Inflammatory infiltrate in interstitium
   * Days to weeks after drug intake

Question 16

What can acute interstitial nephritis progress to?

Answer 16

Renal papillary necrosis

Question 17

What do people with renal papillary necrosis present with?

Answer 17

Gross hematuria and flank pain

Question 18

What are some causes of renal papillary necrosis?

Answer 18

1. Chronic analgesic abuse (phenacetin or aspirin)
2. Diabetes mellitus
3. Sickle cell trait or disease
4. Severe acute pyelonephritis

Question 19

What are the three most common causes of chronic renal failure?

Answer 19

1. Diabetes mellitus
2. HTN
3. Glomerular disease