Page 1 of 188
# SECTION I: RENAL PATHOPHYSIOLOGY
## Acute Kidney Injury & Chronic Kidney Disease
### Question 1
A 68-year-old male with a history of hypertension and diabetes presents with decreased urine
output, elevated serum creatinine (3.2 mg/dL), and BUN (45 mg/dL) over the past 48 hours. His
urine sodium is 15 mEq/L, and fractional excretion of sodium (FENa) is 0.8%. Which type of
acute kidney injury is MOST consistent with these findings?
A. Prerenal azotemia
B. Intrinsic acute tubular necrosis
C. Postrenal obstructive uropathy
D. Acute glomerulonephritis
**Correct Answer: A**
**Rationale:** Prerenal azotemia is characterized by low urine sodium (<20 mEq/L) and low
FENa (<1%), reflecting intact tubular function attempting to conserve sodium and water in
,Page 2 of 188
response to decreased renal perfusion. The elevated BUN-to-creatinine ratio (>20:1) and oliguria
further support this diagnosis. Intrinsic acute tubular necrosis typically presents with FENa >2%
and urine sodium >40 mEq/L, indicating tubular damage. Postrenal obstruction would show
normal or elevated FENa with evidence of hydronephrosis. Acute glomerulonephritis typically
presents with proteinuria, hematuria, and RBC casts.
**Distractor Analysis:**
- **B (Intrinsic ATN):** Incorrect because FENa <1% and low urine sodium suggest prerenal
physiology rather than tubular damage, which would show FENa >2%.
- **C (Postrenal obstructive):** Incorrect because there is no mention of hydronephrosis, flank
pain, or anuria; FENa would typically be elevated or variable.
- **D (Acute glomerulonephritis):** Incorrect because the presentation lacks hallmark features
such as significant proteinuria, hematuria, dysmorphic RBCs, or RBC casts.
---
### Question 2
A patient with chronic kidney disease (CKD) stage 4 has a serum creatinine of 4.5 mg/dL and an
estimated GFR of 22 mL/min/1.73m². Which of the following pathophysiologic mechanisms is
PRIMARILY responsible for the anemia commonly seen in this patient?
A. Bone marrow suppression from uremic toxins
B. Decreased erythropoietin production by damaged kidneys
C. Increased red blood cell destruction from oxidative stress
D. Impaired iron absorption due to gastrointestinal bleeding
**Correct Answer: B**
**Rationale:** The kidneys produce erythropoietin (EPO), which stimulates red blood cell
production in the bone marrow. In CKD, damaged renal interstitial fibroblasts (particularly in the
peritubular capillaries) produce less EPO, leading to anemia of chronic disease. This is the
,Page 3 of 188
primary mechanism of anemia in CKD. While uremic toxins may contribute to mild marrow
suppression (A), the predominant cause is EPO deficiency. Oxidative stress (C) and impaired
iron absorption (D) are secondary contributing factors but not the primary mechanism.
**Distractor Analysis:**
- **A (Bone marrow suppression):** Incorrect as the primary mechanism; uremic toxins may
contribute but are not the main cause of CKD anemia.
- **C (Increased RBC destruction):** Incorrect because hemolysis is not a primary feature of
CKD anemia.
- **D (Impaired iron absorption):** Incorrect; while iron deficiency can occur in CKD, it is not
the primary mechanism of the anemia.
---
### Question 3
A 55-year-old female with a history of type 2 diabetes mellitus presents with progressive edema,
hypertension, and foamy urine. Urinalysis reveals 3+ proteinuria. Serum albumin is 2.8 g/dL.
Which of the following BEST describes the pathophysiologic process underlying this patient's
presentation?
A. Reduced glomerular filtration rate with sodium retention
B. Increased glomerular capillary permeability leading to protein loss
C. Tubular dysfunction causing impaired protein reabsorption
D. Decreased hepatic synthesis of albumin
**Correct Answer: B**
**Rationale:** The presentation of significant proteinuria (>3.5 g/day), hypoalbuminemia,
edema, and hypertension is classic for nephrotic syndrome, most commonly caused by diabetic
nephropathy. The underlying pathophysiology involves increased glomerular capillary
permeability due to damage to the glomerular basement membrane and podocyte injury, leading
, Page 4 of 188
to massive protein loss in the urine. This protein loss causes hypoalbuminemia, which decreases
plasma oncotic pressure and leads to edema. Sodium retention and hypertension occur
secondarily.
**Distractor Analysis:**
- **A (Reduced GFR with sodium retention):** Incorrect; while reduced GFR may occur, the
primary pathology is increased permeability, not decreased filtration.
- **C (Tubular dysfunction):** Incorrect; the primary defect is at the glomerular level, not
tubular.
- **D (Decreased hepatic synthesis):** Incorrect; albumin is synthesized by the liver, but the low
albumin here is due to urinary loss, not decreased synthesis.
---
### Question 4
A 72-year-old male with benign prostatic hyperplasia presents with acute onset of anuria,
suprapubic pain, and a palpable distended bladder. Serum creatinine is 3.8 mg/dL (baseline 1.2
mg/dL). Which of the following is the MOST appropriate initial intervention?
A. Intravenous fluids
B. Diuretic administration
C. Bladder catheterization
D. Renal biopsy
**Correct Answer: C**
**Rationale:** This patient presents with acute urinary retention secondary to bladder outlet
obstruction from benign prostatic hyperplasia. The anuria, suprapubic pain, and palpable
distended bladder are classic findings of postrenal acute kidney injury. The most appropriate
initial intervention is bladder catheterization to relieve the obstruction and restore urine flow.
Prompt relief of obstruction can prevent permanent renal damage. Intravenous fluids (A) would
# SECTION I: RENAL PATHOPHYSIOLOGY
## Acute Kidney Injury & Chronic Kidney Disease
### Question 1
A 68-year-old male with a history of hypertension and diabetes presents with decreased urine
output, elevated serum creatinine (3.2 mg/dL), and BUN (45 mg/dL) over the past 48 hours. His
urine sodium is 15 mEq/L, and fractional excretion of sodium (FENa) is 0.8%. Which type of
acute kidney injury is MOST consistent with these findings?
A. Prerenal azotemia
B. Intrinsic acute tubular necrosis
C. Postrenal obstructive uropathy
D. Acute glomerulonephritis
**Correct Answer: A**
**Rationale:** Prerenal azotemia is characterized by low urine sodium (<20 mEq/L) and low
FENa (<1%), reflecting intact tubular function attempting to conserve sodium and water in
,Page 2 of 188
response to decreased renal perfusion. The elevated BUN-to-creatinine ratio (>20:1) and oliguria
further support this diagnosis. Intrinsic acute tubular necrosis typically presents with FENa >2%
and urine sodium >40 mEq/L, indicating tubular damage. Postrenal obstruction would show
normal or elevated FENa with evidence of hydronephrosis. Acute glomerulonephritis typically
presents with proteinuria, hematuria, and RBC casts.
**Distractor Analysis:**
- **B (Intrinsic ATN):** Incorrect because FENa <1% and low urine sodium suggest prerenal
physiology rather than tubular damage, which would show FENa >2%.
- **C (Postrenal obstructive):** Incorrect because there is no mention of hydronephrosis, flank
pain, or anuria; FENa would typically be elevated or variable.
- **D (Acute glomerulonephritis):** Incorrect because the presentation lacks hallmark features
such as significant proteinuria, hematuria, dysmorphic RBCs, or RBC casts.
---
### Question 2
A patient with chronic kidney disease (CKD) stage 4 has a serum creatinine of 4.5 mg/dL and an
estimated GFR of 22 mL/min/1.73m². Which of the following pathophysiologic mechanisms is
PRIMARILY responsible for the anemia commonly seen in this patient?
A. Bone marrow suppression from uremic toxins
B. Decreased erythropoietin production by damaged kidneys
C. Increased red blood cell destruction from oxidative stress
D. Impaired iron absorption due to gastrointestinal bleeding
**Correct Answer: B**
**Rationale:** The kidneys produce erythropoietin (EPO), which stimulates red blood cell
production in the bone marrow. In CKD, damaged renal interstitial fibroblasts (particularly in the
peritubular capillaries) produce less EPO, leading to anemia of chronic disease. This is the
,Page 3 of 188
primary mechanism of anemia in CKD. While uremic toxins may contribute to mild marrow
suppression (A), the predominant cause is EPO deficiency. Oxidative stress (C) and impaired
iron absorption (D) are secondary contributing factors but not the primary mechanism.
**Distractor Analysis:**
- **A (Bone marrow suppression):** Incorrect as the primary mechanism; uremic toxins may
contribute but are not the main cause of CKD anemia.
- **C (Increased RBC destruction):** Incorrect because hemolysis is not a primary feature of
CKD anemia.
- **D (Impaired iron absorption):** Incorrect; while iron deficiency can occur in CKD, it is not
the primary mechanism of the anemia.
---
### Question 3
A 55-year-old female with a history of type 2 diabetes mellitus presents with progressive edema,
hypertension, and foamy urine. Urinalysis reveals 3+ proteinuria. Serum albumin is 2.8 g/dL.
Which of the following BEST describes the pathophysiologic process underlying this patient's
presentation?
A. Reduced glomerular filtration rate with sodium retention
B. Increased glomerular capillary permeability leading to protein loss
C. Tubular dysfunction causing impaired protein reabsorption
D. Decreased hepatic synthesis of albumin
**Correct Answer: B**
**Rationale:** The presentation of significant proteinuria (>3.5 g/day), hypoalbuminemia,
edema, and hypertension is classic for nephrotic syndrome, most commonly caused by diabetic
nephropathy. The underlying pathophysiology involves increased glomerular capillary
permeability due to damage to the glomerular basement membrane and podocyte injury, leading
, Page 4 of 188
to massive protein loss in the urine. This protein loss causes hypoalbuminemia, which decreases
plasma oncotic pressure and leads to edema. Sodium retention and hypertension occur
secondarily.
**Distractor Analysis:**
- **A (Reduced GFR with sodium retention):** Incorrect; while reduced GFR may occur, the
primary pathology is increased permeability, not decreased filtration.
- **C (Tubular dysfunction):** Incorrect; the primary defect is at the glomerular level, not
tubular.
- **D (Decreased hepatic synthesis):** Incorrect; albumin is synthesized by the liver, but the low
albumin here is due to urinary loss, not decreased synthesis.
---
### Question 4
A 72-year-old male with benign prostatic hyperplasia presents with acute onset of anuria,
suprapubic pain, and a palpable distended bladder. Serum creatinine is 3.8 mg/dL (baseline 1.2
mg/dL). Which of the following is the MOST appropriate initial intervention?
A. Intravenous fluids
B. Diuretic administration
C. Bladder catheterization
D. Renal biopsy
**Correct Answer: C**
**Rationale:** This patient presents with acute urinary retention secondary to bladder outlet
obstruction from benign prostatic hyperplasia. The anuria, suprapubic pain, and palpable
distended bladder are classic findings of postrenal acute kidney injury. The most appropriate
initial intervention is bladder catheterization to relieve the obstruction and restore urine flow.
Prompt relief of obstruction can prevent permanent renal damage. Intravenous fluids (A) would
