NEPHROLOGY COMPREHENSIVE EXAM – KDIGO 2026
/ABIM–ESENeph – 2026/2027 EDITION COMPREHENSIVE QUESTIONS
WITH VERIFIED ANSWERS AND DETAILED RATIONALES
LATEST UPDATE
SECTION 1: SODIUM AND WATER ABNORMALITIES (Questions 1–16)
Q1. A 68-year-old man with heart failure and HTN presents with confusion. Meds:
lisinopril, furosemide, metoprolol. Labs: Na 118, K 4.2, Cl 88, HCO3 24, BUN 22,
Cr 1.1, serum osmolality 248, urine osmolality 580. What is the diagnosis?
A) Psychogenic polydipsia
B) SIADH
C) Adrenal insufficiency
D) Hypothyroidism
E) Diuretic-induced hyponatremia
Answer: B
Explanation: Hypotonic hyponatremia (serum Osm < 275) with inappropriately
concentrated urine (Uosm > 100) defines SIADH. Uosm of 580 indicates ongoing
ADH action despite low serum Osm. Diuretics usually lower Uosm. Adrenal
insufficiency and hypothyroidism are less likely here.
Q2. A 72-year-old woman on HCTZ, sertraline, alendronate has Na 112, serum
Osm 240, urine Osm 520, urine Na 85. She is lethargic and nauseated. What is the
most appropriate initial management?
A) 3% hypertonic saline bolus
B) Fluid restriction to 1 L/day
C) Demeclocycline
D) Normal saline 100 mL/hr
E) Stop sertraline and fluid restriction
Answer: E
Explanation: This is sertraline-induced SIADH (euvolemia, Uosm > 100, UNa > 40).
Remove offending drug and fluid restrict. Hypertonic saline is reserved for
severe symptoms (seizures/coma) or Na < 120 with symptoms. Normal saline
would
worsen hyponatremia in SIADH.
Q3. A 45-year-old with small cell lung cancer has Na 118, serum Osm 245, urine
1
,Osm 600, urine Na 90. He is asymptomatic. What is the best treatment?
A) Hypertonic saline 50 mL bolus
B) Fluid restriction to 800 mL/day
C) Demeclocycline 600 mg BID
D) Conivaptan
E) Normal saline infusion
Answer: B
Explanation: Asymptomatic chronic SIADH is managed with fluid restriction
(typically 500–1000 mL/day). Demeclocycline or vasopressin receptor antagonists
are second-line. Hypertonic saline is for symptomatic or acute severe
hyponatremia.
Q4. A 58-year-old alcoholic presents with seizures. Na 108, serum Osm 220, urine
Osm 80, urine Na 12. What is the diagnosis?
A) SIADH
B) Cerebral salt wasting
C) Psychogenic polydipsia
D) Beer potomania
E) Adrenal crisis
Answer: D
Explanation: Beer potomania causes profound hypotonic hyponatremia with
dilute urine (Uosm < 100) due to low solute intake combined with excessive
free water intake. Urine Na is low reflecting appropriate renal sodium
conservation. Psychogenic polydipsia can also give dilute urine but usually
less severe Na depression.
Q5. A 65-year-old post-operative day 1 after hip replacement has Na 125,
serum Osm 260, urine Osm 550, urine Na 30. BP 130/80, HR 72, no edema.
What is the cause?
A) Post-operative SIADH
B) Hypovolemic hyponatremia
C) Hypervolemic hyponatremia
D) Reset osmostat
E) Glucocorticoid deficiency
Answer: A
Explanation: Post-operative state is a classic cause of SIADH (pain, stress,
medications). Euvolemia (normal BP, HR, no edema) with concentrated urine and
elevated UNa (> 20–30) supports SIADH.
2
,Q6. A 34-year-old marathon runner presents with confusion after drinking
copious
water during race. Na 118, serum Osm 240, urine Osm 60, urine Na 8. What is the
most appropriate immediate treatment?
A) 3% saline at 50 mL/hour
B) Oral salt tablets
C) Fluid restriction
D) IV normal saline
E) Desmopressin
Answer: A
Explanation: Exercise-associated hyponatremia with encephalopathy (confusion)
requires hypertonic saline. The urine is maximally dilute (Uosm < 100) due to
suppressed ADH, but the free water load overwhelms excretion.
Q7. A 70-year-old with CHF (EF 25%) has Na 122, serum Osm 255, urine Osm 400,
urine Na 20. Edema, JVP 14 cm, crackles. What is the primary mechanism?
A) SIADH
B) Effective arterial volume depletion with non-osmotic ADH release
C) Primary polydipsia
D) Renal salt wasting
E) Hypothyroidism
Answer: B
Explanation: In heart failure, decreased effective arterial volume stimulates
baroreceptors, causing non-osmotic ADH release and water retention despite
hypervolemia. Urine Na is low due to reduced effective volume.
Q8. A 62-year-old with cirrhosis and ascites has Na 125, urine Osm 450, urine Na
12. What is the safest initial therapy for hyponatremia?
A) Vaptans
B) Fluid restriction
C) Hypertonic saline
D) Albumin infusion
E) Loop diuretics
Answer: B
Explanation: Fluid restriction is first-line for cirrhotic hyponatremia.
Vaptans are used with caution due to risk of rapid correction. Hypertonic
saline is reserved for severe symptoms.
3
, Q9. A patient with SIADH is treated with fluid restriction but Na drops from
125 to 120. What is the next best step?
A) Demeclocycline
B) Tolvaptan 15 mg daily
C) Hypertonic saline bolus
D) Increase fluid restriction to 500 mL
E) IV normal saline
Answer: B
Explanation: Tolvaptan is indicated for euvolemic/hypervolemic hyponatremia
resistant to fluid restriction. Demeclocycline is an alternative but has
nephrotoxicity. Hypertonic saline is for symptomatic hyponatremia.
Q10. A 48-year-old with traumatic brain injury has Na 130, urine Osm 780, urine
Na 120. What distinguishes SIADH from cerebral salt wasting (CSW)?
A) Serum uric acid
B) Urine output
C) BUN/Cr ratio
D) Response to normal saline
E) Serum potassium
Answer: D
Explanation: CSW improves with volume repletion (normal saline) and is a
hypovolemic state. SIADH worsens with saline (urine Na excretion increases)
and is euvolemic. Low uric acid and high FEurate occur in both.
Q11. A 55-year-old with schizophrenia polydipsia has Na 119, serum Osm 242,
urine Osm 50, urine Na 15. What is the mechanism?
A) ADH excess
B) Primary polydipsia with dilute urine
C) Reset osmostat
D) Renal failure
E) Diabetes insipidus
Answer: B
Explanation: Psychogenic polydipsia leads to massive free water intake,
suppressing ADH and producing maximally dilute urine (Uosm < 100).
Differentiate from nephrogenic DI by normal response to water deprivation.
Q12. A 67-year-old with pneumonia has Na 128, serum Osm 265, urine Osm 510,
4
/ABIM–ESENeph – 2026/2027 EDITION COMPREHENSIVE QUESTIONS
WITH VERIFIED ANSWERS AND DETAILED RATIONALES
LATEST UPDATE
SECTION 1: SODIUM AND WATER ABNORMALITIES (Questions 1–16)
Q1. A 68-year-old man with heart failure and HTN presents with confusion. Meds:
lisinopril, furosemide, metoprolol. Labs: Na 118, K 4.2, Cl 88, HCO3 24, BUN 22,
Cr 1.1, serum osmolality 248, urine osmolality 580. What is the diagnosis?
A) Psychogenic polydipsia
B) SIADH
C) Adrenal insufficiency
D) Hypothyroidism
E) Diuretic-induced hyponatremia
Answer: B
Explanation: Hypotonic hyponatremia (serum Osm < 275) with inappropriately
concentrated urine (Uosm > 100) defines SIADH. Uosm of 580 indicates ongoing
ADH action despite low serum Osm. Diuretics usually lower Uosm. Adrenal
insufficiency and hypothyroidism are less likely here.
Q2. A 72-year-old woman on HCTZ, sertraline, alendronate has Na 112, serum
Osm 240, urine Osm 520, urine Na 85. She is lethargic and nauseated. What is the
most appropriate initial management?
A) 3% hypertonic saline bolus
B) Fluid restriction to 1 L/day
C) Demeclocycline
D) Normal saline 100 mL/hr
E) Stop sertraline and fluid restriction
Answer: E
Explanation: This is sertraline-induced SIADH (euvolemia, Uosm > 100, UNa > 40).
Remove offending drug and fluid restrict. Hypertonic saline is reserved for
severe symptoms (seizures/coma) or Na < 120 with symptoms. Normal saline
would
worsen hyponatremia in SIADH.
Q3. A 45-year-old with small cell lung cancer has Na 118, serum Osm 245, urine
1
,Osm 600, urine Na 90. He is asymptomatic. What is the best treatment?
A) Hypertonic saline 50 mL bolus
B) Fluid restriction to 800 mL/day
C) Demeclocycline 600 mg BID
D) Conivaptan
E) Normal saline infusion
Answer: B
Explanation: Asymptomatic chronic SIADH is managed with fluid restriction
(typically 500–1000 mL/day). Demeclocycline or vasopressin receptor antagonists
are second-line. Hypertonic saline is for symptomatic or acute severe
hyponatremia.
Q4. A 58-year-old alcoholic presents with seizures. Na 108, serum Osm 220, urine
Osm 80, urine Na 12. What is the diagnosis?
A) SIADH
B) Cerebral salt wasting
C) Psychogenic polydipsia
D) Beer potomania
E) Adrenal crisis
Answer: D
Explanation: Beer potomania causes profound hypotonic hyponatremia with
dilute urine (Uosm < 100) due to low solute intake combined with excessive
free water intake. Urine Na is low reflecting appropriate renal sodium
conservation. Psychogenic polydipsia can also give dilute urine but usually
less severe Na depression.
Q5. A 65-year-old post-operative day 1 after hip replacement has Na 125,
serum Osm 260, urine Osm 550, urine Na 30. BP 130/80, HR 72, no edema.
What is the cause?
A) Post-operative SIADH
B) Hypovolemic hyponatremia
C) Hypervolemic hyponatremia
D) Reset osmostat
E) Glucocorticoid deficiency
Answer: A
Explanation: Post-operative state is a classic cause of SIADH (pain, stress,
medications). Euvolemia (normal BP, HR, no edema) with concentrated urine and
elevated UNa (> 20–30) supports SIADH.
2
,Q6. A 34-year-old marathon runner presents with confusion after drinking
copious
water during race. Na 118, serum Osm 240, urine Osm 60, urine Na 8. What is the
most appropriate immediate treatment?
A) 3% saline at 50 mL/hour
B) Oral salt tablets
C) Fluid restriction
D) IV normal saline
E) Desmopressin
Answer: A
Explanation: Exercise-associated hyponatremia with encephalopathy (confusion)
requires hypertonic saline. The urine is maximally dilute (Uosm < 100) due to
suppressed ADH, but the free water load overwhelms excretion.
Q7. A 70-year-old with CHF (EF 25%) has Na 122, serum Osm 255, urine Osm 400,
urine Na 20. Edema, JVP 14 cm, crackles. What is the primary mechanism?
A) SIADH
B) Effective arterial volume depletion with non-osmotic ADH release
C) Primary polydipsia
D) Renal salt wasting
E) Hypothyroidism
Answer: B
Explanation: In heart failure, decreased effective arterial volume stimulates
baroreceptors, causing non-osmotic ADH release and water retention despite
hypervolemia. Urine Na is low due to reduced effective volume.
Q8. A 62-year-old with cirrhosis and ascites has Na 125, urine Osm 450, urine Na
12. What is the safest initial therapy for hyponatremia?
A) Vaptans
B) Fluid restriction
C) Hypertonic saline
D) Albumin infusion
E) Loop diuretics
Answer: B
Explanation: Fluid restriction is first-line for cirrhotic hyponatremia.
Vaptans are used with caution due to risk of rapid correction. Hypertonic
saline is reserved for severe symptoms.
3
, Q9. A patient with SIADH is treated with fluid restriction but Na drops from
125 to 120. What is the next best step?
A) Demeclocycline
B) Tolvaptan 15 mg daily
C) Hypertonic saline bolus
D) Increase fluid restriction to 500 mL
E) IV normal saline
Answer: B
Explanation: Tolvaptan is indicated for euvolemic/hypervolemic hyponatremia
resistant to fluid restriction. Demeclocycline is an alternative but has
nephrotoxicity. Hypertonic saline is for symptomatic hyponatremia.
Q10. A 48-year-old with traumatic brain injury has Na 130, urine Osm 780, urine
Na 120. What distinguishes SIADH from cerebral salt wasting (CSW)?
A) Serum uric acid
B) Urine output
C) BUN/Cr ratio
D) Response to normal saline
E) Serum potassium
Answer: D
Explanation: CSW improves with volume repletion (normal saline) and is a
hypovolemic state. SIADH worsens with saline (urine Na excretion increases)
and is euvolemic. Low uric acid and high FEurate occur in both.
Q11. A 55-year-old with schizophrenia polydipsia has Na 119, serum Osm 242,
urine Osm 50, urine Na 15. What is the mechanism?
A) ADH excess
B) Primary polydipsia with dilute urine
C) Reset osmostat
D) Renal failure
E) Diabetes insipidus
Answer: B
Explanation: Psychogenic polydipsia leads to massive free water intake,
suppressing ADH and producing maximally dilute urine (Uosm < 100).
Differentiate from nephrogenic DI by normal response to water deprivation.
Q12. A 67-year-old with pneumonia has Na 128, serum Osm 265, urine Osm 510,
4
