Hypernatremia
Question 1
A 14‑year‑old boy presents with confusion after three days of vomiting and poor oral intake.
BMP: Na 154 mEq/L, Cl 118mEq/L, HCO3 24mEq/L, Serum osmolality: 312 mOsm/kg, UA: SG 1.028, Urine osmolality 820 mOsm/kg
What is the most likely cause of his hypernatremia?
A. Central diabetes insipidus
B. Nephrogenic diabetes insipidus
C. Extrarenal free water loss
D. SIADH
E. Psychogenic polydipsia
Question 2
A 12‑year‑old child develops polyuria after head trauma.
BMP: Na 156mEq/L, Serum osmolality 310mOsm/kg, UA: SG 1.002, Urine osmolality 120mOsm/kg, Urine sodium 18mEq/L
What is the most likely diagnosis?
A. Central diabetes insipidus
B. Nephrogenic diabetes insipidus
C. Osmotic diuresis
D. Hypertonic saline infusion
E. Diuretic therapy
Question 3
A 13‑year‑old patient with bipolar disorder presents with severe thirst and polyuria.
BMP: Na 148mEq/L, Serum osmolality 305mOsm/kg, Urine osmolality 150mOsm/kg, SG 1.003
Which medication history would most strongly support the diagnosis?
A. Lithium therapy
B. Prednisone therapy
C. ACE inhibitor therapy
D. Amoxicillin therapy
E. Metformin therapy
Question 4
A hospitalized patient receiving 3% saline infusion develops hypernatremia.
BMP: Na 160mE/qL, Serum osmolality 325mOsm/kg, Urine osmolality 650mOsm/kg, SG 1.025, urine sodium 150mEq/L
Which mechanism best explains the hypernatremia?
A. Renal water loss
B. Sodium gain
C. Osmotic diuresis
D. Central DI
E. Nephrogenic DI
Question 5
A 10‑year‑old boy presents with polyuria and polydipsia.
BMP: Na 150mEq/L, Serum osmolality 308mOsm/kg, Urine osmolality 110mOsm/kg, SG 1.002. After desmopressin administration, urine osmolality rises to 720 mOsm/kg.
What is the diagnosis?
A. Nephrogenic DI
B. Hypertonic saline administration
C. Osmotic diuresis
D. Primary polydipsia
E. Central DI
Question 6
A patient has hypernatremia with the following labs:
Na 152mEq/L, Serum osmolality 310mOsm/kg, Urine osmolality 750mOsm/kg, Urine sodium 10mEq/L
What is the most likely cause of his laboratory findings?
A. Central DI
B. Nephrogenic DI
C. GI fluid loss
D. Osmotic diuresis
E. Renal tubular acidosis
Question 7
A patient receiving loop diuretics develops hypernatremia.
BMP: Na 150mEq/L, Urine osmolality 450mOsm/kg, Urine sodium 85mEq/L
Which mechanism best explains the hypernatremia?
A. Free water loss due to diuresis
B. Excess sodium administration
C. Central DI
D. Nephrogenic DI
E. Primary polydipsia
Question 8
A 16‑year‑old patient presents with hypernatremia and severe hyperglycemia.
BMP: Na 151mEq/L, Glucose 680mg/dL, Urine osmolality 700mOsm/kg, UA: Glucose 4+
Which mechanism explains the hypernatremia?
A. Central DI
B. Osmotic diuresis
C. Nephrogenic DI
D. SIADH
E. Salt intoxication
Question 9
A patient with hypernatremia has the following labs:
Na 158mEq/L, Serum osmolality 320mOsm/kg, Urine osmolality 90mOsm/kg, SG 1.001
Which disorder is most likely?
A. Extrarenal water loss
B. Hypertonic saline infusion
C. Osmotic diuresis
D. Central DI
E. Primary hyperaldosteronism
Question 10
A 12‑year‑old boy presents with polyuria and hypernatremia.
Urine osmolality 120mOsm/kg, After desmopressin urine osmolality increases to 140mOsm/kg.
What is the most likely diagnosis?
A. Central DI
B. Nephrogenic DI
C. Psychogenic polydipsia
D. Osmotic diuresis
E. SIADH
Question 11
A patient with central DI would most likely have which laboratory pattern?
A. High serum osmolality with concentrated urine
B. Low serum osmolality with dilute urine
C. High serum osmolality with dilute urine
D. Normal sodium with concentrated urine
E. Low sodium with dilute urine
Question 12
A patient with hypernatremia has serum osm 310mOsm/kg and urine osm 850mOsm/kg.
What does this indicate?
A. Appropriate renal response
B. Central DI
C. Nephrogenic DI
D. Osmotic diuresis
E. Psychogenic polydipsia
Question 13
A patient develops hypernatremia after severe diarrhea.
Urine osm 820mOsm/kg, Urine sodium 8mEq/L
Which mechanism explains this?
A. Renal water loss
B. GI water loss
C. Osmotic diuresis
D. Central DI
E. Hypertonic saline infusion
Question 14
A patient has hypernatremia with Na 149mEq/L and urine osm 350mOsm/kg.
What condition is suggested?
A. Partial DI
B. Extrarenal losses
C. Central DI
D. Nephrogenic DI
E. Salt intoxication
Question 15
A hospitalized patient unable to drink water develops hypernatremia.
Urine osm 900mOsm/kg.
What is the most likely cause?
A. Diabetes insipidus
B. Renal failure
C. Osmotic diuresis
D. Loop diuretics
E. Water deprivation
Question 16
Which urine finding most strongly suggests diabetes insipidus?
A. Urine osm >800
B. Urine osm <300
C. Urine sodium <10
D. Urine sodium >80
E. Urine glucose positive
Question 17
A patient receiving mannitol therapy develops hypernatremia.
Urine osmolality 650mOsm/kg, UA: no protein, no blood
Which mechanism explains the hypernatremia?
A. Central DI
B. GI loss
C. Nephrogenic DI
D. Osmotic diuresis
E. Salt intoxication
Question 18
A patient with nephrogenic DI would most likely have which pattern?
A. Hypernatremia with concentrated urine
B. Hypernatremia with dilute urine
C. Hyponatremia with dilute urine
D. Hyponatremia with concentrated urine
E. Normal sodium with concentrated urine
Question 19
Which urine electrolyte pattern suggests volume depletion from extrarenal losses?
A. Urine sodium >100
B. Urine sodium <20
C. Urine sodium 80
D. Urine sodium 120
E. Urine sodium 200
Question 20
Which test is most important in determining the cause of hypernatremia?
A. Urine osmolality
B. Urine sodium
C. Serum potassium
D. Urine protein
E. Serum bicarbonate
Answer Key
1. C . High urine osmolality (>800) indicates appropriate renal concentration. Hypernatremia therefore results from extrarenal water loss such as vomiting or dehydration.
2. A . Head trauma commonly causes central DI. Hypernatremia with dilute urine strongly supports impaired ADH secretion.
3. A . Lithium causes nephrogenic DI by impairing ADH response in the collecting duct.
4. B . Hypertonic saline produces hypernatremia via sodium gain rather than water loss.
5. E . Urine osmolality increasing dramatically after desmopressin confirms central DI.
6. C . Concentrated urine and low urine sodium indicate appropriate kidney response to volume depletion from GI losses.
7. A . Loop diuretics promote free water loss through increased urine output. urine osmolality is relatively low due to the water losses.
8. B. Severe hyperglycemia causes osmotic diuresis with water loss.
9. D. Very dilute urine in hypernatremia suggests diabetes insipidus.
10. B. Lack of significant response to desmopressin indicates nephrogenic DI.
11. C. Central DI causes high serum osmolality with inappropriately dilute urine.
12. A. Highly concentrated urine shows appropriate ADH response.
13. B. GI losses produce hypernatremia with concentrated urine and low urine sodium.
14. A. Intermediate urine osmolality suggests partial DI.
15. E. Hypernatremia with very concentrated urine indicates intact kidneys but insufficient water intake.
16. B. Urine osmolality <300 in hypernatremia suggests diabetes insipidus.
17. D. Mannitol causes osmotic diuresis leading to water loss.
18. B. Nephrogenic DI produces dilute urine despite hypernatremia.
19. B. Urine sodium <20 suggests extrarenal volume loss.
20. A. Urine osmolality is the key diagnostic test in evaluating hypernatremia.