Question 1

A 7-year-old boy is admitted with pneumonia and poor oral intake. He is euvolemic on examination. BMP: Na 124 mEq/L, K 3.8 mEq/L, Cl 92 mEq/L, HCO3 24 mEq/L, BUN 8 mg/dL, creatinine 0.4 mg/dL, glucose 92 mg/dL. Serum osmolality is 264 mOsm/kg. UA: specific gravity 1.020, no blood, no protein, no glucose, no ketones. Urine osmolality is 520 mOsm/kg and urine sodium is 58 mEq/L. Which diagnosis is most likely?
 

A. SIADH

B. Primary polydipsia

C. Nephrotic syndrome

D. Pseudohyponatremia

E. Cerebral salt wasting
 

Question 2

A 12-year-old girl with severe hypertriglyceridemia is found to have sodium 127 mEq/L on a chemistry analyzer. BMP: K 4.1 mEq/L, Cl 98 mEq/L, HCO3 25 mEq/L, BUN 12 mg/dL, creatinine 0.6 mg/dL, glucose 96 mg/dL. Measured serum osmolality is 288 mOsm/kg. A blood gas sodium is 136 mEq/L. What is the best explanation?
 

A. True hypotonic hyponatremia

B. SIADH

C. Pseudohyponatremia

D. Hypovolemic hyponatremia

E. Reset osmostat

Question 3

A 9-year-old boy with new-onset diabetes presents with vomiting. BMP: Na 126 mEq/L, K 5.2 mEq/L, Cl 91 mEq/L, HCO3 12 mEq/L, BUN 18 mg/dL, creatinine 0.8 mg/dL, glucose 720 mg/dL. Serum osmolality is 308 mOsm/kg. UA: glucose 4+, ketones 3+, specific gravity 1.030. Which explanation best accounts for the low sodium?
 

A. SIADH

B. Primary polydipsia

C. Pseudohyponatremia from hyperproteinemia

D. Renal salt wasting

E.  Hyperglycemia-related translocational hyponatremia

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Question 4

A 6-year-old child with gastroenteritis presents with dry mucous membranes and tachycardia. BMP: Na 128 mEq/L, K 3.3 mEq/L, Cl 95 mEq/L, HCO3 18 mEq/L, BUN 22 mg/dL, creatinine 0.6 mg/dL, glucose 90 mg/dL. Serum osmolality is 270 mOsm/kg. UA: specific gravity 1.028, trace ketones, no protein, no blood. Urine sodium is 12 mEq/L and urine osmolality is 640 mOsm/kg. Which diagnosis is most likely?
 

A. SIADH

B. Hypovolemic hyponatremia from extrarenal salt and water loss

C. Pseudohyponatremia

D. Primary adrenal insufficiency

E. Nephrotic syndrome
 

Question 5

A 15-year-old boy with edema from nephrotic syndrome presents with hyponatremia. BMP: Na 126 mEq/L, K 4.2 mEq/L, Cl 96 mEq/L, HCO3 24 mEq/L, BUN 14 mg/dL, creatinine 0.7 mg/dL, albumin 1.8 g/dL. Serum osmolality is 268 mOsm/kg. UA: protein 4+, blood negative, glucose negative, specific gravity 1.026. What is the most likely mechanism of hyponatremia?
 

A. Primary polydipsia

B. Hypervolemic hyponatremia from low effective arterial blood volume

C. Pseudohyponatremia

D. Central diabetes insipidus

E. Distal RTA
 

Question 6

A 10-year-old child with seizures is found to have sodium 116 mEq/L. BMP: K 3.9 mEq/L, Cl 86 mEq/L, HCO3 23 mEq/L, BUN 7 mg/dL, creatinine 0.4 mg/dL, glucose 88 mg/dL. Serum osmolality is 252 mOsm/kg. Which immediate treatment is most appropriate?
 

A. 3% saline 3–5 mL/kg IV bolus

B. Fluid restriction only

C. 0.45% saline infusion

D. 0.9% NS at 1.5 times maintenance

E. Oral salt tablets only

Question 7

A 13-year-old girl on chronic thiazide therapy for hypertension presents with dizziness. BMP: Na 123 mEq/L, K 2.9 mEq/L, Cl 87 mEq/L, HCO3 28 mEq/L, BUN 16 mg/dL, creatinine 0.7 mg/dL, glucose 94 mg/dL. Serum osmolality is 262 mOsm/kg. UA: specific gravity 1.018, no protein, no blood. Urine sodium is 52 mEq/L and urine osmolality is 500 mOsm/kg. Which diagnosis is most likely?
 

A. SIADH

B. Primary polydipsia

C. Pseudohyponatremia

D. Diuretic-associated hyponatremia

E. Congenital Nephrogenic DI

Question 8

A 4-year-old girl drinks large volumes of water all day. She appears euvolemic. BMP: Na 129 mEq/L, K 3.7 mEq/L, Cl 98 mEq/L, HCO3 24 mEq/L, BUN 5 mg/dL, creatinine 0.3 mg/dL, glucose 85 mg/dL. Serum osmolality is 268 mOsm/kg. UA: specific gravity 1.001, no protein, no blood, no glucose. Urine osmolality is 65 mOsm/kg and urine sodium is 8 mEq/L. What is the most likely diagnosis?
 

A. SIADH

B. Pseudohyponatremia 

C. Nephrotic syndrome

D. Cerebral salt wasting

E. Primary polydipsia

Question 9

A 14-year-old boy after neurosurgery develops hyponatremia with high urine output and signs of volume depletion. BMP: Na 124 mEq/L, K 3.5 mEq/L, Cl 93 mEq/L, HCO3 22 mEq/L, BUN 18 mg/dL, creatinine 0.6 mg/dL, glucose 102 mg/dL. Serum osmolality is 262 mOsm/kg. Urine osmolality is 520 mOsm/kg and urine sodium is 120 mEq/L. Which diagnosis is most likely?
 

A. SIADH

B. Primary polydipsia

C. Pseudohyponatremia

D. Cerebral salt wasting

E. Central DI

Question 10

A 16-year-old girl is admitted for pain crisis from sickle cell disease and receives large volumes of hypotonic IV fluids. BMP: Na 125 mEq/L, K 4.0 mEq/L, Cl 94 mEq/L, HCO3 23 mEq/L, BUN 6 mg/dL, creatinine 0.5 mg/dL, glucose 90 mg/dL. Serum osmolality is 260 mOsm/kg. UA: specific gravity 1.012. Which etiology best explains her hyponatremia?
 

A. Iatrogenic hypotonic fluid administration

B. Pseudohyponatremia

C. Central DI

D. Primary polydipsia

E. Distal RTA

Question 11

A 9-year-old child with bronchiolitis is euvolemic and hyponatremic. BMP: Na 121 mEq/L, K 4.2 mEq/L, Cl 90 mEq/L, HCO3 24 mEq/L, BUN 9 mg/dL, creatinine 0.4 mg/dL, glucose 91 mg/dL. Serum osmolality 258 mOsm/kg, urine osmolality 460 mOsm/kg, urine sodium 46 mEq/L. Which treatment is most appropriate after acute symptoms are excluded?
 

A. D5W infusion

B. Fluid restriction and treatment of underlying cause

C. Free water bolus

D. Desmopressin

E. Loop diuretic plus hypotonic fluids

Question 12

A 7-year-old boy with nephrotic syndrome has worsening edema and sodium 124 mEq/L. He is not seizing and is hemodynamically stable. BMP: K 4.3 mEq/L, Cl 95 mEq/L, HCO3 24 mEq/L, BUN 15 mg/dL, creatinine 0.5 mg/dL, albumin 1.6 g/dL. UA: protein 4+, blood negative, SG 1.025. Which treatment strategy is most appropriate?
 

A. Large free water intake

B. Desmopressin

C. Fluid and sodium restriction with loop diuretic; consider albumin plus loop diuretic if intravascularly depleted

D. 3% saline as routine first-line therapy

E. Thiazide diuretic

Question 13

A 12-year-old girl with a small cell tumor and nausea is found to have euvolemic hyponatremia. BMP: Na 122 mEq/L, K 4.1 mEq/L, Cl 89 mEq/L, HCO3 25 mEq/L, BUN 7 mg/dL, creatinine 0.5 mg/dL, glucose 90 mg/dL. Serum osmolality is 256 mOsm/kg, urine osmolality 540 mOsm/kg, urine sodium 64 mEq/L. Which urine finding is inappropriately high for this sodium level and supports SIADH?
 

A. Urine sodium 8 mEq/L

B. Urine osmolality 540 mOsm/kg

C. Specific gravity 1.001

D. Urine ketones 3+

E. Urine glucose 4+

Question 14

A 5-year-old child with severe pneumonia presents with sodium 118 mEq/L and irritability but no seizures. BMP: K 3.9 mEq/L, Cl 87 mEq/L, HCO3 22 mEq/L, BUN 8 mg/dL, creatinine 0.3 mg/dL, glucose 92 mg/dL. Serum osmolality 250 mOsm/kg. Which correction limit is most appropriate if this is chronic hyponatremia?
 

A. Increase sodium by no more than 6 mEq/L in 24 hours

B. Increase sodium by 19 mEq/L in 24 hours

C. Increase sodium by no more than 15 mEq/L in 24 hours

D. Normalize sodium within 6 hours to avoid seizures

E. No correction is needed
 

Question 15

A 14-year-old with obesity has sodium 128 mEq/L on a chemistry panel. BMP: K 4.0 mEq/L, Cl 97 mEq/L, HCO3 24 mEq/L, BUN 11 mg/dL, creatinine 0.7 mg/dL, glucose 95 mg/dL. Measured serum osmolality is 289 mOsm/kg. Total protein is markedly elevated from IVIG therapy. Which diagnosis is most likely?
 

A. True hypotonic hyponatremia

B. Pseudohyponatremia from hyperproteinemia

C. SIADH

D. Primary polydipsia

E. Cerebral salt wasting

Question 16

A 3-year-old child drinks only water for two days because of poor feeding from a viral illness and receives no solute-containing fluids. BMP: Na 130 mEq/L, K 3.6 mEq/L, Cl 99 mEq/L, HCO3 23 mEq/L, BUN 4 mg/dL, creatinine 0.2 mg/dL, glucose 84 mg/dL. Serum osmolality is 270 mOsm/kg. Urine osmolality is 80 mOsm/kg. Which differential is most likely?
 

A. Nephrotic syndrome

B. SIADH

C. Low-solute intake / excess free water intake

D. Hyperglycemia

E. Pseudohyponatremia

Question 17

A 13-year-old girl with adrenal insufficiency presents with fatigue and vomiting. BMP: Na 122 mEq/L, K 5.8 mEq/L, Cl 92 mEq/L, HCO3 20 mEq/L, BUN 16 mg/dL, creatinine 0.7 mg/dL, glucose 72 mg/dL. Serum osmolality is 260 mOsm/kg. Urine sodium is 58 mEq/L and urine osmolality is 430 mOsm/kg. Which diagnosis is most likely?
 

A. Primary adrenal insufficiency causing hyponatremia

B. SIADH

C. Pseudohyponatremia

D. Primary polydipsia

E. Iatrogenic saline overload

Question 18

A 15-year-old boy with known SIADH from meningitis is being monitored on therapy. His sodium has improved from 119 mEq/L to 124 mEq/L over 24 hours. He is alert and euvolemic. Which management is most appropriate now?
 

A. Continue careful fluid restriction and monitor sodium

B. Give D5W to lower sodium again

C. Stop all monitoring because sodium is improving

D. Rapidly normalize sodium with repeated 3% saline boluses

E. Start desmopressin for long-term therapy of SIADH

Question 19

A 10-year-old child with hyponatremia has the following studies: sodium 123 mEq/L, serum osmolality 258 mOsm/kg, urine osmolality 510 mOsm/kg, urine sodium 48 mEq/L. She is euvolemic with no edema. UA: SG 1.020, protein negative, blood negative. Which diagnosis is most likely?
 

A. Pseudohyponatremia

B. Nephrotic syndrome

C. Primary polydipsia

D. SIADH

E. Hyperglycemia-related hyponatremia

Question 20

A 6-year-old boy with vomiting develops sodium 126 mEq/L and mild hypovolemia. BMP: K 3.2 mEq/L, Cl 92 mEq/L, HCO3 19 mEq/L, BUN 20 mg/dL, creatinine 0.5 mg/dL, glucose 88 mg/dL. Urine sodium is 10 mEq/L and urine osmolality is 610 mOsm/kg. Which treatment is most appropriate?
 

A. Fluid restriction alone

B. Isotonic fluid resuscitation and treatment of the underlying GI losses

C. 3% saline bolus regardless of symptoms

D. D5W infusion

E. Desmopressin

 

 

Answer Key 

1. A. Hypotonic hyponatremia with euvolemia, urine osmolality >100 mOsm/kg, and urine sodium >20–40 mEq/L fits SIADH. 

2. C . Pseudohyponatremia occurs when indirect sodium measurement is artifactually low because of hyperlipidemia or hyperproteinemia; a directly measured blood gas sodium may be normal. 

3. E . Hyperglycemia raises effective osmolality and draws water extracellularly, lowering the measured sodium. 

4. B . Hypovolemic hyponatremia from extrarenal losses causes concentrated urine and low urine sodium as the kidney conserves sodium.

5.  B. Nephrotic syndrome causes hypervolemic hyponatremia from reduced effective arterial blood volume with water retention.

6. A. Symptomatic severe hyponatremia requires hypertonic saline;  3% saline 3–5 mL/kg IV bolus will raise the serum sodium ~ 3-5mEq/L. 

7. D. Thiazides impair urinary dilution and commonly cause hyponatremia, often with hypokalemia and concentrated urine. 

8. E. Primary polydipsia causes hypotonic hyponatremia with maximally dilute urine. 

9. D. Cerebral salt wasting is suggested by CNS disease, hypovolemia, high urine output, elevated serum osmolality, and very high urine sodium.
 

10. A. Hospital-acquired hyponatremia is commonly caused by hypotonic IV fluids, especially when ADH is stimulated by pain or illness. 
 

11. B . Chronic or less symptomatic SIADH is typically treated with fluid restriction plus treatment of the underlying cause.
 

12. C. Nephrotic syndrome is generally treated with sodium/fluid restriction and loop diuretics; albumin plus loop diuretic may help when intravascular depletion limits diuresis. 
 

13. B. In SIADH, the urine remains inappropriately concentrated despite hyponatremia; urine osmolality >100 mOsm/kg supports ongoing ADH effect.
 

14. A. The max correction rate is 6-8 mEq/L in 24 hours for chronic hyponatremia.
 

15. B . Hyperproteinemia, including after IVIG, can cause pseudohyponatremia when sodium is measured indirectly after dilution. 

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16. C. Low-solute intake or excess free water intake produces hyponatremia with appropriately dilute urine. 
 

17.  A. Adrenal insufficiency can cause hyponatremia with hyperkalemia, hypotonic serum, concentrated urine, and inappropriately high urine sodium. 

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18. A. Gradual improvement within correction limits favors continued fluid restriction and serial sodium checks.

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19. D. Euvolemic hypotonic hyponatremia with urine osmolality >100 mOsm/kg and urine sodium >20–40 mEq/L strongly supports SIADH. 

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20. B . Hypovolemic hyponatremia from GI losses is treated with isotonic fluid resuscitation and correction of the underlying cause.