Sodium

Question 1

What are the biochemical findings in Addison’s disease?

Answer 1

High potassium, low sodium, normal osmolality.

Question 2

What is the clinical presentation of an Addisonian crisis?

Answer 2

Nausea and shock.

Question 3

What are the biochemical findings in Conn’s syndrome?

Answer 3

Low potassium, high sodium, hypertension.

Question 4

What is the primary cause of Conn’s syndrome?

Answer 4

Primary hyperaldosteronism.

Question 5

What are the biochemical findings in SIADH?

Answer 5

High urinary sodium,
high urine osmolality,
low plasma osmolality.

Question 6

What are the common causes of SIADH? (4)

Answer 6

Intracerebral

Alveolar

Drugs

Hormones

Question 7

How is SIADH managed? (3)

Answer 7

Fluid restriction

Demeclocycline

Tolvaptan

Question 8

What are the biochemical findings in psychogenic polydipsia? (4)

Answer 8

Low sodium
Low potassium
Low urine osmolality
Low plasma osmolality

Question 9

What is the key differentiation between psychogenic polydipsia and DI? (1)

Answer 9

Polydipsia: Low sodium, low K⁺

DI: High sodium, hypovolaemic

Question 10

What are the biochemical findings in DI? (3)

Answer 10

High sodium
Low urine osmolality
Hypovolaemia

Question 11

What is the difference between cranial and nephrogenic DI? (2)

Answer 11

Cranial DI: Urine concentrates after desmopressin → managed with replacement DDAVP

Nephrogenic DI: No change in urine after desmopressin → causes include genetics, drugs (e.g., lithium) → managed with thiazide diuretics

Question 12

What is the most common cause of sudden-onset DI? (1)

Answer 12

Pituitary metastases

Question 13

What is the investigation of choice for DI due to pituitary metastases? (1)

Answer 13

MRI

Question 14

What are the biochemical findings in HONK? (4) (Hyperosmolar Hyperglycaemic state)

Answer 14

Low potassium

High glucose

High serum osmolality (>320)

High bicarbonate (>15 mmol/L)

Question 15

How can diabetes mellitus affect sodium levels? (1)

Answer 15

High lipids create pseudohyponatraemia with normal osmolality

Question 16

What are the biochemical findings 3 days post-prostatectomy? (3)

Answer 16

Low sodium
Normal potassium
Normal volume

Question 17

What causes hyponatraemia post-prostatectomy? (1)

Answer 17

Fluid overload (plain water given in TURP)

Question 18

What are the biochemical findings in CAH? (4)

Answer 18

Hyponatraemia
Hyperkalaemia
Inadequate aldosterone synthesis
Hyperandrogenism

Question 19

What is the main driving force behind hyponatraemia?

Answer 19

Water problem! (Not a sodium issue), due to excess extracellular water

Question 20

What are the two stimulants of ADH secretion? (2)

Answer 20

High osmolality (detected by osmoreceptors in the hypothalamus).

Low blood pressure or blood volume (detected by baroreceptors in the aorta/atria/carotids).

Question 21

What is the only exception where hyponatraemia is not caused by ADH excess?

Answer 21

Psychogenic polydipsia.

Question 22

What is the maximum sodium correction rate per hour to prevent central pontine myelinolysis (CPM)?

Answer 22

No more than 8–10 mmol/L in the first 24 hours.

Question 23

What should you measure after diagnosing hyponatraemia to determine its type? (2)

Answer 23

Serum osmolality.

Urine osmolality.

Question 24

What are the signs of hyponatraemia? (3)

Answer 24

Confusion.

Seizures.

Reduced GCS.

Question 25

What are the signs of hypovolaemia? (3)

Answer 25

Reduced skin turgor.

Dry mucous membranes.

Postural hypotension.

Question 26

What is the most reliable marker of hypovolaemia?

Answer 26

Urine sodium concentration (< 20 mmol/L).

Question 27

How do you manage hypovolaemic hyponatraemia?

Answer 27

0.9% saline volume replacement.

Question 28

What are the causes of euvolaemic hyponatraemia? (2)

Answer 28

Hypothyroidism (check TFTs).

SIADH (serum and urine osmolality).

Question 29

How do you diagnose SIADH? (3)

Answer 29

Serum osmolality is low.

Urine sodium and osmolality are high.

Exclude hypothyroidism and adrenal insufficiency.

Question 30

What is the treatment for SIADH? (2)

Answer 30

Fluid restriction.

Additional drugs such as demeclocycline or tolvaptan (V2 receptor antagonist).

Question 31

What are the signs of hypervolaemia? (3)

Answer 31

Raised JVP.

Peripheral oedema.

Pulmonary oedema.

Question 32

What are two possible urine sodium levels and their causes in hypervolaemic hyponatraemia? (2)

Answer 32

Urine sodium > 20 mmol/L: renal causes (e.g., nephrotic syndrome, renal failure).

Urine sodium < 20 mmol/L: cardiac failure or cirrhosis.

Question 33

What is the treatment for hypervolaemic hyponatraemia?

Answer 33

Fluid restriction and treat the underlying cause.

Question 34

What is pseudohyponatraemia, and what causes it? (2)

Answer 34

Hyponatraemia with normal plasma osmolality.

Causes: Increased protein or lipids (e.g., multiple myeloma, diabetes mellitus).

Question 35

How do you manage severe hyponatraemia (e.g., coma, seizures)?

Answer 35

Hypertonic 3% saline.

Question 36

What is the primary cause of hypernatraemia?

Answer 36

Unreplaced water loss.

Question 37

What are the causes of hypernatraemia? (3)

Answer 37

GI losses (e.g., diarrhoea).

Sweat losses.

Renal losses (e.g., osmotic diuresis in diabetes mellitus, diabetes insipidus).

Question 38

What investigations help diagnose diabetes insipidus? (4)

Answer 38

Blood glucose (to rule out diabetes mellitus).

Plasma osmolality (high).

Urine osmolality (low).

Water deprivation test.

Question 39

How do you manage hypernatraemia? (2)

Answer 39

Correct water deficit with 5% dextrose.

Correct extracellular fluid volume with 0.9% saline.