Hyponatraemia

Question 1

Urine Na+ and Urine osmolarity results in dehydration

Answer 1

• urine Na+ → low

(as kidney tries to compensate retaining sodium)

• urine osmolarity → high

Question 2

Urine Na+ and Urine osmolarity results in SIADH

Answer 2

• urine Na+ → high

(RASS will switch off due to fluid overload (below) → Na+ into urine)

• urine osmolarity → high

(as Na+ retained in the body)

Question 3

Urine Na+ and Urine osmolarity results in Heart Failure or Liver Cirrhosis

Answer 3

Organ failure e.g. HF → extravascular volume overload from transudate but intravascular volume depletion

• urine Na+ → low

(as body ‘dehydrated’ so RASS on and kidney keeps sodium in)

• urine osmolarity → high

Question 4

Urine Na+ and Urine osmolarity results in Diuretics

Answer 4

• urine Na+ → high

(body can’t retain Na+ due to diuretics)

• urine osmolarity → high

(ADH still on due to volume depletion)

Question 5

Urine Na+ and urine osmolarity in Polydypsia & Tea and Toast diet

Answer 5

• Urine Na+ → Low

(too much water and not enough sodium to pee out compared to water store)

• Urine osmolarity →Low

(as lots of water is pee out)