Specimen Name Result Units Range
Plasma Sodium 128 mmol/L (135-145)
Potassium 2.1 mmol/L (3.5-5.5)
Chloride 79 mmol/L (100-109)
Anion Gap 40 mmol/L (7-17)
Glucose 10.5 mmol/L (3.8-5.5)
Urea 3.0 mmol/L (2.7-7.2)
Creatinine 100 μmol/L (60-110)
Osmolality 272 mmol/kg (275-295)
Urine Sodium 6 mmol/L (> 20)
Osmolality 650 mmol/kg

Post-operative elective surgical patient.

No other history available.
Iatrogenic Water Overload - IVT with D5W

Hypo-osmolar hyponatraemia aetiology:

  1. Sodium loss (> water) - hypovolaemic
  2. Water excess - hypervolaemia (± oedema)
    • Excess hypotonic fluids - low-normal urea, hypotonic urine
    • CCF - high urea, hypertonic urine / low Na+
    • Nephrotic syndrome - high urea, isotonic urine
    • Cirrhosis - low urea
    • SIADH

 

However, also hypokalaemic metabolic alkalosis with high urine osmolality:

  • ? contraction alkalosis (e.g. vomiting) but urea is normal
  • ? pre-existing hypokalaemic alkalosis 2° diuretics etc.
  • ? element of SIADH, but urine [Na+] is too low