Urine Electrolytes
Urinary Sodium
Increased Urinary Sodium: Salt and water lost through kidneys
- HYPOnatremia with hypovolaemia
- Renal failure
- ATN
- Addison’s
- Osmotic diuresis (Raised glucose and urea)
- Diuretics (Thiazides)
- Cerebral salt wasting
- HYPOnatraemia with euvolaemia
- Elevated urine osmolality (SIADH)
- HYPOnatraemia with oedema
- Renal failure
- Hypertonic saline
Decreased Urinary Sodium: Increased interstitial salt attempted Na retention
- HYPOnatraemia with oedema
- Liver failure
- Cirrhosis
- CCF
- Nephrotic syndrome
- HYPOnatremia with dehydration (increased urine osmolality)
- Burns, fistula, heat illness
- Diarrhoea, sweat, vomiting
Urinary anion gap (UAG)
- Differentiate renal or GIT cause of HYPERchloraemic metabolic disorders
- or Normal anion gap metabolic acidosis (NAGMA)
Nature
- Urine must maintain electrical neutrality
- Urinary anion gap provides rough measure of urinary sodium excretion (Positively charged cation)
- Low anion gap associated with increased NH4+ excretion
Urinary AG = (UA – UC) = [Na+] + [K+] – [Cl]
Hyperchloraemic metabolic acidosis associated with
- neGUTive UAG
- Loss of base by GIT (Diarrohea)
- → hypovolemia and metabolic acidosis
- → ↑ NH4+ excretion
- → appropriate urine ↓Na but ‘inappropriate’ urine ↑Cl
- Loss of base by GIT (Diarrohea)
- POSITIVE UAG
- Loss of base by the kidney (RTA)
- Impaired renal acidification and kidney unable to excrete enough NH4+
- NOTE: However in the case of ‘gastric loss‘ the UAG is usually Positive
- → hypovolemia and metabolic acidosis
- → HCO3- excretion
- → ‘inappropriate’ urine ↑Na but appropriate urine ↓Cl
References and Links
- Unusual urine – Clinical Cases
- CCC – Urinalysis
- CCC – Urine electrolytes – Urinary anion gap
- Urinalysis Overview Table
Cite this article as: Mike Cadogan, "Urine Electrolytes," In: LITFL - Life in the FastLane, Accessed on March 20, 2023, https://litfl.com/urine-electrolytes/.
Critical Care
Compendium
Associate Professor Curtin Medical School, Curtin University. Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM Sir Charles Gairdner Hospital. Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |