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
• 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

CCC Differential Diagnosis Series
NEURO	Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision
RESP	Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
CVS	Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction
GIT	Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage
GUT	Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
MSK	Arthritis, Shoulder pain, Wasting of the small muscles of the hand
DERM	Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
ENDO	Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
HAEM	Splenomegaly
PAEDS	Floppy infant
MISC	Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
IMAGING	CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR, ABDO: Gas on abdominal X-ray, Kidney mass, BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly, OTHER: Pseudofracture on X-Ray,
LABS	LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia,  HIGH: Bilirubin and Jaundice, Hyperammonaemia, Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia,  ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis, Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes

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