Urinary Electrolytes


Urinary Electrolytes: used in the diagnosis of a number of electrolyte disturbances in ICU (especially when intake of electrolytes is known and relatively controlled)



  • UNa+ low (<10mmol/L) – extravascular volume depletion
  • UNa+ high (>20) – tubular damage


  • UNa+ low (<10) – extra-renal losses
  • UNa+ high (>20) – renal salt losing states, SIADH, diuretic therapy
  • Fractional excretion of Na+ = 100 x UNa+ x PCr / PNa+ x UCr
    -> < 1% implies pre-renal cause, limited by Na+ intake and diuretics therapy


  • UK+ high (>20) – renal loss of K+
  • UK+ low (<20) – extrarenal loss of K+

Normal Anion Gap Acidosis

  • UCl- can be used
  • UCl- low (<10) – RTA from impaired urinary acidification (decreased ammonium excretion)
    -> also present = positive urinary anion gap and an inappropriately high pH (>6)
  • if acidosis is due to an extra-renal loss of bicarbonate, in the absence of renal failure the kidneys will excrete ammonium and chloride
    -> negative urinary anion gap (UCl > Na + K)

References and Links

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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