Urinary Electrolytes

OVERVIEW

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

USES

Oliguria

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

Hyponatraemia

• 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

Hypokalaemia

• 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

• Urine Color
• Urine Transparency (turbidity)
• Dipstick urinalysis
• CCC – Urinalysis
• Laboratory Urinalysis
• Urinalysis Overview Table
• Urine electrolytes – Urinary anion gap