Potassium (urine)

Specimen

24h urine

Units

mmol/24h

Reference Range

25 – 125 mmol/24 h

Test Usage

In healthy individuals, nearly all potassium filtered by the kidney is reabsorbed. Potassium excretion reflects distal tubule secretion of potassium, which is stimulated by aldosterone and the rate of potassium entry into the plasma from the diet and from cells. Urine potassium levels are generally helpful only in evaluation of patients with unexplained hypokalemia. Urine potassium levels between 0 and 10 mmol/L suggest the GI tract is the source of potassium loss, while levels >10 mmo/L suggest renal potassium loss.

The daily output depends on dietary intake but is commonly about 60-80 mmol/day. When there is hypokalaemia, normal renal and adrenal function will reduce output to <30 mmol/day after 2-3 days.

A higher value is consistent with adrenocortical excess (e.g. Conn’s syndrome), vomiting or diuretic therapy. With hyperkalaemia, normal homeostatic mechanisms should raise output to >130 mmol/day.

Turnaround time

1 day

Availability

Local test

Can be added on to an existing request up to 4 days following sample receipt