Specimen requirement

Plasma

Urine

Fluid

Adult patient:

 Heparin gel tube

Minimum blood volume: 5 mL

Spot urine:

Plain bottle

Minimum volume: 10 mL

24 Hr urine:

U1 bottle / U2 bottle

Spot fluid:

Plain bottle

Minimum volume: 10 mL

Paediatric patient:

Paediatric heparin tube

Number of vials: 1

Minimum blood volume: 1.3 mL

Authorisation code required

No

No

No

24 Hr available service

Yes

(Call extension: 3353 for express result)

Spot urine: Yes

24 Hr urine: No

No

Precaution

Avoid haemolysis during blood taking.

Avoid prolonged contact of the sample with red cells which will cause elevated potassium.

Blood samples should not be stored or transported at < 10 °C.

With marked leucocytosis and thrombocytosis, blood for potassium measurements should be specially handled by the laboratory.

Method

Ion selective electrode

Reference interval

Plasma:

(Source:

1. The reference range is quoted from Robert WL et al. Reference Information for the Clinical Laboratory. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 4th Edn. Burtis CA, Ashwood ER, Bruns DE eds. Elsevier Saunders 2006
    

2. Genuine hyperkalaemia is defined as plasma K > 5.0 mmol/L. Risk of hyperkalaemia increases with decreasing renal function. Arch Intern Med 2009; 169(17): 1587 - 94
    

3. The above operational reference range included the lower limit of the reference range determined for the normal healthy population mentioned above and the upper limit of 5.0 mmol/L corresponding to the international definition of genuine hyperkalaemia. This operational range was endorsed by the Cluster Ops Meeting on 26 May 2011 for the operational needs of NTEC.)

24 Hr urine: 25 - 125 mmol/d

The urinary excretion of potassium varies significantly with dietary intake. The values given are typical of subjects on average diet.

(Source: from manufacturer’s kit insert)

Clinical indication

Plasma:

1. Monitoring potassium status in patients on diuretics or on intravenous therapy, and in those with renal disease, acid-base disturbances or gastrointestinal tract fluid losses.
    

2. Investigation of mineralocorticoid status

Urine:

1. Differentiation of renal potassium loss from other causes of hypokalaemia.

Result interpretation

Plasma:

Increased levels are usually found in acidosis, tissue damage, renal failure and mineralo­corticoid deficiency.

Decreased levels are found in association with loop or thiazide diuretic therapy, vomiting or diarrhoea, alkalosis, during treatment of acidosis, and with mineralocorticoid excess.

Haemolysis during collection, delay in separation, refrigeration of unseparated blood, marked leucocytosis and thrombocytosis, and muscle activity of limb immediately prior to venepuncture may cause a misleading increase in potassium.

Urine:

Urine potassium is only useful when performed at the same time with a plasma postassium.

Mineralocorticoid excess, some renal tubular disorders, metabolic alkalosis, some diuretics and Bartter’s syndrome cause renal potassium loss. In primary hyperaldosteronism, the urine K is usually > 40 mmol/L when the plasma K is < 3.5 mmol/L.

With decreased intake or increased gastrointestinal loss, renal potassium loss is decreased.

Measurement of uncertainty

See table.

Frequency of measurement

Daily