Potassium

5 mL blood in lithium heparin or plain tube.

Rapid separation of plasma or serum from cells is essential (within 4 h).

Whole blood must never be stored or transported at < 10°C.

With marked leucocytosis and thrombocytosis, blood for potassium measurements should be specially handled by the laboratory. Plasma is required in these situations.

ISE or flame emission spectrophotometry.

See Table 6 for serum and plasma reference intervals.

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

Investigation of mineralocorticoid status.

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 can falsely increase potassium levels.

See Table 1.