The measurement of sodium, potassium, or both electrolytes is usually requested in the assessment of renal function, to assist in the management of a patient that is unconscious or confused or a diabetic
patient with ketoacidosis, to assess and monitor states of dehydration (particularly an infant losing fluid), to monitor diuretic therapy and to assist in fluid replacement therapy.
What are the Normal ranges for sodium and potassium?
Sodium:
134–146 mmol/l (134–146 mEq/l)
Potassium:
Adults: 3.6–5.0 mmol/l (3.6–5.0 mEq/l)
Newborns: 4.0–5.9 mmol/l (4.0–5.9 mEq/l)
Values are highest immediately after birth
What are causes of increase in Sodium levels?
An elevated sodium level is known as hypernatraemia. It is nearly always due to dehydration with the rise in sodium (also chloride and urea) being due
to a concentrating effect. It is usually brought about by a reduction of body water content by fluid loss without compensatory reduction in sodium content, rather than a dietary overload, although excessive IV saline is a potential factor.
Typical causes of hypernatraemia are:
– Severe vomiting
– Prolonged diarrhoea
– Profuse sweating, fever
– Polyuria, as in diabetes
– Hyperaldosteroidism
– Cushing’s syndrome
– Inadequate water intake
– Accidental ingestion of sea water.
Note: A high sodium level must be reported as soon as possible. Severe hypernatraemia (sodium level that has reached 155 mmol/ is a serious finding .
What are causes of low sodium levels?
A low sodium level is known as hyponatraemia. It is a common finding than hypernatraemia. A greatly
reduced level (as low as 125 mmol/l) indicates a dangerous condition and must be reported as soon as possible.
A low sodium level may accompany any severe illness including viral and bacterial infections, malaria, heart attacks, heart failure, strokes, and tumours of the brain and lung.
Other causes of hyponatraemia
– Surgery or severe accident.
– Treatment with diuretics.
– Side effect of some drugs.
– When loss of salt and water (e.g. by vomiting,
diarrhoea or excessive sweating) is replaced by
water only.
– Loss of sodium in the urine as in severe renal impairment and salt-losing nephritis.
– Hypoadrenalism (Addison’s disease). In tropical countries hypoadrenalism can be caused by tuberculosis of the adrenal glands.
What are causes of high Potassium levels?
A raised potassium level is known as hyperkalaemia.
Levels above 6.5 mmol/l are particularly dangerous and must be reported immediately because fatal
disorders of heart rhythm can occur suddenly.
Typical causes of hyperkalaemia are:
– Excessive IV infusion, or increased ingestion of
potassium.
– Reduced renal excretion, renal failure with oliguria, anuria, acidosis.
– Addison’s disease.
– Hypoaldosteronaemia.
– Leakage of cellular potassium following: acute starvation, gross haemolysis, diabetic ketoacidosis, dehydration, severe tissue injury.
Falsely high potassium result: This can occur if a blood sample is haemolyzed due to poor venepuncture technique, a sample is left for a long time (e.g.
overnight) without the plasma or serum being removed or if whole blood is refrigerated before it is centrifuged. Red cells contain a high concentration
of potassium.
What are causes of low Potassium levels?
A low potassium level is called hypokalemia. The depletion of potassium can be masked by topping up of the plasma levels from intracellular sources and clinical symptoms may present in the
face of apparently normal values. These include:
weakness, tetany, polyuria and ECG changes.
Causes of hypokalaemia include:
– Inadequate intake of potassium in the diet and long term starvation.
– Increased loss of potassium due to prolonged vomiting or diarrhoea, renal tubular failure, diuretics, hyperaldosteroidism.
– Redistribution from plasma into cells; insulin therapy, metabolic or respiratory alkalosis.
Note: In the management of patients with salt and water depletion a simple test for urine chloride may be of value when facilities are not available for measuring serum or plasma electrolytes.
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