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Low potassium (hypokalaemia)

Potassium is important for a person's muscles to work effectively, including the heart. Potassium also has a role in regulating blood pressure.

Low potassium levels (hypokalaemia) can cause weakness as cellular processes are affected.

Potassium is a mineral ( electrolyte) in the body. Almost 98% of potassium is found inside the cells. Small changes in the level of potassium that is present outside the cells can have severe effects on the heart, nerves and muscles.

The kidney is the main organ that controls the balance of potassium by removing excess potassium into the urine.

The normal potassium level is 3.5-5.0 mmol/L (millimoles per litre) Low potassium is defined as a potassium level below 3.5 mmol/L.

People with eating disorders such as anorexia nervosa and bulimia, patients with AIDS, alcoholics, and those who have had bariatric surgery have a higher incidence of hypokalaemia than others.

Low potassium causes

Dehydration, diarrhoea, excessive sweating (hyperhidrosis) and laxative abuse are common causes of low potassium levels.

It may also be caused by a lack of potassium in the diet; however, this is uncommon.

Other causes include medicines that affect the amount of potassium in the body, such as water pills.

Low potassium symptoms

Symptoms of low potassium are usually mild. At times the effects of low potassium can be vague. There may be more than one symptom involving the gastrointestinal (GI) tract, kidneys, muscles, heart and nerves.

  • Weakness, tiredness, or cramping in arm or leg muscles, sometimes severe enough to cause inability to move arms or legs due to weakness (much like a paralysis)
  • Tingling or numbness
  • Nausea or vomiting
  • Abdominal cramping, bloating
  • Constipation
  • Palpitations (feeling your heart beat irregularly)
  • Passing large amounts of urine or feeling very thirsty most of the time
  • Fainting due to low blood pressure
  • Abnormal psychological behaviour: depression, psychosis, delirium, confusion or hallucinations.

When to seek medical attention

If you are having symptoms of low potassium, seek medical advice. If you have muscle cramps, weakness, palpitations, or feel faint and you are taking a diuretic (water pill), seek urgent medical advice.

Without symptoms, you will not know you have low potassium levels until you have a routine blood test or an electrocardiogram (ECG).

Low potassium diagnosis

Sometimes the cause of low potassium is not clear. Your doctor may perform certain tests to rule out other conditions such as renal tubular acidosis, Cushing's syndrome, and hypocalcaemia.

Blood tests check potassium level, kidney function, glucose, magnesium, calcium and phosphorous if an electrolyte imbalance is suspected. Because low potassium is known to affect heart rhythms (arrhythmias), a doctor may order a digoxin level if you are taking a digitalis medicine.

ECG or a heart tracing is done to detect electrical changes in the heart and certain types of irregular heart rhythms that may be caused by low potassium.

WebMD Medical Reference

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