Low potassium (hypokalemia) refers to a lower than normal potassium level in your bloodstream. Potassium helps carry electrical signals to cells in your body. It is critical to the proper functioning of nerve and muscles cells, particularly heart muscle cells.

Normally, your blood potassium level is 3.6 to 5.2 millimoles per liter (mmol/L). A very low potassium level (less than 2.5 mmol/L) can be life-threatening and requires urgent medical attention.

Low potassium (hypokalemia) has many causes. The most common cause is excessive potassium loss in urine due to prescription medications that increase urination. Also known as water pills or diuretics, these types of medications are often prescribed for people who have high blood pressure or heart disease.

Vomiting, diarrhea or both also can result in excessive potassium loss from the digestive tract. Occasionally, low potassium is caused by not getting enough potassium in your diet.

Causes of potassium loss include:

• Alcohol use (excessive)
• Chronic kidney disease
• Diabetic ketoacidosis (in which the body has high levels of blood acids called ketones)
• Diarrhea
• Diuretics (water retention relievers)
• Excessive laxative use
• Excessive sweating
• Folic acid deficiency
• Primary aldosteronism
• Some antibiotic use
• Vomiting

In most cases, low potassium is found by a blood test that is done because of an illness, or because you are taking diuretics. It is rare for low potassium to cause isolated symptoms such as muscle cramps if you are feeling well in other respects.

Low potassium symptoms may include:

• Weakness
• Fatigue
• Muscle cramps
• Constipation

Abnormal heart rhythms (arrhythmias) are the most worrisome complication of very low potassium levels, particularly in people with underlying heart disease.

Talk to your doctor about what your blood test results mean. You may need to change a medication that's affecting your potassium level, or you may need to treat another medical condition that's causing your low potassium level.

Treatment of low potassium is directed at the underlying cause and may include potassium supplements. Don't start taking potassium supplements without talking to your doctor first.