What is potassium?
Potassium is one of the primary electrolytes (crucial chemicals for cell function), and is concentrated within the cells of the body. Only 2% of the body's total potassium is available in the serum or blood stream. Small changes in the serum levels of potassium can affect body function. One of the more important functions of potassium is to maintain the electrical activity of the cells in the body. Cells with high electrical activity (for example, nerves and muscles, including the heart) are particularly affected when potassium levels fall.
Normal serum potassium levels range from 3.5 to 5.0 mEq/liter in the blood. Normal daily intake of potassium is 70-100 mEq (270 to 390 mg/dl), and requires the kidneys to remove that same amount each day. If more is removed, the body's total potassium store will be decreased, and the result is hypokalemia (hypo=low + kal=potassium +emia= in the blood) occurs.
Potassium enters the body through dietary intake. Examples of potassium rich foods include:
- Fresh fruits: bananas, cantaloupe, oranges, strawberries, kiwi, avocados, apricots
- Fresh vegetables: greens, mushrooms, peas, beets, tomatoes
- Meats: beef, fish, turkey,
- Juices: Orange, prune, apricot, grapefruit
What are the causes of low potassium (hypokalemia)?
Hypokalemia is not commonly caused by poor dietary intake.
The most common reason that potassium levels fall is due to the loss from the gastrointestinal (GI) tract and the kidney.
Potassium loss from the GI tract may be caused by:
- Ileostomy: In some patients who have had bowel surgery and have an ileostomy, the stool output can contain significant amounts of potassium.
- Villous adenoma (a type of colon polyp that can cause the colon to leak potassium)
- Laxative use
Causes of potassium loss from the kidney:
- Diuretic medications (water pills) like hydrochlorothiazide (HCTZ) or furosemide (Lasix)
- Elevated corticosteroid levels, either from medication like prednisone or from an illness like Cushing's Syndrome
- Elevated levels of aldosterone, a hormone that can increase with renal artery stenosis or adrenal tumors
- Renal tubular acidosis
- Low body magnesium levels
Low potassium levels may result from side effects of some medications:
- Aminoglycosides like gentamicin (Garamycin) or tobramycin (Nebcin)
- Amphotericin B
What are the symptoms of low potassium?
Potassium affects the way neuromuscular cells discharge energy (depolarize) and then regenerate (repolarize) that energy to be able to fire again. When potassium levels are low, the cells cannot repolarize and are unable to fire repeatedly, and muscles and nerves may not function normally. The effects of low potassium include may cause the following symptoms:
How is low potassium diagnosed?
Potassium levels in the blood may be easily measured by routine blood tests.
Low potassium is often a potential complication of medication. For example, patients with high blood pressure who are being treated with diuretics such as hydrochlorothiazide (Hydrodiuril) or furosemide (Lasix) often have their potassium levels monitored.
Patients who become ill with vomiting and diarrhea, may develop dehydration and weakness. Part of the patient evaluation may include having their electrolyte levels tested in order to determine whether body potassium losses may need to be replaced.
There can be electrocardiogram (EKG, ECG) changes associated with low potassium, and sometimes the diagnosis of low potassium is made incidentally by finding the characteristic "U" waves on the EKG tracing. In severe cases, hypokalemia can lead to dangerous disturbances in heart rhythm (dysrhythmia).
What is the treatment for low potassium?
Serum potassium levels above 3.0 mEq/liter are not considered dangerous or of great concern; they can be treated with potassium replacement by mouth. Depending on the patient's medical condition, other medical problems, and the patient's symptoms, serum levels lower than 3.0 mEq/liter may require intravenous replacement. Decisions are patient-specific and depend upon the diagnosis, the circumstances of the illness, and the patient's ability to tolerate fluid and medication by mouth.
Over the short-term, with self-limited illnesses like gastroenteritis with vomiting and diarrhea, the body is able to regulate and restore potassium levels on its own. However, if the hypokalemia is severe, or the losses of potassium are predicted to be ongoing, potassium replacement or supplementation may be required.
In those patients taking diuretics, often a small amount of oral potassium may be prescribed since the loss will continue as long as the medication is prescribed. Oral supplements may be in pill or liquid form, and the dosages are measured in mEq (milliequivalents). Common doses are 10-20mEq per day. Alternatively, consumption of foods high in potassium may be the first option in replacing potassium. Bananas, apricots, oranges, and tomatoes are high in potassium content. Since potassium is excreted in the kidney, blood tests that monitor kidney function may be ordered to predict and prevent potassium levels from rising too high.
When potassium needs to be given intravenously, it must be given slowly. Potassium is irritating to the vein and is usually administered at a maximal rate of 10 mEq per hour. Moreover, infusing potassium too quickly can cause heart irritation and promote potentially dangerous rhythms such as ventricular tachycardia.
A Special Situation: Periodic Paralysis
Rarely, a special situation will occur when all the potassium in the body shifts from the serum into the cells of the body. This drops the serum potassium levels to 1.0 mEq/liter or lower. This causes immediate muscle weakness to the point that the patient cannot move and becomes paralyzed. Arms and legs are most affected. Rarely, breathing and swallowing muscles can be involved.
Periodic paralysis may be hereditary and may be precipitated by excessive exercise, a high carbohydrate or high salt meal, or may occur without apparent cause.
Treatment by potassium replacement intravenously is effective, and recovery occurs within 24 hours.
How can low potassium be prevented?
The body is usually able to maintain potassium levels within the normal range as long as there is adequate potassium in the diet. When the body loses potassium due to a short-term illness, the body is able to compensate for the loss. When the potassium loss is be ongoing, it is important for the patient and health-care professional to anticipate the loss, and consider routine potassium replacement.
Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine
American Heart Association
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.