Blood potassium levels are closely regulated since both high and low levels can have life-threatening consequences. A normal potassium blood level is typically 3.5 to 5 milliequivalents per liter, or mEq/L. The normal range may vary slightly among testing laboratories, however. Signs and symptoms of low blood potassium usually appear at levels of 3 mEq/L or less. The lower the potassium level, the more severe the symptoms tend to be. Signs and symptoms of a low blood potassium level primarily affect the heart, muscles, kidneys and digestive system.
Muscle-Related Signs and Symptoms
Potassium is required to maintain the chemical and electrical forces responsible for muscle movement. The most common symptoms of a low blood potassium level are fatigue and muscle weakness, which typically manifest as a decreased ability to perform physical work or exercise. Muscle tenderness, cramps and twitches are also common. With extremely low potassium levels, the muscles may lose the ability to contract, leading to paralysis. The legs and arms are typically affected before the trunk and chest. Widespread paralysis can disrupt the ability to breathe. In some cases, a very low potassium level has the opposite effect and the muscles spasm, cannot relax and eventually break down. Muscle proteins then leak into the bloodstream and can damage the kidneys.
Cardiovascular Signs and Symptoms
The heart is able to work tirelessly thanks to a fine balance of important chemicals -- such as potassium and sodium -- between the heart cells and the bloodstream. A low potassium level upsets this balance and can disrupt the regular rhythm of the heart. This is usually experienced as skipped, pounding, racing or irregular heartbeats, which can lead to chest pain, dizziness or fainting. In severe cases and especially among people with a pre-existing heart problem, the heart may stop. The blood pressure typically drops when the blood potassium level falls, particularly when arising to a standing position. High blood pressure can be seen in some cases, however.
Kidney-Related Signs and Symptoms
Healthy kidneys filter blood, removing impurities and returning useful substances to the bloodstream to maintain water and chemical balance. Low blood potassium levels typically cause excess water loss from the kidneys. Thus, people with a potassium deficiency usually urinate frequently and produce more urine than normal. The water loss triggers ongoing thirst and drinking more fluids to compensate. The kidneys may malfunction if a low potassium level persists without treatment, and people with pre-existing kidney disease are vulnerable to kidney failure.
Digestive Signs and Symptoms
The stomach and intestines contain muscle cells in their walls that propel food through the digestive system. A low potassium level makes these muscle cells sluggish, which can lead to a variety of symptoms. Constipation is most common, with infrequent and difficult-to-pass stools. With a severely low potassium level, the propelling movements of the intestines may stop entirely, causing nausea, vomiting, lack of appetite, bloating and abdominal pain.
When To Seek Medical Attention
A low blood potassium level can cause dangerous, potentially life-threatening complications. Seek medical attention without delay if you have signs or symptoms of a low blood potassium -- especially if you have existing heart or kidney disease. Potassium deficiency can be corrected, but hospitalization may be needed.