Diseases & Conditions
Most of the body's potassium is located inside the cells. Potassium is necessary for the normal functioning of cells, nerves, and muscles.
The body must maintain the potassium level in blood within a narrow range. A potassium level that is too high or too low can have serious consequences, such as an abnormal heart rhythm or even stopping of the heart (cardiac arrest). The body can use the potassium stored within cells to help maintain a constant level of potassium in blood.
The body maintains the right level of potassium by matching the amount of potassium consumed with the amount lost. Potassium is consumed in food and drinks that contain electrolytes (including potassium) and lost primarily in urine. Some potassium is also lost through the digestive tract and in sweat. Healthy kidneys can adjust the excretion of potassium to match changes in consumption.
Some drugs and certain conditions affect the movement of potassium into and out of cells, which greatly influences the potassium level in blood.
In hypokalemia, the level of potassium in blood is too low. A low potassium level has many causes but usually results from vomiting, diarrhea, adrenal gland disorders, or use of diuretics. A low potassium level can make muscles feel weak, cramp, twitch, or even become paralyzed, and abnormal heart rhythms may develop. The diagnosis is based on blood tests to measure the potassium level. Usually, eating foods rich in potassium or taking potassium supplements by mouth is all that is needed.
Typically, the potassium level becomes low because too much is lost from the digestive tract. Sometimes too much potassium is excreted in urine, usually because of diuretics that cause the kidneys to excrete excess sodium, water, and potassium. In many adrenal disorders, such as Cushing's syndrome (see Adrenal Gland Disorders: Cushing's Syndrome ), the adrenal glands produce too much aldosterone, a hormone that causes the kidneys to excrete large amounts of potassium.
Certain drugs cause more potassium to move from blood into cells and can result in hypokalemia. However, these drugs usually cause temporary hypokalemia, unless another condition is also causing potassium to be lost.
Hypokalemia is rarely caused by consuming too little because many foods contain potassium.
What Makes the Potassium Level Decrease?
Drugs or Other Circumstances
Increased loss from the digestive tract (most common)
Laxatives if used a long time
Increased excretion in urine
Aldosteronism due to a tumor in the adrenal glands
A low level of magnesium (hypomagnesemia)
Licorice (natural), if consumed in large amounts
Tobacco chewing (certain types)
Increased movement from blood into cells
An overactive thyroid gland (hyperthyroidism)
Insulin Some Trade Names HUMULIN NOVOLIN
Some drugs used to treat asthma: albuterol Some Trade Names PROVENTIL VENTOLIN , terbutaline Some Trade Names BRETHINE BRICANYL , and theophylline Some Trade Names BRONKODYL THEOLAIR
Symptoms and Diagnosis
A slight decrease in the potassium level in blood usually causes no symptoms. A larger decrease can cause muscle weakness, cramping, twitches, and even paralysis. Abnormal heart rhythms may develop. They may develop even when the decrease is slight if people already have a heart disorder or take the heart drug digoxin Some Trade Names LANOXIN .
The diagnosis is made by measuring the potassium level in the blood. Doctors then try to identify what is causing the decrease. The cause may be clear based on the person's symptoms (such as vomiting) or use of drugs or other substances. If the cause is not clear, doctors measure how much potassium is excreted in urine to determine whether excess excretion is the cause.
If a disorder is causing hypokalemia, it is treated.
Usually, potassium can be replaced by eating potassium-rich foods or by taking potassium supplements by mouth. Because potassium can irritate the digestive tract, supplements should be taken in small doses with food several times a day rather than in a single large dose. Special types of potassium supplements, such as wax-impregnated or microencapsulated potassium chloride, are much less likely to irritate the digestive tract.
Potassium is given intravenously in the following situations: The potassium level is dangerously low. Supplements taken by mouth are ineffective. People continue to lose too much potassium to be replaced using supplements taken by mouth. The low level causes abnormal heart rhythms.
Most people who take diuretics do not need to take potassium supplements. Nevertheless, doctors periodically check the potassium level in blood so that the drug regimen can be changed if necessary. Alternatively, diuretics that help the kidneys conserve potassium (potassium-sparing diuretics), such as amiloride Some Trade Names MIDAMOR , eplerenone, spironolactone Some Trade Names ALDACTONE , or triamterene Some Trade Names DYRENIUM ) can be used, but only if the kidneys are functioning normally.
In hyperkalemia, the level of potassium in blood is too high. A high potassium level has many causes, including kidney disorders, drugs that affect kidney function, and consumption of too much supplemental potassium. Usually, hyperkalemia must be severe before it causes symptoms, mainly abnormal heart rhythms. Doctors usually detect hyperkalemia when blood tests or electrocardiography is done for other reasons. Treatment includes reducing consumption of potassium, stopping drugs that may cause hyperkalemia, and using drugs to increase potassium excretion.
Usually, hyperkalemia results from several simultaneous problems, including the following: Kidney disorders (such as kidney failure) that prevent the kidneys from excreting enough potassium Drugs that prevent the kidneys from excreting normal amounts of potassium (a common cause of mild hyperkalemia) A diet high in potassium Treatments that contain potassium
Most common cause of mild hyperkalemia is the use of drugs that decrease blood flow to the kidneys or prevent the kidneys from excreting normal amounts of potassium. Kidney failure can cause severe hyperkalemia on its own. Addison's disease can also cause hyperkalemia.
Hyperkalemia can develop after a large amount of potassium is released from the cells. The rapid movement of potassium from cells into blood can overwhelm the kidneys and result in life-threatening hyperkalemia.
What Makes the Potassium Level Increase?
Drugs or Other Circumstances
A diet containing potassium-rich foods
Intravenous treatments that contain potassium, such as total parenteral nutrition and blood transfusions
Decreased excretion in urine
Angiotensin-converting enzyme (ACE) inhibitors
Cyclosporine Some Trade Names SANDIMMUNE NEORAL (used to prevent of organ transplants)
Diuretics that help the kidneys conserve potassium, such as eplerenone, spironolactone Some Trade Names ALDACTONE , and triamterene Some Trade Names DYRENIUM
Nonsteroidal anti-inflammatory drugs
Tacrolimus Some Trade Names PROGRAF (used to prevent rejection of organ transplants)
Release of potassium from cells
Burns if severe
Crush injuries (involving the destruction of large amounts of muscle tissue)
Crack cocaine overdose
Exercise if strenuous and prolonged
Symptoms and Diagnosis
Mild hyperkalemia causes few, if any, symptoms. When hyperkalemia becomes more severe, it can cause abnormal heart rhythms. If the level is very high, the heart can stop beating.
Usually, hyperkalemia is first detected when routine blood tests are done or when a doctor notices certain changes on an electrocardiogram. To identify the cause, doctors determine which drugs people are taking and do blood tests to check kidney function.
For mild hyperkalemia, reducing consumption of potassium or stopping drugs that prevent the kidneys from excreting potassium may be all that is needed. If the kidneys are functioning, a diuretic may be given to increase potassium excretion. If needed, a resin that absorbs potassium from the digestive tract and passes out of the body in the stool can be given by mouth or enema.
For moderate to severe hyperkalemia, the potassium level must be reduced immediately. Calcium is given intravenously to protect the heart but does not lower the potassium level. Then insulin Some Trade Names HUMULIN NOVOLIN and glucose are given. They move potassium from blood into cells, thus lowering the potassium level in blood. Albuterol Some Trade Names PROVENTIL VENTOLIN (used mainly to treat asthma) may be given to help lower the potassium level. It is inhaled.
If these measures do not work or if people have kidney failure, dialysis may be necessary to remove the excess potassium.
Last full review/revision August 2008 by Larry E. Johnson, MD, PhD
Source: The Merck Manual Home Edition