What Is Serum K?

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  • Written By: Clara Kedrek
  • Edited By: Jessica Seminara
  • Last Modified Date: 13 January 2019
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The term serum K refers to the concentration of potassium in the blood. Potassium is often abbreviated as K because this is its symbol as displayed on the periodic table of the elements. The level of potassium in the blood is a routinely checked laboratory value because the mineral plays an essential role in the proper functioning of the human body. Either high or low levels of this substance in the blood can cause dangerous complications, including cardiac arrest.

Potassium plays an important role in the body. It is considered to be an electrolyte, as it is a charged chemical species that is dissolved in body fluids. Most of the body's potassium is located within its cells, meaning that only a small percentage of the body's total potassium stores circulates in the blood. Maintaining varying concentrations of potassium in different parts of the body is important to for its proper functioning, including the coordination of the beating of the heart. Potassium's critical role in human physiology can be evidenced by the fact that its levels are carefully adjusted by the kidneys, the adrenal glands, and the gastrointestinal tract.


Levels of potassium in the blood, often referred to as the serum K levels, are commonly checked laboratory values. The level is reported as part of a basic metabolic panel, which also provides information regarding serum levels of sodium, bicarbonate, urea, and creatinine. Normal serum K levels range from 3.5 to 5.1 milli-equivalents per liter (mEq/L), although these standard values can vary slightly depending on what laboratory is performing the test.

High serum K results in a condition called hyperkalemia. A number of different diseases can cause this state, including kidney failure or problems with the adrenal glands. Medications administered to treat a variety of conditions, including diuretics and blood pressure medications, can cause the level of potassium in the blood to rise. Symptoms of hyperkalemia can include weakness, impaired reflexes, a decreased rate of breathing, and irregular heart rhythms. The abnormal heartbeats in particular can be dangerous to patients, progressing into cardiac arrest if the potassium levels are not lowered fast enough. Immediate treatment options for elevated serum K include giving calcium, sodium bicarbonate, insulin, and glucose.

Having low levels of serum K can also be very dangerous. Causes of this condition, referred to as hypokalemia, include chronic vomiting, certain kidney diseases, and excessive sweating. Medications including diuretics, antibiotics, and laxatives can also lower blood potassium levels. Symptoms of hypokalemia include weakness, nausea, vomiting, thirst, and increased urination. As with hyperkalemia, low blood potassium levels can also cause potentially dangerous alterations in the beating of the heart, so the condition is treated promptly by administering supplemental potassium to the patient.


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