Hyperkalemia refers to the condition in which the concentration of the electrolyte potassium

Potassium

Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 (K⁺) in the blood is elevated. Extreme hyperkalemia is a medical emergency

Medical emergency

A medical emergency is an injury or illness that is acute and poses an immediate risk to a person's life or long term health. These emergencies may require assistance from another person, who should ideally be suitably qualified to do so, although some of these emergencies can be dealt with by the...

 due to the risk of potentially fatal abnormal heart rhythms (arrhythmia).

Normal serum potassium levels are between 3.5 and 5.0 mEq/L; at least 95% of the body's potassium is found inside cells

Intracellular

Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...

, with the remainder in the blood. This concentration gradient is maintained principally by the Na+/K+ pump.
Symptoms are fairly nonspecific and generally include malaise

Malaise

Malaise is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease. Malaise is often defined in medicinal research as a "general feeling of being unwell"...

, palpitations and muscle weakness

Muscle weakness

Muscle weakness or myasthenia is a lack of muscle strength. The causes are many and can be divided into conditions that have true or perceived muscle weakness...

; mild hyperventilation may indicate a compensatory response to metabolic acidosis

Metabolic acidosis

In medicine, metabolic acidosis is a condition that occurs when the body produces too much acid or when the kidneys are not removing enough acid from the body. If unchecked, metabolic acidosis leads to acidemia, i.e., blood pH is low due to increased production of hydrogen by the body or the...

, which is one of the possible causes of hyperkalemia.