Electrolyte Relationships: Sodium and Potassium

Once you understand the functions and normal values for electrolytes, it is important to understand how some electrolyte levels are related to others. Often, an imbalance of one electrolyte is related to an imbalance of another electrolyte so understanding these relationships can assist in determining the root cause of, and treatment for, certain electrolyte imbalances. In this series, we will examine some of the how levels of sodium, potassium, calcium, and magnesium are related to other electrolytes. This post will focus on sodium and potassium.

You can find discussions about other electrolyte relationships in two other blogs:

Electrolyte Relationships: Calcium, Phosphorus, and Vitamin D
Electrolyte Relationships: Magnesium

The Relationship between Sodium and Potassium

Sodium is the main cation in the ** body fluid outside the cells, such as blood and interstitial fluid (extracellular), and **potassium is the main cation in the body cells (intracellular). Cell membranes contain sodium-potassium pumps that regulate the balance of sodium and potassium intra- and extra- cellularly. This can help you remember that sodium and potassium have an inverse relationship, meaning when sodium levels rise, potassium levels fall, and vice versa.

The Role of the Kidneys

The kidneys are mainly responsible for maintaining a balance. When the potassium level rises in the body, the kidneys will excrete more sodium, and when the potassium levels fall, the kidneys will excrete less sodium causing the levels to rise. This is why patients with high sodium levels are encouraged to eat foods high in potassium to encourage the kidneys to excrete more potassium.

The Effects of Magnesium

While potassium is the main cation in the cell, magnesium is the second most abundant intracellular cation. Potassium deficiency can be related to, or exacerbated by, magnesium deficiency as these electrolytes have a similar relationship. When magnesium levels fall, potassium levels also fall, and this is referred to as secondary potassium depletion. Of note, potassium levels falling do not cause magnesium levels to fall.

Treatment with Magnesium

Low magnesium levels can cause more potassium to leave the cells and be excreted by the kidneys, decreasing the overall level in the body. For this reason, you should keep an eye on the magnesium levels in patients at risk for hypokalemia, like patients taking diuretics. The administration of magnesium is often appropriate when attempting to correct hypokalemia.