Potassium

What is Potassium?

Potassium is an electrolyte concentrated inside cells that is essential for nerve signaling, muscle contraction, and a steady heartbeat. Blood levels are kept within a narrow range, largely by the kidneys.

Most of the body's potassium sits inside cells, and the blood carries only a small fraction, yet that blood level is critical because both high (hyperkalemia) and low (hypokalemia) values can disturb the heart's rhythm. The kidneys are the main regulators, matching potassium excreted in urine to potassium taken in through food, while hormones and acid-base status can shift potassium between cells and blood. Levels are affected by kidney function, certain blood pressure and diuretic medications, vomiting or diarrhea, and how a blood sample is drawn and handled, since red-cell breakdown in the tube can falsely raise a reading. Because of its effect on the heart, markedly abnormal potassium is treated as a priority, and results are often confirmed before acting.

What to know about Potassium

Understanding Potassium means knowing what it reflects, what tends to move it, and the signs that suggest it’s worth a closer look — so you can bring the right questions to your next appointment.

How to read a value in context

A normal potassium result means the value sits within the tight population reference interval that supports steady nerve and heart function. Because sample handling can artificially raise potassium and levels can shift quickly with medications or illness, an unexpected abnormal value is often rechecked before it is acted on.

Lifestyle factors that influence this marker

• Eat a generally balanced diet that naturally includes potassium-rich fruits and vegetables, rather than large potassium supplements or salt substitutes on your own
• Stay hydrated and replace fluids sensibly during illness with vomiting or diarrhea
• Keep up regular activity and habits that support overall kidney and heart health
• Talk to your doctor before changing your diet, using salt substitutes, or adjusting supplements, especially if you take blood pressure medications or have kidney disease

Tests often checked alongside this

• Creatinine and eGFR — kidney function is the main driver of potassium balance
• Sodium and chloride — measured together on the electrolyte panel
• Bicarbonate (CO2) — acid-base shifts move potassium in and out of cells
• Magnesium — low magnesium can make low potassium hard to correct

How this can show up in how you look and feel

• Low potassium can be associated with muscle weakness, cramps, and palpitations
• High potassium can be associated with muscle weakness and dangerous changes in heart rhythm
• Mild abnormalities are often silent and detected only on a blood test

What can affect this marker

• Kidney function
• Medications such as certain diuretics, ACE inhibitors, and potassium supplements
• Vomiting, diarrhea, or other fluid losses
• Acid-base status and how the blood sample is collected and handled

What to track over time

• Potassium alongside kidney markers and the electrolyte panel
• Medications known to raise or lower potassium
• Episodes of vomiting, diarrhea, or dehydration
• Any palpitations or muscle weakness to report

What to ask your doctor

• Could a medication of mine be affecting my potassium?
• Should an unexpected result be repeated to rule out sample issues?
• Is my kidney function influencing this level?
• Do I need any dietary changes, and are salt substitutes safe for me?

This glossary entry is for informational purposes only and is not a substitute for professional medical advice. Read our Medical Disclaimer.