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.

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?

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