What causes high potassium on a blood test: kidneys, medications, extra potassium or a sample problem

High potassium on a blood test usually comes from kidneys that clear less potassium, medications that hold it in, extra potassium from supplements or salt substitutes, or a sample problem, where potassium leaked out of blood cells after the draw. One high result isn't a diagnosis.

A 2021 CMAJ review defines hyperkalemia (high potassium) as 5.0 mmol/L or higher. In people with normal kidney function, true hyperkalemia is uncommon, and a sample problem is the usual explanation.

Why does a kidney baseline matter for potassium?

In over 2 million potassium results from US veterans who'd been in hospital, high potassium was three to nearly five times as common with chronic kidney disease (CKD). CKD often goes unnoticed: about 1 in 7 US adults have it, and only 12% know.

So potassium reads best next to creatinine, the main kidney marker. Numia Health, a physician-ordered, at-home blood testing service in Greater Vancouver, reports both on its Electrolytes Panel, giving you a kidney baseline to track.

Which medications raise potassium?

Never stop a prescribed medication to change a number. These drugs protect the heart and kidneys, and the CMAJ review says the harms of reducing or stopping them appear to outweigh the harms of high potassium. Your prescriber decides what changes.

Could the result be a sample problem?

One of the most common causes of a falsely high potassium, called pseudohyperkalemia, is hemolysis: red blood cells breaking open during collection and spilling potassium into the sample. Very high platelet or white-cell counts, and cold before the sample is processed, can do the same.

Whether to repeat is your clinician's call, including for a Numia result. A possible sample problem is never a reason to ignore it.

When should you seek care now?

Most high results, Numia's included, mean a prompt call, not an emergency:

• Call 9-1-1 if high potassium comes with a too-slow, too-fast or fluttering heartbeat, or muscle weakness.
• Go to the emergency department if you're told your potassium is above 6.0 mmol/L, as the CMAJ review advises for most people.
• Otherwise, call the clinician who ordered the test promptly, or HealthLink BC at 8-1-1.

A home panel like Numia's is built for baselines and trends, not urgent care.

Where does Numia fit?

The usual route, publicly funded when clinically indicated, means an appointment, a lab visit, a wait and a follow-up. In BC, a request for "electrolytes" covers sodium and potassium only, unless more is requested. Numia Health puts the steps in one place: a licensed Canadian physician approves your requisition (lab order) online in about 3 minutes, and a BC-licensed clinician does a 10-minute morning draw at home. The panel reports potassium, sodium, chloride, creatinine and urea, needs no fasting, and sends plain-English results to the Numia app in 7 days. Out-of-range results are physician-reviewed with next steps, an optional wellness consultation is available, and Numia is an HSA-eligible service.

Frequently asked questions

What causes high potassium in a blood test?

If your kidneys are healthy, usually a sample problem such as hemolysis. When it's real, reduced kidney function and medications like ACE inhibitors, ARBs, spironolactone and trimethoprim are the common causes.

Should I stop my blood pressure pill if my potassium is high?

No. Call your prescriber, who may repeat the test or adjust the dose. Numia sells testing, not prescriptions, so dose decisions stay with them.

Can salt substitutes raise potassium?

Yes. Some, like No Salt and Nu-Salt, use potassium chloride. HealthLink BC advises avoiding potassium salt substitutes if you have hyperkalemia.