Potassium is a type of mineral called an electrolyte that helps your cells and organs work. Your body needs it to digest food, keep your heart beating right, and many other activities. You get most of your potassium from foods. Your body uses what it needs, and your kidneys put the rest into your urine as waste.
Why Do I Need the Test?
Your doctor may do it if your potassium was checked from a blood sample and your results showed something may not be right. A second test with urine can help them narrow down the reasons.
Your doctor also may order the urine test if:
For the test, you’ll need to either pee into a cup once or collect several samples over 24 hours and save them in a larger container.
How It Differs From a Blood Test
Your potassium level can be different in your urine than it is in your blood. Normally, your kidneys filter it out of your blood and get rid of it when you pee. For example, diabetes or some heart medicines can make your blood potassium level high but your urine potassium level low. On the other hand, kidney disease, diarrhea, or too much sweating can do the opposite. That’s why sometimes your doctor needs to test both.
Usually, blood potassium levels in adults should be between 3.6 and 5.2 millimoles per liter, or mmol/L.
Hyperkalemia. This happens when your blood potassium levels are 7 mmol/L or higher. This can happen if your kidney can’t get rid of enough potassium through your urine. It can cause muscle weakness, irregular heartbeats, and other problems.
Conditions that can lead to hyperkalemia include:
Hypokalemia. Very low levels of blood potassium -- below 2.5 mmol/L -- can be dangerous. As with levels that are too high, symptoms of low potassium can include muscle weakness that starts in your legs and moves up. If your blood potassium is too low, your kidneys will normally try to hang on to it and pass less into your urine.
Hypokalemia could result from:
- Vomiting or diarrhea
- Too much aldosterone, a hormone that helps control your blood pressure and blood volume
- Not enough potassium from foods or supplements
- Acetaminophen (Tylenol) overdose