A normal potassium level in the blood is between 3.6 and 5.2 millimoles per liter (mmol/L). Low potassium A potassium level below 2.5 mmol/L is referred to as hypokalemia that can be life-threatening. High potassium A potassium level above 6.0 mmol/L is referred to as. hyperkalemia that can be dangerous and requires immediate treatment. Hyperkalemia, also known as high potassium, is a condition where there is too much potassium in the blood. It can be dangerous and lead to serious heart problems. The rate at which serum potassium rises is more important than the level itself. Causes Kidney disease: When