Frequently, increased serum potassium levels are due to mishandling of the blood specimen, according to Mayo Clinic. In cases of true high serum potassium levels, an underlying condition such as kidney disease or a side effect of angiotensin-converting enzyme inhibitors, among other causes, may be the source of the problem.
Mayo Clinic explains that blood potassium levels are normally 3.6 to 5.2 millimoles per liter. A level higher than 7.0 millimoles per liter requires immediate investigation and treatment of the underlying cause.
Sometimes people with slightly elevated potassium levels report fatigue, muscle weakness and nausea, according to eMedicineHealth. Since potassium is instrumental in keeping the heart beating at a normal rate, severely elevated potassium levels can cause life-threatening heart arrhythmias and require immediate medial attention.