The potassium level in serum is about 0.4-0.5 mEq/L higher than the potassium level in whole blood or plasma (literature range, 0.1-1.2 mEq/L). This is attributed at least in part to potassium released from platelets during clotting. Serum specimens may have artifactual potassium level increase additional to that of normal clotting in patients with very high white blood cell (WBC) counts or platelet counts. The sodium concentration is about the same in serum, plasma, and whole blood. Potassium values increase 10%-20% if the patient follows the common practice of opening and closing his or her hand after a tourniquet is applied to the arm before venipuncture. Potassium can be increased in patient specimens by RBC hemolysis, sometimes considerably increased, which, unfortunately, is most often a laboratory artifact produced during venipuncture or when processing the specimen after venipuncture. Therefore, a pink or red color of plasma or serum usually means very inaccurate potassium values.