Although the causes of hyperkalemia are legion, normal renal function and lack of compatible EKG findings may be a clue to pseudohyperkalemia (PH), which is commonly defined as a difference between serum and plasma [K+] > 0.4 mEq/L when the samples are obtained concurrently, remain at room temperature and are tested within an hour of collection1; plasma is obtained in heparinized tubes which prevent platelet aggregation, degranulation and K+ release. In the absence of visible hemolysis, PH may be related to the lysis of high number of WBCs (particularly when fragile as seen in CLL) or platelets.
Early recognition of PH is important to avoid inappropriate treatment that may result in serious hypokalemia. Several factors in the technique by which blood is collected and processed may lead to PH, including prolonged tourniquet use, fist clenching, inappropriate needle diameter, excessive force with syringe draw, vacuum tubes, and inappropriate temperature or delayed processing of the specimen.
When PH is suspected, concurrent K+ measurement by conventional phlebotomy and by a blood gas specimen or a venous specimen by gentle aspiration via a butterfly needle into a non-vacuum tube is recommended2.
- Avelar T. Reverse pseudohyperkalemia in a patient with chronic lymphocytic leukemia. Perm J 2014;18:e150-e152.
- Chan JS, Baker SL, Bernard AW. Pseudohyperkalemia without reported hemolysis in a patient with chronic lymphocytic leukaemia. BMJ Case Reports 2012;doi:10.1136/bcr.12.2011.5330