Pseudohyperkalemia is a potentially dangerous phenomenon where falsely reported elevated potassium levels result in potentially unwarranted correction of potassium by sodium polystyrene or by dialysis in extreme cases. Overcorrection of potassium in a patient whose potassium is normal or low can lead to hypokalemia and potentially life-threatening consequences. Typical pseudohyperkalemia is thought to be a result of platelet-mediated release of potassium that occurs from the clotting process of a serum sample where no anticoagulant is present. As a result, pseudohyperkalemia is typically corrected when potassium is measured with a plasma sample where heparin and other preservatives are present in the collection tube. 1
Reverse pseudohyperkalemia is seen in patients with leukemia and lymphoma with significant lymphocytosis when laboratory studies demonstrate falsely elevated potassium. In reverse pseudohyperkalemia the potassium level from a plasma sample is falsely elevated despite the presence of an anticoagulant, as the process is independent of platelet activation and occurs as a result of white blood cell (WBC) breakdown. 2
For several decades, it has been suggested that the presence of heparin in tubes used to collect plasma is the cause of lysis of WBCs, presumably due to possible membrane fragility of these cells. Correction was recommended with the use of low-heparin-coated tubes. 3 The other proposed theory for reverse pseudohyperkalemia is that lysis of WBCs is primarily due to procedural handling: Several case reports suggest that pneumatic tube transport likely plays a strong role, as well as other factors, such as the length of time to the laboratory. 4-6
The authors report a case of a patient with chronic lymphocytic leukemia (CLL) who presented with significant reverse pseudohyperkalemia that later was determined to be dependent on pneumatic tube transport and independent of heparin.
Case Presentation
The patient, an 83-year-old man with a long history of asymptomatic CLL, was noted to have rapid WBC doubling time. His WBC counts had increased from 45 × 103/μL to 95 x 103/μL over the year preceding admission, then further increased to 300 x 103/μL in the month before admission.
A computed tomography (CT) scan of the chest, abdomen, and pelvis showed significant lymphadenopathy and splenomegaly. The patient presented to the hospital for treatment with a planned first cycle of bendamustine alone and subsequent cycles of bendamustine and rituximab. His medical history included Prinzmetal angina, coronary artery disease, wet macular degeneration, and benign prostatic hyperplasia. Notably, he had a documented history of hyperkalemia with potassium levels ranging from 4.7 mEq/L to 4.9 mEq/L over the previous year and was placed on a potassium-restricted diet.
On presentation, he reported no recent history of B symptoms of fever, night sweats, weight loss, and malaise. His labs oratory results showed an elevated potassium level of 6.1 mEq/L with repeated whole blood potassium of 8.2 mEq/L. An electrocardiogram (ECG) showed sinus rhythm, no noted T-wave abnormalities, and no conduction abnormalities. A physical exam was significant for normal muscle strength, cervical lymphadenopathy, and splenomegaly.
The patient was initially treated for hyperkalemia with insulin plus glucose and sodium polystyrene. He responded with mild improvement of his potassium level to 6.3 mEq/L, 5.6 mEq/L, and 5.1 mEq/L after receiving 5 doses of 30 g of polystyrene over multiple checks during a 24-hour period. Hemolysis results drawn at that time were unremarkable. It was noted that the patient had an elevated lactate dehydrogenase (LDH) level of 328 IU/L.