Abstract
Introduction
Pseudohyperkalemia is an in vitro elevation in measured serum potassium caused by cellular potassium release during clot formation or specimen processing. It should be considered in patients with marked thrombocytosis and otherwise unexplained hyperkalemia to prevent unnecessary and potentially harmful potassium-lowering treatment.
Case Info
A 73-year-old female with CALR exon 9 double-mutated, JAK2 V617F-negative, MPL-negative, and BCR:ABL1-negative essential thrombocytosis was followed for recurrent thrombocytosis and intermittent hyperkalemia. She had previously developed severe pancytopenia while receiving hydroxyurea, with a marrow biopsy showing marked hypocellularity (5–10%) without fibrosis or blast excess, prompting subsequent cautious cytoreductive management. After hydroxyurea was held because of treatment-associated cytopenias, her platelet count increased from 408 × 10³/µL to 791 × 10³/µL. Concurrent potassium levels were repeatedly borderline elevated at 5.3 mmol/L. After hydroxyurea reinitiation at 500 mg daily, platelet counts trended down to 603 × 10³/µL. Potassium levels also trended down to 4.7 mmol/L. Throughout this period, kidney function was preserved, and bicarbonate remained normal at the highest potassium measurement, with no evidence of renal failure or metabolic acidosis. The recurrent elevation in potassium, temporally associated with marked thrombocytosis and with no alternative metabolic explanation, was most consistent with thrombocytosis-associated pseudohyperkalemia.
Disc Clinical
In thrombocytosis, platelets release potassium during coagulation, which can artifactually increase serum potassium despite normal in vivo potassium concentration. Pseudohyperkalemia is supported by a serum-to-plasma potassium difference greater than 0.4 mmol/L; confirmation requires paired plasma potassium collected in a lithium-heparin tube and/or rapidly analyzed whole-blood potassium. This case was complicated by concurrent Lisinopril exposure, which could contribute to true hyperkalemia; however, potassium elevations were documented before angiotensin-converting-enzyme inhibitor initiation and occurred despite stable renal function and normal bicarbonate. The temporal relationship between recurrent thrombocytosis and potassium elevation therefore raised strong concern for pseudohyperkalemia.
Conclusion
Apparent hyperkalemia in patients with essential thrombocythemia and substantial thrombocytosis should prompt evaluation for pseudohyperkalemia before treatment escalation. Paired serum and plasma or whole-blood potassium testing is essential to establish the diagnosis, avoid inappropriate therapy, and prevent iatrogenic hypokalemia.