Objective: Thrombocytosis, particularly in children, can lead to spurious biochemical findings such as pseudohyperkalemia, which may result in unnecessary interventions if unrecognized. This study aimed to evaluate the effect of platelet count on serum potassium levels in children with thrombocytosis and to analyze the association between potassium levels and the etiological factors of thrombocytosis.

Materials and Methods: In this retrospective study, 1899 pediatric patients with platelet counts >600×10⁹/L were analyzed over one year. After excluding conditions that could affect serum potassium (e.g., essential thrombocytosis, anemia, polycythemia/leukocytosis, renal or hepatic disease, and hyperbilirubinemia), 1210 cases of reactive thrombocytosis were included. Patients with available serum potassium measurements and follow-up data at 3 and 6 months were assessed.

Results: The mean age of the 1210 patients was 2.7±3.4 years, and 54.8% were male. Thrombocytosis was primarily due to infections (71.8%) and surgery, burns, or trauma (28.2%). Platelet counts ranged from 600×10⁹/L to 2.193×10⁹/L, and serum potassium levels from 2.47 to 9.3 mEq/L. Hyperkalemia occurred in 20.4% of patients, increasing with higher platelet counts (16.7% for 600–900×10⁹/L, 29.1% for 900–1000×10⁹/L, and 33.5% for >1000×10⁹/L). Significant decreases in platelet and potassium levels were observed at 3- and 6-month follow-ups (p<0.001). A weak positive correlation was observed between platelet and potassium levels (r=0.187), more pronounced in infection-related cases (r=0.218). Potassium increased by 0.06 mEq/L for every 100×10⁹/L rise in platelet count, with a significant correlation only above 1000×10⁹/L (r=0.196, p=0.038).

Conclusion: Pseudohyperkalemia is a common yet overlooked phenomenon in pediatric thrombocytosis. Recognizing the quantitative platelet–potassium relationship can prevent diagnostic confusion and unnecessary treatment.

Keywords: Hyperkalemia, thrombocytosis, platelet count, pseudohyperkalemia