Can thrombocytosis (high platelet count) cause hyperkalemia (elevated potassium levels)?

Pseudohyperkalemia from Thrombocytosis

Yes, high platelet counts cause falsely elevated serum potassium (pseudohyperkalemia), not true hyperkalemia—this is a critical distinction that prevents unnecessary and potentially dangerous treatment. 1, 2

Mechanism and Clinical Significance

Pseudohyperkalemia occurs when platelets release intracellular potassium during the clotting process in vitro, artificially elevating serum potassium measurements while plasma potassium remains normal. 1, 3

Key characteristics:

• Serum potassium exceeds plasma potassium by more than 0.4 mmol/L 3
• Plasma potassium levels remain normal despite elevated serum values 2, 4
• No true metabolic disturbance exists—this is purely a laboratory artifact 2

Prevalence and Platelet Count Thresholds

The relationship between platelet count and pseudohyperkalemia is dose-dependent:

• Hyperkalemia incidence increases from 9% at platelet counts <250×10⁹/L to 34% when platelets exceed 500×10⁹/L 2
• Traditionally described at extreme thrombocytosis (>1,000×10⁹/L), but occurs at much lower elevations 2, 4
• A highly significant positive correlation exists between platelet count and serum potassium (R=0.998) 4

Populations at Highest Risk

Myeloproliferative disorders show the highest rates of pseudohyperkalemia:

• Primary thrombocythemia: 75.7% of patients 4
• Polycythemia vera: 75% of patients 4
• Myelofibrosis: 50% of patients 4
• Reactive thrombocytosis: 34.5% of patients 4

Overall, 60% of all patients with thrombocytosis from any cause demonstrate pseudohyperkalemia 4

Diagnostic Algorithm

When encountering elevated serum potassium with thrombocytosis, follow this sequence:

1. Check platelet count immediately—if elevated, suspect pseudohyperkalemia 1, 3

2. Measure both serum AND plasma potassium simultaneously 1, 3

   • If serum K⁺ exceeds plasma K⁺ by >0.4 mmol/L, this confirms pseudohyperkalemia 3
   • Plasma potassium will be normal in pseudohyperkalemia 2, 4

3. Assess for true hyperkalemia causes (only if plasma potassium is also elevated) 5, 6:

   • Renal insufficiency (eGFR <15 mL/min/1.73 m²) 7
   • RAAS inhibitors, potassium-sparing diuretics, NSAIDs 6
   • Metabolic acidosis 6

4. Obtain ECG—pseudohyperkalemia will NOT show ECG changes (peaked T waves, widened QRS) 5, 6

Critical Management Pitfalls

Do NOT treat pseudohyperkalemia as true hyperkalemia—this can cause dangerous iatrogenic hypokalemia. 3, 4

Common errors to avoid:

• Initiating aggressive hyperkalemia treatment (calcium, insulin/glucose, dialysis) based solely on serum potassium without checking plasma levels 3
• Altering dialysis prescriptions in renal patients with thrombocytosis without confirming true hyperkalemia 3
• Failing to recognize pseudohyperkalemia leads to unnecessary anxiety, testing, and potentially harmful interventions 8, 4

The European Heart Journal emphasizes ruling out pseudohyperkalemia before treatment, as failing to do so is a major pitfall in hyperkalemia management 5

When Pseudohyperkalemia Signals Underlying Disease

Persistent unexplained pseudohyperkalemia may be the first clue to an undiagnosed myeloproliferative disorder. 8

• If thrombocytosis is newly discovered during hyperkalemia workup, immediate hematologic evaluation is warranted 8
• Essential thrombocythemia and other myeloproliferative disorders are commonly diagnosed this way 8, 4
• Normalizing platelet counts (through treatment of the underlying disorder) resolves the pseudohyperkalemia 8