Whenever I have a patient with elevated potassium, my brain immediately jumps to Addison’s disease or urinary disease, because this was drilled into our heads during veterinary school.

If the rest of the lab work is unremarkable and especially if the patient is otherwise healthy, an elevated platelet count can be a cause of the potassium being elevated in the serum.

Hyperkalemia due to thrombocytosis has been described frequently in the literature, but is often overlooked. It occurs because platelet activation during clotting is associated with potassium release.  

The platelets degranulate when clotting in vitro, releasing potassium into the serum. For a more accurate potassium level in patients with thrombocytosis, you can measure potassium in the plasma (which contains non-activated platelets).

Just a reminder to keep thrombocytosis on your list as a possible cause of elevated serum potassium.