Why do burn patients have increased potassium in urine?

Answer 1

Normally, potassium is an intracellular electrolyte. Sodium is primarily an extracellular ion.

Cellular destruction releases intracellular ions like potassium into the extracellular spaces such as the blood. The blood then transfers potassium into the urine to establish electrolytic homeostasis.

Answer 2

I would have to disagree with the above answer.

That isn't how the kidney works nor is there typically enough cellular lysis close enough to big vessels to allow dumping of potassium before the cells just cook.

With burns, the body goes into shock and responds as if it has lost a lot of fluid. The kidneys respond to this by releasing renin which activates enzymes to make angiotensin II which then stimulates release of aldosterone. Aldosterone is a hormone that acts on the kidney to increase resorptions of sodium (and there for water since water follows sodium). In order to resorb sodium from the filtered blood (i.e. urine), cells pump sodium into the cell and potassium out of the cell.

Therefore, there is more potassium in the urine and less sodium in the urine. That means there is less potassium in the serum.