Renin

Renin is an enzyme, a protein that speeds up certain chemical reactions in your body. It's made by your kidneys. When your blood pressure or sodium decreases or your potassium increases, your kidneys release renin. That's because renin also acts as a hormone (a chemical messenger in your bloodstream that controls the actions of certain cells or organs) to help control your blood pressure.

A renin test (or renin and aldosterone test) is used to find out if your adrenal glands are making too much or too little aldosterone.