Is the level of eloctrocytes measurered by taking a urine or a blood sample?

Both: You can check electrolytes in urine & serum (blood). Serum is the common one.

Electrolytes: Levels of electrolytes are measures most commonly in serum, however, they are also measured in urine. Looking for a basis metabolic panel to see how you are doing overall, blood is drawn. Looking to see if you are metabolizing well and utilizing or wasting nutrients, urine can be used. With your history of renal disease they would check your electrolytes in your urine to eval your disease process.