No. Blood and cells have completely different electrolyte compositions.
To clarify, there is intracellular fluid (inside the cells) and extracellular fluid, outside the cells. There are actually two different extracellular fluids, blood and Interstitial fluid.
Potassium and magnesium are mostly in the intracellular fluid and sodium and chloride in the extracellular fluid.
Blood is extremely regulated because it is so important while the interstinial fluid is regulated mostly by aldosterone. You wont see problems with electrolytes in the blood, if you do its probably too late. Blood is only 20% of extracellular fluid. But if there are problems with Interstitiall fluid you wont see it in the blood.