That's what I was wondering as I sat in the blood donation center yesterday with a large-bore needle in my cephalic vein, having finally succumbed to the nagging of my conscience (and the nagging of the American Red Cross ).
The answer, as far as I can tell, is about 720 mg. That's less than I thought. It's only about 30% of the "daily value" (2.4 g). It's less than the amount of sodium in one can (340 mL) of V8 (880 mg), less the amount in one serving (1/2 cup) of Campbell's Chicken Noodle soup (890 mg), and even less than the amount in one large Vlasic pickle (880 mg). So next time you finish drinking a bottle of apple juice after donating blood, you should slap yourself in the forehead and say, "I could've had a V8!"
For the curious, here's how I came up with 720 mg. One pint of blood is 473 mL. The normal concentration of sodium in the blood is 135-145 mEq/L (according to this handy site ). I picked the mean, 140 mEq/L, which is equivalent to 140 mmol/L (since sodium is a monovalent ion). There are 23 grams of sodium in one mole (information you find on a periodic table ), so 140 mmol/L = 1.52 g/L. Multiply by 473 mL and there you go.