How much sodium in a pint of blood?

Updated June 2010

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 1.5 grams. That's less than I thought. It's only about 60% of the "daily value" (2.4 g). However, it is more than the amount of sodium in one can (340 mL) of V8 (880 mg), one serving (1/2 cup) of Campbell's Chicken Noodle soup (890 mg), or 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 1.5 grams. 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 = 3.22 g/L. Multiply by 473 mL and there you go (1.52 grams).

Here's another way to put it. One pint of blood has 1.52 grams of sodium, which is the amount found in 3.8 grams (or 0.8 teaspoons) of table salt (sodium chloride). Assuming you have 5 liters (5.3 quarts) of blood in your body, you have a total of 16.1 grams of sodium in your blood, which is the amount found in 8.5 teaspoons of salt.

Bottom line: you have about 8.5 teaspoons of table salt in your blood. In reality you have more sodium ions than chloride ions in your blood, but I think my estimate is good enough for cocktail party conversation.