|MadSci Network: Medicine|
Dear Barbara, This is a very interesting question! Here are some considerations I made in calculating the number of calories in a pint of blood. The strategy is to express the components of blood in terms of grams of protein, lipid and carbohydrate. Then convert the grams to calories. An alternative and more direct way of determining the number of calories in a donated pint of blood would be to dry it down (to remove the water), and then burn it in a calorimeter to calculate how much heat is generated from the blood. I can calculate a reasonable number for calories associated with the plasma (non-cellular portion) of the blood, but I can only make a rough approximation of the calories obtained from the red blood cells. 1. A blood donation usually is 400 to 495 ml (for calculations I will use 500 ml). 2. Assume an average hematocrit of 40% for a woman (40% red blood cells, 60% plasma by volume). 500 ml x 40% = 200 ml (plasma volume) *Plasma glucose: The average plasma glucose concentration is 90 mg/dL (or 0.9 mg/ml). 200 ml x 0.9 mg/ml = 180 mg of glucose in plasma portion of donated blood = 0.18 gm of glucose Caloric content of glucose is 3.4 kcal/g, therefore 0.18 gm of glucose = 0.612 kcal *Plasma protein: The average plasma total protein concentration is 7 g/dL (or 70 mg/ml) 200 ml x 70 mg/ml = 14,000 mg of protein in plasma portion of donated blood = 14 gm of protein Caloric content of protein is 4.0 kcal/g, therefore 14 gm of protein = 56.0 kcal *Plasma lipid: The average plasma total lipid concentration is 600 mg/dL (or 6 mg/ml). 200 ml x 6 mg/ml = 1,200 mg of lipid in plasma portion of donated blood = 1.2 gm of lipid Caloric content of lipid is 9.0 kcal/g (long chain fatty acids), therefore 1.2 gm of lipid = 10.8 kcal **Therefore total calories in donated plasma = 0.6 + 56 + 10.8 = 61.4 kcal Calories derived from red blood cells: I will make the assumption that the predominant component of RBC's is hemoglobin, which is a protein. Therefore: Whole blood hemoglobin in females averages around 14 g/dL (or 140 mg/ml) The donated whole blood volume is 500 mls so 500 ml x 140 mg/ml = 70,000 mg of protein (hemoglobin) from donated RBC's = 70 gm of protein Caloric content of protein is 4.0 kcal/g, therefore 70 gm of protein = 280 kcal *****THEREFORE TOTAL ESTIMATED CALORIC CONTENT IN ONE STANDARD BLOOD DONATION *****EQUALS = 280 (from RBCs) + 61.4 (from plasma) = **341.4kcal**** References: Clinical Diagnosis & Management by Laboratory Methods by J.B. Henry, 18th Edition (1991), page 1366-1372 Facts and Formulas by R.C. Rollings, (1984) page 61 I hope this answers your question! ....mark fung, md/phd
Try the links in the MadSci Library for more information on Medicine.