- Blood drawing No more than 450 milliliters (30 tablespoons, or 15 ounces) of blood will be taken from adults over a 6-week period. A maximum of 7 ml (1/2 tablespoon) of blood per kilogram (2.2. pounds) of body weight will be obtained from children within the same time period, with no more than 3 ml/kg taken at any one time.