How much DNA and RNA can be expected from human blood cells?

Human blood consists of leukocytes, thrombocytes, and erythrocytes. Since only the leukocytes contain a nucleus they are most important when estimating the amount of nucleic acid in human blood. Thrombocytes and erythrocytes do not contain a cell nucleus, although they do contain minor amounts of RNA. Blood of a healthy individual usually contains 4–7 x 106 leucocytes per milliliter blood. This means that the DNA content can vary between 30 and 40 µg/ml blood depending on the donor. The RNA content is relatively low and varies between 1–5 µg/ml blood. This means that blood contains about 10x more DNA than RNA. Because of this imbalance, a DNase digest is usually recommended during RNA isolation from human blood.

Please note that the number of leukocytes per millilitre blood can vary from 2 x 106 during immunosuppression, to 40 x 106 during inflammation, up to 500 x 106 during leukemia. The DNA and RNA content will vary accordingly.