Expert: Neha Dahiya MD - 6/4/2009

Question
How much blood is required to conduct a blood test?
Background: My 86 yr old mother was admitted to hospital with a chest infection. The keep taking her blood daily, and (have difficulty finding her veins - very uncomfortable for her)and say that she is anaemic. She says: "What do you expect, you are always taking my blood, but never bringing any back!"

Answer
Hello:

At a given time 3 to 6 ml of blood may be drawn to do most of the routine blood tests. If some more specialized tests are required then more blood may be drawn.
Withdrawing this quantity of blood occasionally will not contribute to anemia.

I am not sure for what particular investigation blood is withdrawn for your mother. In case of infection , a larger volume will be drawn to determine nature of infectious organism in the body by doing culture of blood.

I wish your mother a speedy recovery and good health