Why does no blood come when you have a test?

When you have a blood test, a small needle is inserted into a vein in your arm. The needle is attached to a tube that collects the blood. The blood is then sent to a laboratory for testing.

If no blood comes out when the needle is inserted, it may be because the needle is not in the vein properly. The phlebotomist (the person who draws your blood) may try again to insert the needle in a different spot.

If the needle is in the vein properly but no blood is coming out, it may be because you are dehydrated. Drinking plenty of fluids before your blood test can help to prevent this from happening.

If you are still having trouble giving blood, you may want to talk to your doctor. There may be an underlying medical condition that is causing the problem.