I need a blood transfusion. If I go on the scales afterwards will my mass have increased (not lost any blood)?

It partly depends on what you are receiving. It is now rare to transfuse whole blood. If you are being given a blood transfusion to bring up your haemoglobin levels you will be given packed red cells. You will be receiving something that weighs approximately 470 g. That is less than 1/2 kg. That is approximately 1 lb so it may just show on your scales.

If you weigh yourself before and immediately after your weight HAS TO increase by the weight of the transfusion.

I had a blood transfusion a year or so ago and my weight change was only about 1-2 pounds (more).

You will weigh about a pound more

no it still won't

yes.

But remember, you will be LOW when you start, so the value at the end should be NORMAL