"Mothers arm left black after blood test"

I am writing this following the (in my opinion) disgusting level of care taken when my mother goes to have her blood checked (she is on Warfarin). The last four times my 81 year old mother has had her blood tested by the same nurse. Each time my mothers arm has been left with an enormous black bruise. I thought this was happening due to my mothers age but apparently it didnt happen before. Today my mother had this nurse again and when she told her the nurse daughter was concerned about the bruising the nurse told my mum she had to see her GP about this. I am outraged! What a cheek! It seems to me that this so called Nurse is uncaring, but incredibly arrogant!!! I've told my mother to get the testing done at the surgery in future. If her arm turns black again. I will be making a formal complaint. Has anyone else had this experience?