Nurses have always told me I have big, juicy veins and in the past there's never been any problem with getting blood drawn from them. However, since falling ill the nurses increasingly struggle to get enough blood out of my veins for blood tests. That's bad enough but I also have haemochromatosis (iron overload) and regularly have to get rid of a full unit of blood to keep this under control. Last time they only managed to get a quarter unit out of each arm and then the blood just refused to flow any more. BP was good and I was super-hydrated. Any ideas what could be causing this? Low blood volume or some sort of autonomic neuropathy? Sticky blood (that's probably not a medical term)? Something else? More importantly, any ideas how to overcome this?