I live in London, England.
I was a regular blood donor until November 2006. On that occasion I went to the blood donation centre to give a donation, only to have them tell me that I was slightly anaemic and - for my own good - they wouldn't be taking my blood. They said that perhaps I should see my GP in case there was some issue such as a dietary deficiency, however I shouldn't worry.
My GP did a test and said I had abnormally low white cell count, as well as mild anaemia (low red cell count). He referred me to the Royal Free Hospital haemotology department. He said it wasn't leukaemia as apparantly (most) leukaemias have a high not low white cell count.
Initially the haemotologist said I had an 'idiopathic' low white cell count meaning 'unknown cause'. They did several tests over a few weeks and could find no cause. Eventually they did a hip bone biopsy and that's when I began to really worry. Eventually the haemotologist called me to his office to break the news. He said that because I was a blood donor it had been caught very early and was probably treatable. I was pretty scared but they explained the treatment (Cladribine chemotherapy) to me and my wife and the following week I went in for the chemo. This was in March 2007.
Since then I have had blood counts every 6 months and so far everything is OK.
The moral of the story (for people you know without HCL) is - be a blood donor because that's one way that they can find blood problems very early.