A woman who would lose her vision if there was not enough male blood available to treat her condition is urging more men to donate.
Jo Daniels, 39, from Bristol, has the autoimmune disease Sjogren's syndrome, which attacks her tear glands and leaves her with painful ulcers on her corneas.
She uses a daily eye serum, made from male blood, to keep her sight.
Only 41% of new blood donors in England last year were men.
The high level of iron present in male blood makes it especially helpful to patients who rely on regular life-saving transfusions.
Unlike men, women produce antibodies during pregnancy which makes their blood unviable for numerous specialist transfusions and blood-based products, such as complete blood transfusions in newborn babies.
'In the dark'
Mrs Daniels's life turned upside down when her sight began to deteriorate at an alarming rate.
She told BBC News: "My eyes were itchy for a while before my vision suddenly became blurry and painful.
"Over the course of four weeks, I went from seeing normally to being completely in the dark.
"To make matters worse, it came on over the Christmas period, so I couldn't get help very quickly.
"I was worried I would lose my career and not be able to see my young daughter grow up."
Numerous treatments failed to help Mrs Daniels and she became resigned to the fact she may never be able to regain her vision.