Thousands of Hongkongers have opted out of the city’s organ donor registry, seemingly as a form of subtle protest against proposals to establish deeper medical ties with mainland China. Between December and April, there were more than 5,700 applications to withdraw from the centralised organ donor registry, the government revealed on Monday. That is “significantly higher” than the normal rate of withdrawals. The trigger appears to have been a life-saving operation carried out in December on a four-month-old baby girl in Hong Kong, who was in need of a heart…