The value of your sample for research will be greatly increased if it is accompanied by data. This may include, for example, your age, gender and details of any medical conditions you may have and how well you are in the time after your sample was taken. In most cases this is now held on computers, which can raise concerns about how securely it is kept.
Retention of records which provide your identity is very strictly controlled through the Data Protection Act (more details are given on the website of the Information Commissioners's Office). In addition researchers must comply with the Caldicott Guidelines which restrict information on a strict "need to-know" basis.