Useful links

Easy to understand information on Pathology tests can be found at Lab Tests Online

The Royal College of Pathologists has some useful information on Pathology in general, as well as some good educational resources. 

The Association for Laboratory Medicine also has some good resources

The series Medicine in a Nutshell is a great education tool of short videos on a huge range of topics in medicine in general, but includes a lot of good content relating to lab tests (See this on PSA, or this on the immune system)