Hi Logger :)
This is an online resource- not a book, but it could help someone tremendously who needs to understand what their test results mean, OR like me, who is having to decide which Blood Tests they want to have run:
1. left click on 'index of tests'
2. select the test about which you are curious
3. Once it takes you to the selected test page, keep left-clicking on 'next' to get more info as you go through successive pages.
The pages as you click through are full of useful links as well..