Why Doctors Order Laboratory Tests http://www.kidshealth.org/parent/system/medical/labtest2.html
An excellent reference, written for parents to help explain diagnostic procedures to their children. Because its intended audience is children, the descriptions are brilliant in their simplicity and structure. You can search for a test in two ways: 1) by name, or 2) by the kind of sample that is collected or type of imaging.
Wired for Health http://www.wiredforhealth.gov.uk/
Health information at the touch of a button for young people and their teachers, Wired for Health aims to provide accurate and engaging information on health.