http://www.labtestsonline.org/
“Lab Tests Online has been designed to help you, as a patient or family caregiver, to better understand the many clinical lab tests that are part of routine care as well as diagnosis and treatment of a broad range of conditions and diseases.”–From the website. It is non-commerical, patient centered, peer-reviewed, and is a product of the collaboration of a number of professional societies representing the laboratory community who have partnered to be responsible for the content of different areas found on this site.