Medical Convert is an iPhone app that allows you to quickly convert laboratory values between the conventional units (used in the US) and SI units (used in Europe, Canada, Australia and most of the world).
The interface is simple and clean allowing you to go in and out quickly.
The conversion factors were adapted from the AMA Manual of Style and can be found at this address:
http://www.amamanualofstyle.com/page/si-conversion-calculator