Looking for basic - or background - information on a topic is best done in textbooks or other resources that compile the known and standard information into a single resource.
Harrison's principles of internal medicinePubMed can also give you background information that expands your background understanding.
In most cases, when searching in these resources one word or phrase is better than a long question or multiple concepts.
These resources are more clinically focused but can be used also like an encyclopedia about some topics.
Symptoms & DDX Resources
Symptoms and differential diagnositic information is often buried in a number of our resources. However, a few tools (both online and for your smart phone/PDA) have special tools to help with this process.
Dr. Gates has found a very helpful text within Access Medicine - Symptoms to Diagnosis: An Evidence Based Guide. Presented through a series of cases of patients complaining of a specific issue, then walks you through buiding the DDX and prioritizing it, and making the diagnosis. Unlike the interactive tools that give you list, this text helps explain the thinking process. Topics include a variety of non-specific complaints from low back pain to weight loss to GI bleeding, to abdominal pain. Check out Chapter 1 as an overview of the diagnostic process.
The books we have include one that helps explain the thinking process (Symptom to Diagnosis) with topics that include a variety of non-specific complaints from low back pain to weight loss to GI bleeding, to abdominal pain. One book has a list of mnemonics (Collins' book) as well as the symptom info. Another book (Syed & Rasul's book) is organized by body areas and the last one (DDX of Common Complaints) focuses on the most common symptions and presents the way a doctor might pursue to diagnosis (images & tests).
Isabel - the last one in the list - is an up and coming tool that is starting to be integrated into the EMR environment. This free version should be very helpful for many look ups.
Also listed below are some of the interactive DDX tools and their advantages.
Symptom to Diagnosis by 
Differential Diagnosis in Internal Medicine by 
The Patient History by 
Differential Diagnosis in Primary Care by 
Differential Diagnosis in Primary Care by 
Differential Diagnosis of Common Complaints by Online Look-up Tools
More DDX Checker Tools
Check out our home grown tool or use one of the mnemonics.
Looking up information about the results of lab tests are mostly background questions. The following resources are easy to use tools to find very reliable information about the normal values, reference ranges, and more.
Henry's Clinical Diagnosis and Management by Laboratory Methods by 
Ferri's Clinical Advisor by 
Pocket Guide to Diagnostic Tests by 
Delmar's Guide to Laboratory and Diagnostic Tests by 
