Strategies for querying LoincCode table by category

I need a way to determine if a particular group of rows are specific to Chemistry, Hematology, etc.; which field(s) do I need to use to make this determination. Is there any documentation that explains this?

Yes, you can use the CLASS field of the LOINC database for exactly this purpose. Take a look at Appendix B of the LOINC User’s Guide for a detailed listing of the classes. If you are using RELMA, you can restrict your searches to any particular class (or any other hierarchy node) by going over to the “hierarchy and search restrictions” tab and selecting the node at which you want to limit your search.

The upcoming RELMA release (5.0) will have a way to do this from the search command line, so stay tuned…