All of the properties were modeled after measurements from the International Union of Pure and Applied Chemistry (IUPAC) color book series. I believe the Silver Book was the primary source originally. RDen or Relative Density is defined in a Google search of ‘Relative Density IUPAC Book’ as “Ratio of density to a reference density, usually the density of water at 4 degrees C; in the older literature this is called specific gravity. The electronic search returned from the IUPAC Gold Book. The IUPAC has their own organizational website.
I also went into RELMA and searched Property:RDen, found all related terms and chose one to see comprehensive detail. The definition in RELMA has additional information for your benefit. I presume you already have read within the LOINC User’s Guide, Table 8 – Example LOINC properties, Chapter 4 and Appendix E.
Thank you for the question; I hope this helps!
This reply was modified 5 days, 3 hours ago by Pam Banning. Reason: Remove typeface edit language
Now I know in the future where to search for this information. And yes I’ve been using the Table 8: Example LOINC Properties as my main reference which has worked 99% of the time to answer my questions and further search. I apparently just failed to see the footnote referring to the IUPAC silver book.