The Revised International Staging System (R-ISS) includes variables included in the original ISS (serum beta-2 microglobulin and serum albumin), while also including the additional prognostic information obtained from serum LDH and high-risk chromosomal abnormalities detected by interphase fluorescent in situ hybridization (iFISH) after CD138 plasma cell purification.

The revised ISS stages are as follows:

Stage I: ISS stage I and standard-risk CA by iFISH and normal LDH
Stage II: Not R-ISS stage I or III
Stage III: ISS stage III and either high-risk CA by iFISH or high LDH

References

Palumbo A et al
Revised International Staging System for Multiple Myeloma: A Report From International Myeloma Working Group.
J Clin Oncol. 2015 Sep 10;33(26):2863-9. doi: 10.1200/JCO.2015.61.2267. Epub 2015 Aug 3.