A schematic workflow illustrating the steps involved in the differential analysis of RA and OA synovial fluid proteome. Proteins from RA and OA synovial fluid were extracted and depleted to remove the 14 most abundant proteins using multiple affinity removal system, Human-14. The depleted protein from RA and OA were then digested with trypsin and labeled with iTRAQ reagents, 117 and 116 respectively. The labeled samples were pooled and subjected to fractionation using strong cation exchange chromatography. The fractions were then analyzed on a LTQ-Orbitrap Velos mass spectrometer. The MS/MS data obtained was searched against Human RefSeq 50 database using Sequest and Mascot search algorithms. Validation of the iTRAQ quantitation data was carried out using multiple reaction monitoring and Western blot.