Gas chromatography mass spectrometry (GC-MS) was used to separate and quantitate PG and FA. One 3/16” punch from DBS or 6uL of washed RBC were used to prepare samples for analysis by methylation with 3N methanolic HCl. PG and FA were extracted with hexane, dried and reconstituted in toluene for analysis. Reference ranges for measured markers, C16:0, C18:0 and C18:1 PG and palmitic (C16:0) and stearic (C18:0) FA and 10 analyte ratios were established by the analysis of 720 and 476 control DBS and RBC samples, respectively. Preliminary disease ranges were established for RCDP1 (N=18 DBS, 6 RBC), RCDP2 (N=4 DBS), RCDP4 (N=2 RBC) and ZSD (N=2 DBS, 1 RBC). Post-analytical decision support tools were created using Collaborative Laboratory Integrated Reports (CLIR, https://clir.mayo.edu
) post-analytical interpretive tools were created to generate an integrated score and a likelihood of disease for each condition and to provide a conclusive differential diagnosis between paired condition (for example, RCDP1 vs. RCDP2).