C4A and short chain acyl-CoA dehydrogenase deficiency: Figures 1A,B show the scatter plots for the C4 vs. C4/C2 ratios and differences among SCADD, IBDD, and no-gene mutation cases. In the initial NBS approach, the cutoff value for C4 was 0.04–0.42 μmol/L. The mean plasma concentrations of C4 in individuals with SCADD and individuals with IBDD were 1.42 and 1.39 μmol/L, respectively. Further statistical analysis revealed a significant difference between individuals with SCADD or IBDD and the no-mutation group (p < 0.001).