Updated FTP location. Absolute quantification of protein was performed by MALDI-LTQ using scramble internal standard (sIS) peptide. Mixtures of serial dilutions of fibrinogen peptides (final concentration: 50, 100, 250, 500 and 1000 fmol/μL), equal amounts of corresponding sIS peptides (final concentration: 500 fmol/μL) and serial dilutions of digested serum (final concentration: 0, 0.025, 0.05, 0.25 and 0.5 μg/μL) were analyzed by MALDI-MS/MS. We also analyzed immunoprecipitated (IP) α-fibrinogen in 0.05-5 μL of plasma by MALDI-MS/MS.