S100A9 and lobular neoplasia: Indeed, S100 proteins are of relatively low molecular weight (S100A8: ~11 kDa, S100A9: ~13 kDa; S100A8/A9 heterodimer: 23.9 kDa; S100A12: 21 kDa), which may result in partial ‘loss’ through filtration in healthy individuals that is further increased in LN.3637 Since proteins with a molecular weight between 14 and 45 kDa are partially filtered through the glomerulus and are therefore a physiological component of both the serum/plasma and urine proteome, increased filtration and associated ‘loss’ may therefore account for increased urine/serum ratios in patients with active LN.