GSTM1 and periodontitis: Concentrations of Hb in the oral, nasal and pharyngeal cavities that act as a niche for S. aureus, S. pyogenes, C. diphtheriae and N. meningitidis have not been directly defined, but investigations into salivary Hb as a potential diagnostic tool for periodontitis have identified an average of 6 μg/mL of Hb in saliva of healthy individuals [126].