Table 3.

Most relevant findings about nonenzymatic antioxidant biomarkers.

Specimen	Method of detection	Healthy vs. COPD	In COPD stages
Protein SH groups
Blood	Ellman's assay	↓ [19, 20, 26, 38, 54, 104]/nd [29]	↓ [38]/nd [19, 26]
	Quantification of albumin via chemistry automated analyzer	↓ [36]
	Subtraction of GSH from total thiols	↓ [51]/nd [30, 52]
Reduced GSH
Blood	Ellman's assay in plasma	↓ [18, 24, 30, 31, 33, 35, 51, 52]/nd [33]	nd [30]
	Ellman's assay in whole blood	↓ [40, 96]	nd [40]
	Ellman's assay in erythrocytes	↓ [16, 27]	↓ [16]
	Colorimetric determination in erythrocytes	nd [46]
Sputum	Subtraction of oxidized glutathione from total GSH	nd [105]
	Colorimetric determination	↓ [31]
BALF	Reaction with Ellman's reagent in plate reader	↓ [106]
Total GSH
Blood	Reaction with Ellman's reagent and glutathione reductase in plasma		nd [42]
	Reaction with Ellman's reagent and glutathione reductase in whole blood	↑ [19, 26]	↑ [19]
Sputum	Spectrophotometry following reaction with Ellman's reagent and glutathione reductase	↑ [105, 107]
Total thiols
Blood	Reaction with Ellman's reagent in plasma	↓ [49]/↑ [72]	↓ [30]
Total antioxidant capacity
Blood	FRAP assay	↓ [19, 26]	↓ [19, 26, 111]
	TEAC assay	↓ [30, 39, 53, 104, 110–112]/nd [47, 89]	nd [30]
	Assay based on preventing oxidation of orthodianisidine molecules by hydroxyl radicals	↓ [21, 22, 87]
BALF	Spectrophotometric monitoring of inhibition of ABTS radical formation by antioxidants	nd [113]

↑ indicates increased levels; ↓ indicates decreased levels; nd: no difference.