title: Ferric reducing ability of tears in healthy subjects-diurnal variation and dependence on defined demographic data.
abstract: OBJECTIVE
  The assay of the ferric reducing ability of tears (FRAT) can be useful for monitoring ocular antioxidant capacity in clinical settings. FRAT diurnal variation was evaluated in healthy subjects and its relation with age, sex, body mass index, and ferric reducing ability of plasma (FRAP) were studied.
  
  
  METHODS
  FRAT of 10-microl tear samples collected with capillary tubes from 68 healthy subjects (age 10 to 92 yrs, 46 women, 22 men) were measured after 0, 3, 5, and 10 min of incubation with Fe(3 +). FRAT diurnal variation was estimated in 11 subjects, with tear samples collected every 4 hr during the day. Comparison of FRAT versus FRAP was determined in 20 subjects.
  
  
  RESULTS
  Mean FRAT after 10-min incubation reached 207.7 +/- 136.8 micromol/l. No differences were found between FRAT of men and women. Only donor age correlated with FRAT (rho = 0.40, p < 0.01). Subjects <or= 59 years had lower FRAT levels than those age > 59 yrs (179.4 +/- 95.4 versus 237.2 +/- 151.7 micromol/l, p < 0.01). For all investigated times of incubation, FRAT was approximately two times lower than FRAP (p < 0.01). FRAT revealed diurnal variation, with the highest value at 08:00 hours, upon awakening.
  
  
  CONCLUSIONS
  The significance of age-matched controls and the specific time of the day for tears collection should be considered in the trial design and investigations with FRAT as a marker of the ocular antioxidant defense system.
authors.affiliation: Medical Centre Sal-Med, Lodz, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Kowalski
authors.forename: Anna
authors.initials: A
authors.lastname: Bielecka-Kowalska
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Bielecka-Roszkiewicz
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Dziankowska-Zaborszczyk
authors.forename: Jeffrey
authors.initials: J
authors.lastname: de Graft-Johnson
authors.forename: Janusz
authors.initials: J
authors.lastname: Szemraj
authors.forename: Anna
authors.initials: A
authors.lastname: Zwolinska
authors.forename: Dariusz
authors.initials: D
authors.lastname: Nowak
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D000975:Antioxidants / Q000378:metabolism; D002648:Child; D002940:Circadian Rhythm; D005123:Eye / Q000378:metabolism; D005260:Female; D005290:Ferric Compounds / Q000737:chemistry*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D010949:Plasma / Q000378:metabolism; D012016:Reference Values; D013666:Tears / Q000378:metabolism*; D055815:Young Adult
chemical_list: D000975:Antioxidants; D005290:Ferric Compounds