title: Comparison of low-abundance biomarker levels in capillary-collected nonstimulated tears and washout tears of aqueous-deficient and normal patients.
abstract: OBJECTIVE
  Low tear volume limits the use of nonstimulated (NS) microcapillary tear collection in aqueous-deficient (AD) patients. Adding a small amount of "washout" fluid to the eye prior to tear collection is a potentially viable alternative method for abundant proteins, but is relatively untested for low-abundance biomarkers. This study determined the feasibility of the washout (WO) method as an NS alternative for low-abundance biomarkers. NS and WO biomarker profiles were compared between AD patients and non-AD controls to determine if the two methods identify the same intergroup differences.
  
  
  METHODS
  Matching NS and WO tears were collected from 48 patients by micropipette, the WO sample after instillation of 10 μL saline. Tear cytokine levels were measured by 27-Plex Bio-Rad assay. Bland-Altman analyses for each biomarker determined the agreement between tear sample types. Patients were grouped as AD or non-AD based on Schirmer score to determine if NS profile between-group differences were preserved in WO tears.
  
  
  RESULTS
  Bland-Altman plots showed good biomarker level agreement between NS and WO tears for most cytokines. Five biomarkers, among those most often cited as differing in AD dry eye, differed significantly between non-AD and AD groups in both tear types. Additional biomarker differences were seen in NS tears only.
  
  
  CONCLUSIONS
  The WO tear collection method is a viable alternative to NS tears for many low-abundance biomarkers and is able to replicate major NS tear differences between dry eye groups. More subtle intergroup differences are lost in WO samples because of reduced statistical power.
authors.affiliation: Department of Vision Sciences, School of Optometry, University of Alabama-Birmingham, Birmingham, AL 35294, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Guyette
authors.forename: Larezia
authors.initials: L
authors.lastname: Williams
authors.forename: My-Tho
authors.initials: MT
authors.lastname: Tran
authors.forename: Tammy
authors.initials: T
authors.lastname: Than
authors.forename: John
authors.initials: J
authors.lastname: Bradley
authors.forename: Lucy
authors.initials: L
authors.lastname: Kehinde
authors.forename: Clara
authors.initials: C
authors.lastname: Edwards
authors.forename: Mark
authors.initials: M
authors.lastname: Beasley
authors.forename: Roderick
authors.initials: R
authors.lastname: Fullard
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000378:metabolism; D002197:Capillary Action; D016207:Cytokines / Q000378:metabolism*; D015352:Dry Eye Syndromes / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012965:Sodium Chloride / Q000008:administration & dosage*; D013048:Specimen Handling / Q000379:methods; D013666:Tears / Q000378:metabolism*; D055815:Young Adult
chemical_list: D015415:Biomarkers; D016207:Cytokines; D005136:Eye Proteins; D012965:Sodium Chloride
keywords: aqueous deficient; non-stimulated tears; tear biomarkers; washout tears