title: Fifth-generation digital immunoassay for prostate-specific antigen by single molecule array technology.
abstract: BACKGROUND
  Measurement of prostate-specific antigen (PSA) in prostate cancer patients following radical prostatectomy (RP) has been hindered by the limit of quantification of available assays. Because radical prostatectomy removes the tissue responsible for PSA production, postsurgical PSA is typically undetectable with current assay methods. Evidence suggests, however, that more sensitive determination of PSA status following RP could improve assessment of patient prognosis and response to treatment and better target secondary therapy for those who may benefit most. We developed an investigational digital immunoassay with a limit of quantification 2 logs lower than current ultrasensitive third-generation PSA assays.
  
  
  METHODS
  We developed reagents for a bead-based ELISA for use with high-density arrays of femtoliter-volume wells. Anti-PSA capture beads with immunocomplexes and associated enzyme labels were singulated within the wells of the arrays and interrogated for the presence of enzymatic product. We characterized analytical performance, compared its accuracy with a commercially available test, and analyzed longitudinal serum samples from a pilot study of 33 RP patients.
  
  
  RESULTS
  The assay exhibited a functional sensitivity (20% interassay CV) <0.05 pg/mL, total imprecision <10% from 1 to 50 pg/mL, and excellent agreement with the comparator method. All RP samples were well within the assay measurement capability. PSA concentrations following surgery were found to be predictive of prostate cancer recurrence risk over 5 years.
  
  
  CONCLUSIONS
  The robust 2-log improvement in limit of quantification relative to current ultrasensitive assays and the validated analytical performance of the assay allow for accurate assessment of PSA status after RP.
authors: Quanterix Corporation, Cambridge, MA, USA. dwilson@quanterix.com
authors: David H
authors: DH
authors: Wilson
authors: David W
authors: DW
authors: Hanlon
authors: Gail K
authors: GK
authors: Provuncher
authors: Lei
authors: L
authors: Chang
authors: Linan
authors: L
authors: Song
authors: Purvish P
authors: PP
authors: Patel
authors: Evan P
authors: EP
authors: Ferrell
authors: Herbert
authors: H
authors: Lepor
authors: Alan W
authors: AW
authors: Partin
authors: Dan W
authors: DW
authors: Chan
authors: Lori J
authors: LJ
authors: Sokoll
authors: Carol D
authors: CD
authors: Cheli
authors: Robert P
authors: RP
authors: Thiel
authors: David R
authors: DR
authors: Fournier
authors: David C
authors: DC
authors: Duffy
mesh_terms: D001330:Electronic Data Processing; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D006801:Humans; D008297:Male; D008832:Microchemistry / Q000379:methods; D008875:Middle Aged; D010865:Pilot Projects; D017430:Prostate-Specific Antigen / Q000097:blood*; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000601:surgery; D040081:Protein Array Analysis / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
chemical_list: D017430:Prostate-Specific Antigen