title: Impact of definitions of loss to follow-up (LTFU) in antiretroviral therapy program evaluation: variation in the definition can have an appreciable impact on estimated proportions of LTFU.
abstract: OBJECTIVE
  To examine the impact of different definitions of loss to follow-up (LTFU) on estimates of program outcomes in cohort studies of patients on antiretroviral therapy (ART).
  
  
  METHODS
  We examined the impact of different definitions of LTFU using data from the International Epidemiological Databases to Evaluate AIDS-Southern Africa. The reference approach, Definition A, was compared with five alternative scenarios that differed in eligibility for analysis and the date assigned to the LTFU outcome. Kaplan-Meier estimates of LTFU were calculated up to 2 years after starting ART.
  
  
  RESULTS
  Estimated cumulative LTFU were 14% and 22% at 12 and 24 months, respectively, using the reference approach. Differences in the proportion LTFU were reported in the alternative scenarios with 12-month estimates of LTFU varying by up to 39% compared with Definition A. Differences were largest when the date assigned to the LTFU outcome was 6 months after the date of last contact and when the site-specific definition of LTFU was used.
  
  
  CONCLUSIONS
  Variation in the definitions of LTFU within cohort analyses can have an appreciable impact on estimated proportions of LTFU over 2 years of follow-up. Use of a standardized definition of LTFU is needed to accurately measure program effectiveness and comparability between programs.
authors.affiliation: Centre for Infectious Disease Epidemiology & Research, School of Public Health & Family Medicine, University of Cape Town, Falmouth Building, Anzio Road, Observatory, Cape Town, 7925 South Africa. agrimsrud@gmail.com
authors.forename: Anna Thora
authors.initials: AT
authors.lastname: Grimsrud
authors.forename: Morna
authors.initials: M
authors.lastname: Cornell
authors.forename: Matthias
authors.initials: M
authors.lastname: Egger
authors.forename: Andrew
authors.initials: A
authors.lastname: Boulle
authors.forename: Landon
authors.initials: L
authors.lastname: Myer
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000188:drug therapy*; D000293:Adolescent; D000328:Adult; D000353:Africa, Southern; D044966:Anti-Retroviral Agents / Q000627:therapeutic use*; D018791:CD4 Lymphocyte Count / Q000706:statistics & numerical data; D015331:Cohort Studies; D016208:Databases, Factual; D005260:Female; D006801:Humans; D059012:Lost to Follow-Up; D008297:Male; D008875:Middle Aged; D015397:Program Evaluation; D009626:Terminology as Topic; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D044966:Anti-Retroviral Agents
keywords: Antiretroviral therapy; Cohort; Loss to follow-up; Program outcomes; Retention; Survival analysis