title: Evaluation of HIV testing algorithms in Ethiopia: the role of the tie-breaker algorithm and weakly reacting test lines in contributing to a high rate of false positive HIV diagnoses.
abstract: BACKGROUND
  In Ethiopia a tiebreaker algorithm using 3 rapid diagnostic tests (RDTs) in series is used to diagnose HIV. Discordant results between the first 2 RDTs are resolved by a third 'tiebreaker' RDT. Médecins Sans Frontières uses an alternate serial algorithm of 2 RDTs followed by a confirmation test for all double positive RDT results. The primary objective was to compare the performance of the tiebreaker algorithm with a serial algorithm, and to evaluate the addition of a confirmation test to both algorithms. A secondary objective looked at the positive predictive value (PPV) of weakly reactive test lines.
  
  
  METHODS
  The study was conducted in two HIV testing sites in Ethiopia. Study participants were recruited sequentially until 200 positive samples were reached. Each sample was re-tested in the laboratory on the 3 RDTs and on a simple to use confirmation test, the Orgenics Immunocomb Combfirm® (OIC). The gold standard test was the Western Blot, with indeterminate results resolved by PCR testing.
  
  
  RESULTS
  2620 subjects were included with a HIV prevalence of 7.7%. Each of the 3 RDTs had an individual specificity of at least 99%. The serial algorithm with 2 RDTs had a single false positive result (1 out of 204) to give a PPV of 99.5% (95% CI 97.3%-100%). The tiebreaker algorithm resulted in 16 false positive results (PPV 92.7%, 95% CI: 88.4%-95.8%). Adding the OIC confirmation test to either algorithm eliminated the false positives. All the false positives had at least one weakly reactive test line in the algorithm. The PPV of weakly reacting RDTs was significantly lower than those with strongly positive test lines.
  
  
  CONCLUSIONS
  The risk of false positive HIV diagnosis in a tiebreaker algorithm is significant. We recommend abandoning the tie-breaker algorithm in favour of WHO recommended serial or parallel algorithms, interpreting weakly reactive test lines as indeterminate results requiring further testing except in the setting of blood transfusion, and most importantly, adding a confirmation test to the RDT algorithm. It is now time to focus research efforts on how best to translate this knowledge into practice at the field level.
  
  
  BACKGROUND
  Clinical Trial registration #: NCT01716299.
authors: Médecins Sans Frontières, Amsterdam, The Netherlands. Leslie.SHANKS@amsterdam.msf.org.
authors: Leslie
authors: L
authors: Shanks
authors: Médecins Sans Frontières, London, UK. ruby.siddiqui@london.msf.org.
authors: M Ruby
authors: MR
authors: Siddiqui
authors: Médecins Sans Frontières, Amsterdam, The Netherlands. jarmila_k@hotmail.com.
authors: Jarmila
authors: J
authors: Kliescikova
authors: London School of Hygiene and Tropical Medicine, London, UK. Neil.Pearce@lshtm.ac.uk.
authors: Neil
authors: N
authors: Pearce
authors: London School of Hygiene and Tropical Medicine, London, UK. cono.ariti@lshtm.ac.uk.
authors: Cono
authors: C
authors: Ariti
authors: Ethiopian Health and Nutrition Research Institute, Addis Ababa, Ethiopia. libse77m@gmail.com.
authors: Libsework
authors: L
authors: Muluneh
authors: Médecins Sans Frontières, Amsterdam, The Netherlands. erwan.pirou@amsterdam.msf.org.
authors: Erwan
authors: E
authors: Pirou
authors: Médecins Sans Frontières, Amsterdam, The Netherlands. Koert.Ritmeijer@amsterdam.msf.org.
authors: Koert
authors: K
authors: Ritmeijer
authors: Médecins Sans Frontières, Amsterdam, The Netherlands. jmasiga.jm@gmail.com.
authors: Johnson
authors: J
authors: Masiga
authors: Ethiopian Health and Nutrition Research Institute, Addis Ababa, Ethiopia. almaz_abe1@yahoo.com.
authors: Almaz
authors: A
authors: Abebe
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D002648:Child; D003955:Diagnostic Tests, Routine / Q000379:methods; D005002:Ethiopia / Q000453:epidemiology; D005189:False Positive Reactions; D005260:Female; D015658:HIV Infections / Q000175:diagnosis / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D012680:Sensitivity and Specificity; D055815:Young Adult
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