title: Hepatitis B viral load in dried blood spots: A validation study in Zambia.
abstract: BACKGROUND
  Access to hepatitis B viral load (VL) testing is poor in sub-Saharan Africa (SSA) due to economic and logistical reasons.
  
  
  OBJECTIVE
  To demonstrate the feasibility of testing dried blood spots (DBS) for hepatitis B virus (HBV) VL in a laboratory in Lusaka, Zambia, and to compare HBV VLs between DBS and plasma samples.
  
  
  METHODS
  Paired plasma and DBS samples from HIV-HBV co-infected Zambian adults were analyzed for HBV VL using the COBAS AmpliPrep/COBAS TaqMan HBV test (Version 2.0) and for HBV genotype by direct sequencing. We used Bland-Altman analysis to compare VLs between sample types and by genotype. Logistic regression analysis was conducted to assess the probability of an undetectable DBS result by plasma VL.
  
  
  RESULTS
  Among 68 participants, median age was 34 years, 61.8% were men, and median plasma HBV VL was 3.98logIU/ml (interquartile range, 2.04-5.95). Among sequenced viruses, 28 were genotype A1 and 27 were genotype E. Bland-Altman plots suggested strong agreement between DBS and plasma VLs. DBS VLs were on average 1.59logIU/ml lower than plasma with 95% limits of agreement of -2.40 to -0.83log IU/ml. At a plasma VL ≥2,000IU/ml, the probability of an undetectable DBS result was 1.8% (95% CI: 0.5-6.6). At plasma VL ≥20,000IU/ml this probability reduced to 0.2% (95% CI: 0.03-1.7).
  
  
  CONCLUSIONS
  In a Zambian laboratory, we observed strong agreement between DBS and plasma VLs and high sensitivity in DBS at plasma VL ≥2,000IU/ml. As HBV treatment expands, DBS could increase access to HBV VL testing and care in SSA settings.
authors.affiliation: Department of Medicine, University of Alabama at Birmingham, USA; Centre for Infectious Disease Research in Zambia, Lusaka, Zambia; School of Medicine, University of Zambia, Lusaka, Zambia. Electronic address: mjv3@uab.edu.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Vinikoor
authors.affiliation: Institute of Infectious Diseases, University of Bern, Switzerland.
authors.forename: Samuel
authors.initials: S
authors.lastname: Zürcher
authors.affiliation: Centre for Infectious Disease Research in Zambia, Lusaka, Zambia; School of Medicine, University of Zambia, Lusaka, Zambia.
authors.forename: Kalo
authors.initials: K
authors.lastname: Musukuma
authors.affiliation: Centre for Infectious Disease Research in Zambia, Lusaka, Zambia.
authors.forename: Obert
authors.initials: O
authors.lastname: Kachuwaire
authors.affiliation: Department of Infectious Diseases, University Hospital Bern, Switzerland.
authors.forename: Andri
authors.initials: A
authors.lastname: Rauch
authors.affiliation: Department of Obstetrics and Gynecology, University of North Carolina at Chapel Hill, USA.
authors.forename: Benjamin H
authors.initials: BH
authors.lastname: Chi
authors.affiliation: Institute of Infectious Diseases, University of Bern, Switzerland.
authors.forename: Meri
authors.initials: M
authors.lastname: Gorgievski
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Switzerland.
authors.forename: Marcel
authors.initials: M
authors.lastname: Zwahlen
authors.affiliation: Department of Infectious Diseases, University Hospital Bern, Switzerland; Institute of Social and Preventive Medicine, University of Bern, Switzerland; Department of Infectious Diseases, University of Dakar, Senegal.
authors.forename: Gilles
authors.initials: G
authors.lastname: Wandeler
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001769:Blood / Q000821:virology*; D003890:Desiccation; D005260:Female; D006509:Hepatitis B / Q000175:diagnosis*; D006515:Hepatitis B virus / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D008875:Middle Aged; D025202:Molecular Diagnostic Techniques / Q000379:methods; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods*; D019562:Viral Load / Q000379:methods*; D055815:Young Adult; D015024:Zambia
keywords: Africa; Dried blood spots; HIV/AIDS; Hepatitis B virus; Viral load