Hepatitis B viral load in dried blood spots: A validation study in Zambia

Background: Access to hepatitis B viral load (VL) testing is poor in sub-Saharan Africa (SSA) due toeconomic and logistical reasons.Objectives: 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.Study design: Paired plasma and DBS samples from HIV-HBV co-infected Zambian adults were analyzedfor HBV VL using the COBAS AmpliPrep/COBAS TaqMan HBV test (Version 2.0) and for HBV genotypeby direct sequencing. We used Bland-Altman analysis to compare VLs between sample types and bygenotype. Logistic regression analysis was conducted to assess the probability of an undetectable DBSresult by plasma VL.Results: Among 68 participants, median age was 34 years, 61.8% were men, and median plasma HBV VLwas 3.98 log IU/ml (interquartile range, 2.04–5.95). Among sequenced viruses, 28 were genotype A1 and27 were genotype E. Bland–Altman plots suggested strong agreement between DBS and plasma VLs. DBSVLs were on average 1.59 log IU/ml lower than plasma with 95% limits of agreement of −2.40 to −0.83 logIU/ml. At a plasma VL ≥2,000 IU/ml, the probability of an undetectable DBS result was 1.8% (95% CI:0.5–6.6). At plasma VL ≥20,000 IU/ml this probability reduced to 0.2% (95% CI: 0.03–1.7)