Objectives: This analysis assessed the impact of undisclosed HIV infection and antiretroviral therapy (ART) on national estimates of diagnosed HIV and ART coverage in Kenya.

Methods: HIV-positive dried blood spot samples from Kenya's second AIDS Indicator Survey were tested for an antiretroviral biomarker by liquid chromatography-tandem mass spectrometry. Weighted estimates of diagnosed HIV and ART coverage based on self-report were compared with those corrected for undisclosed HIV infection and ART use based on antiretroviral test results. Multivariate analysis determined factors associated with undisclosed HIV infection and ART use among persons on ART.

Results: The antiretroviral biomarker was detected in 42.5% [confidence interval (CI) 37.4–47.7] of HIV-infected persons. Antiretroviral drugs were present in 90.7% (CI 86.1–95.2) of HIV-infected persons reporting HIV-positive status and receiving ART, 66.7% (CI 59.9–73.4) reporting HIV-positive status irrespective of ART use, 21.0% (CI 13.4–28.6) reporting HIV-negative status, and 19.3% (CI 9.0–29.5) reporting no previous HIV test. After correcting for undisclosed HIV infection and ART use, diagnosed HIV increased from 46.9 to 57.2% and ART coverage increased from 31.8 to 42.8%. Undisclosed HIV infection while on ART was associated with being aged 25–39 years and not visiting a health provider in the past year, while younger age and higher wealth were associated with undisclosed ART use.

Conclusion: Substantial levels of undisclosed HIV infection and ART use among persons on ART were observed, resulting in diagnosed HIV underestimated by approximately 112000 persons and ART coverage by approximately 131000 persons. Supplementing self-reported ART status with objective measures of ART use in national population-based serosurveys can improve monitoring of HIV diagnosis and treatment targets in countries.