Purpose: To examine the performance of an instrument to assess adherence based on a visual analogue scale, compared to an instrument based on 3-day recall, using unannounced pill counts in the place of residence as the gold standard.
Method: We prospectively assessed adherence to antiretroviral therapy in 84 marginally housed indigent HIV-infected patients who were receiving stable antiretroviral therapy in San Francisco, California, with three adherence assessments over no more than 4 months.
Results: Mean adherence using the visual analogue scale, 3-day recall, and unannounced pill count methods were 82.5%, 84.2%, and 75.9%, respectively. The correlation between visual analogue scale and unannounced pill count was high (r = 0.76) and was not statistically different from that between 3-day recall and unannounced pill count (r = 0.71; p =.52). Both methods were also similarly inversely correlated with HIV viral load (r = -0.49 and -0.34, respectively; p =.22 for the difference in the correlations). The visual analogue scale correlation with unannounced pill count was stable over time and remained high in all subpopulations examined.
Conclusion: A visual analogue scale to assess adherence was performed as well as a more complicated 3-day recall instrument in this diverse population. Given its simplicity, the visual analogue scale adherence instrument will be useful in research and may be useful in routine patient care.