Objectives: Organizational strategies for implementing eHealth tools influence patient and provider use of portal technology. This study examines whether the intensity of bidirectional secure portal messaging is associated with improved clinical outcomes.; Material and Methods: This is a retrospective cohort analysis of 101 019 patients with diabetes or hypertension (11 138 active portal users) who received primary care within the Ochsner Health System between 2012 and 2014. Propensity score-adjusted multivariable fixed effects regression panel analysis was used to examine associations between intensity of "medical advice" portal messaging and glucose/blood pressure control.; Results: Most portal users rarely used medical advice messaging. A higher proportion of patients who were age 50 years and older, female, white non-Hispanic, and with co-morbid diabetes and hypertension had higher frequency and intensity of medical advice messaging. Study findings revealed a dose-response effect of the intensity of messaging on glucose control, whereby, compared to nonportal users, each level of messaging among portal users was associated with greater decreases in HbA1c (beta estimate [95% CI]: none -0.28 (-0.34 to -0.22); low -0.28 (-0.32 to -0.24); medium -0.41 (-0.52 to -0.31); high -0.43 (-0.60 to -0.27), all P <= .001). There was no observed effect on blood pressure.; Conclusions: The digital divide exists not only between portal users and nonusers but also among portal users. Research exploring the relationship between intensity of bidirectional secure messaging and health outcomes for a broader scope of chronic conditions is needed. Future implementation research must also elucidate best practices that enhance not only the use of portals by patients and providers, but how they use portals.
