BACKGROUND: Insulin therapy is most effective if dosage titrations are done regularly and frequently, which is seldom practical for most clinicians, resulting in an insulin titration gap. The d-Nav Insulin Guidance System (Hygieia, Livonia, MI, USA) is a handheld device that is used to measure glucose, determine glucose patterns, and automatically determine the appropriate next insulin dose. We aimed to determine whether the combination of the d-Nav device and health-care professional support is superior to health-care professional support alone. METHODS: In this multicentre, randomised, controlled study, we recruited patients from three diabetes centres in the USA (in Detroit MI; Minneapolis, MN; and Des Moines IA). Patients were eligible if they were aged 21-70 years, diagnosed with type 2 diabetes with a glycated haemoglobin (HbA1c) concentration of 7.5% or higher (>/=58 mmol/mol) and 11% or lower (