Under‐ and overdosing insulin in the hospital: A retrospective cohort study of dose deviation and patient outcomes

AIMS: Glycaemic abnormalities during hospitalization are common and linked to morbidity and mortality, yet little is known about how deviations from guideline-recommended insulin dosing affect outcomes. The aim of this study is to examine whether deviation from an expected insulin dose in non-critically ill hospitalized adults with type 2 diabetes, compared with guideline-concordant dosing, is associated with mortality, length of stay or dysglycaemias. METHODS: This retrospective cohort study included adults with type 2 diabetes hospitalized at a tertiary academic medical centre (2010-2025) who received ≥ 24 h of subcutaneous insulin. The expected total daily insulin dose (TDID) was calculated based on guideline-concordant dosing using the ADA-recommended range (0.3-0.6 units/kg/day), and the observed TDID was derived from medication records. Patients were classified as undertreated (< 0.3 units/kg/day), guideline-concordant (0.3-0.6 units/kg/day) or overtreated (> 0.6 units/kg/day). Outcomes included length of stay, and 30-day mortality, hypoglycaemia and hyperglycaemia. RESULTS: Among 3430 hospitalized adults with type 2 diabetes receiving subcutaneous insulin, 37.6% received guideline-concordant dosing, 43.7% were undertreated, and 18.7% were overtreated. Undertreatment was independently associated with increased 30-day mortality (aHR 1.273, 95% CI 1.024-1.583; p = 0.03), while overtreatment was not. Undertreated patients had more hyperglycaemia and longer hospital stays (p < 0.001), whereas hypoglycaemia rates were similar between groups. CONCLUSION: Deviation from guideline-based insulin dosing is common in hospitalized adults with type 2 diabetes. Undertreatment was associated with increased 30-day mortality and prolonged hospitalization. Monitoring insulin dose deviation may help identify patients at risk for adverse outcomes.