Comparison of the prevalence of type 2 diabetes mellitus (T2DM) in adults aged 25-64 years in selected Pacific Island countries using whole blood and plasma glucose cut-off points. Unit records of STEPwise approach to Surveillance (STEPS) surveys obtained from Fiji, Samoa, and Tonga Ministries of Health; T2DM prevalence recalculated using whole blood and plasma cut-off points. Shaded bars indicate T2DM prevalence based on correct glucose cut-off points for the glucose meter used (fasting blood glucose [FBG] ≥6.1 mmol/L for early surveys1,3,5 ; fasting plasma glucose [FPG] ≥7.0 mmol/L for later surveys),2,4,6 whereas open bars show T2DM prevalence based on incorrect glucose cut-off points (FPG ≥6.1 mmol/L for later surveys).2,4,6 Highlights Incorrect glucose cut-off points were applied to the Fiji 2011, Samoa 2013, and Tonga 2012 STEPS surveys. This doubled the actual T2DM prevalences compared to using the correct glucose cut-off points. The errors occurred due to modern glucose meters producing measurements in plasma-equivalent concentrations from whole blood samples. The incorrect whole blood glucose cut-off (≥6.1mmol/L) was applied instead of the correct plasma glucose cut-off (≥7.0mmol/L). This error likely affects other Pacific states, and may have global ramifications. © 2016 The Authors. Journal of Diabetes published by John Wiley & Sons Australia, Ltd and Ruijin Hospital, Shanghai Jiaotong University School of Medicine.