RESUMEN
BACKGROUND: In a cluster-randomized trial including 1832 hypertensive patients, all 126 general practitioners (GPs) in the intervention group (IG) used an oscillometric device that was provided for blood pressure (BP) measurements. Of the 131 GPs of the control group (CG), 24.6% used an oscillometric device (OCG), and 75.4% used a manual device (MCG). At baseline, patients in the IG and CG were comparable for all clinical and biological characteristics, except BP, which was higher in the IG (146/84 vs. 139/81 mmHg; P<0.001). The purpose of this ancillary study was to assess whether these differences in BP values were related to the end-digit preference (EDP), selection bias, or both. METHODS: Analysis was carried out and comparison was made of 3629 BP measurements by 257 GPs. Statistical analysis used hierarchical mixed-effect models with random physician effect and fixed-effect covariables. RESULTS: The frequencies of 0 end digit were 16.7% in the IG, 32.4% in the OCG and 68.8% in the MCG for systolic BP (SBP; P<0.001 for all comparisons), and respectively 17.7, 38.1, and 74.1% for diastolic BP (DBP; P=0.017 for all comparisons). SBP was higher in the IG than in OCG (+3.65 mmHg, P=0.017). The same trend was observed for DBP, though not significant (+1.50 mmHg, P=0.20). The EDP in the CG led to a mean underevaluation of 2.4 mmHg (P<0.0005) of SBP and DBP. CONCLUSION: The observed differences in BP between the groups are partly explained by the impact of EDP. Compared with the manual, oscillometric measurement may reduce EDP.
