RESUMEN
INTRODUCTION: Alarm reaction to clinical blood pressure (BP) measurement, defined white-coat effect (WCE), can cause overestimation of true BP values. AIM: To assess whether ambulatory blood pressure monitoring (ABPM) can similarly affect BP values during the initial hours of recording. METHODS: In 420 ABPMs selected for a first systolic BP (SBP) reading at least 10 mmHg higher than the mean daytime SBP, we calculated mean diurnal and 24 h SBP with and without the exclusion of the two first hours of recording defined as the WCE window (WCEw). We also calculated the magnitude and duration of WCE. These analyses were also performed separately in patients off anti-hypertensive treatment (n = 156), and on treatment with and without the inclusion of beta-blockers (respectively n = 113 and 151). RESULTS: Exclusion of WCEw period reduced mean diurnal and 24 h SBP respectively from 135 ± 0.5 to 133 ± 0.5 (p < 0.01) and from 131 ± 0.5 to 130 ± 0.5 (p < 0.02). As a result the percentage of patients diagnosed as having diurnal or 24 h hypertension was reduced respectively from 48 to 40 % and from 52 to 47 %. The magnitude of WCEw was similar in both genders but the duration was longer in females (66 ± 2 vs. 56 ± 2 min, p < 0.01). Treatment with beta-blockers was associated with a shorter duration of WCE in both genders but this effect was statistically significant only in males. CONCLUSIONS: In some patients ABPM is not free from WCE. WCE may affect the overall estimation of BP profile and is longer but less blunted by beta-blockers in females than in males.