White coat hypertension and white coat effect similarities and differences

The rise in blood pressure (BP) associated with clinical visit (white coat effect) may be one basic mechanism of white coat hypertension (persistently raised clinic BP together with a normal BP outside the clinic), but the relations between white coat hypertension, white coat effect, and target organ damage have not yet been assessed on large populations. Thus, we performed 24-h noninvasive ambulatory BP monitoring and 2D-guided M-mode echocardiography in 1,333 untreated subjects with essential hypertension and 178 control normotensive subjects. White coat hypertension was defined by an average daytime ambulatory BP < 131/86 mm Hg in women and < 136/87 mm Hg in men and its prevalence was 18.9% (n = 252). The white coat effect was calculated for systolic and diastolic BP as the difference between clinic BP and average daytime ambulatory BP. Echocardiographic left ventricular mass was slightly but not significantly greater in the group with white coat hypertension than in the normotensive group (93 v 87 g/m2, P = NS), and increased in the group with ambulatory hypertension (112 g/m2, P< .01). The prevalence of white coat hypertension markedly decreased from the first to the fourth Joint National Committee V (JNC V) stage of severity of hypertension (186/559 subjects (33%) in I; 59/501 (11%) in II 7/230 (3%) in III; 0/43 (0%) in IV; P< .001). The magnitude of the white coat effect, which was greater (all P< .01) in the group with white coat hypertension (19.7/12.5 mm Hg) than in that with ambulatory hypertension (12.5/4.2 mm Hg), increased with the JNC V stage (7/4 mm Hg in I, 16/6 mm Hg in II, 23/8 mm Hg in III, 29/12 mm Hg in IV). Furthermore, the magnitude of the white coat effect did not show any association with echocardiographic LV mass, both in the group with white coat hypertension (r = −0.02/-0.06) and in that with ambulatory hypertension (r = 0.008/−0.05). We conclude that the magnitude of the white coat effect, expressed as the difference between clinic BP and daytime ambulatory BP, may not be a clinically relevant finding, failing to reflect the severity of hypertension and the degree of associated left ventricular structural changes. The actual levels of ambulatory BP, rather than the magnitude of white coat effect, should then be used to identify the subjects with normal BP outside the clinic and potentially low cardiovascular risk.