The white-coat response in ambulatory blood pressure monitoring: Elimination and attenuation

Background: The white-coat response can be identified on ambulatory blood pressure (ABP) monitoring (ABPM) and it is seen for around 2 h if the ABPM period is started in the hospital. The white-coat response to ABPM can be calculated by subtracting the 25th h ABP from the 1st h ABP; this eliminates any effect of the 24 h variation in blood pressure. Methods: In this report we have examined whether the white-coat response is due to the environment alone or partly due to the ABPM machine (study 1). We also examined whether the white-coat response found with ABPM attenuates on repeated visits (study 2). In study 1 we started ABPM at the subject's home 3 h after an initial explanation and measurement of blood pressure in the hospital (hospital blood pressure) and examined the white-coat response (measured as the 1 st h - 25th h ABP). In study 2 we performed ABPM on three occasions starting ABPM in the hospital and examined the magnitude of the white-coat response at each visit. Results: In study 1 the hospital blood pressure was significantly higher than the hourly mean blood pressure at the same time of day on the following day. There was no significant difference between the 1st and 25th hourly means or the 2nd and 26th hourly means after the monitoring had been restarted at home. In study 2, the 1st and 25th mean hourly ambulatory blood pressures showed a significant reduction in the 1st h blood pressure over the three visits whereas the 25th h blood pressure was similar. The 1st h - 25 h systolic ambulatory blood pressure was significantly reduced (P = 0.025) whereas the reduction in diastolic ambulatory blood pressure did not attain statistical significance (P = 0.182). Conclusion: The ABPM device itself does not cause the white-coat response seen on ABPM. This response appears to be related to the environment in which ABPM is commenced and can be eliminated by calculating the ABP beginning 3 h after the subject has left the hospital environment. Attenuation of this response is seen on repeated ABPM.