With interest we read the article of Martin et al,1 that discussed the use of ambulatory blood pressure monitoring to better understand the clinical significance of inter-arm differences in blood pressure. We agree it is important to evaluate the diagnostic possibilities for hypertension, especially since it was shown that only half of the time GPs adhere to the guideline of subsequent blood pressure measurements.2
The authors state that the ‘white-coat’ effect is probably responsible for the inter-arm differences found in office readings. However, we have some concerns regarding this conclusion. First, a definition of the ‘white-coat’ effect is not provided by the authors. This is essential for understanding the conclusions drawn in this article. Second, the authors included both patients with a new diagnosis of hypertension as well as patients with already existing hypertension but with failure of treatment, drug intolerance, and/or in need of further investigation of underlying causes. Nevertheless, in the data analysis, these two groups were taken together. We think it is necessary to analyse these groups separately, because Pickering et al3 described a diminishing effect of antihypertensive medication on the ‘white-coat’ effect. This may also have an effect on the inter-arm differences in blood pressure in the patients with already existing hypertension. This difference even depends on which antihypertensive medication the patient is taking.3 However no information on the patients’ medication was reported. Furthermore, daytime activities have an effect on ambulatory blood pressure measurements. No information was provided as to whether the patients received instructions on how to spend their day while being monitored.
The authors collected quite some risk factors that are interesting in the context of hypertension. However, the authors did not analyse if any of these factors affected the outcome. If this was the case, it is relevant to correct for these factors in the analysis of the data.
In the results section, information is lacking on whether the first blood pressure was always the highest. If not, this could contradict the authors’ explanation of the ‘white-coat’ effect.
Finally, Figure 2 contains a Bland-Altman plot in which the ‘no-difference’ line is above zero. Is this a mistake or is there a reason?
REFERENCES
- 1.Martin U, Holder R, Hodgkinson J, McManus R. Inter-arm blood pressure differences compared with ambulatory monitoring: a manifestation of the ‘white-coat’ effect? Br J Gen Pract. 2013 doi: 10.3399/bjgp13X663055. [DOI] [PMC free article] [PubMed] [Google Scholar]
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- 3.Pickering TG, Gerin W, Schwartz AR. What is the white-coat effect and how should it be measured? Blood Press Monit. 2002;7(6):293–300. doi: 10.1097/00126097-200212000-00001. [DOI] [PubMed] [Google Scholar]