In chronic kidney disease, ambulatory blood pressure monitoring seems more accurate in predicting subsequent health events

An ambulatory blood pressure monitor (ABPM) is worn under a patient's clothing and automatically takes BP readings at repeated intervals of the day and night; this information is collected and brought to the physician's office for analysis. ABPM may help mitigate the possible effects of "white coat hypertension," in which a patient's BP artificially increases simply because of visiting a physician's office. According to background information in the article, this phenomenon is especially prevalent in CKD. Additional research suggests that nighttime BP, removed from physical, emotional and other stresses, may be a better measure of a patient's actual BP status and his or her risk for cardiovascular problems.

Roberto Minutolo, M.D., Ph.D., from the Second University of Naples in Italy, and colleagues conducted a study of patients with CKD whose blood pressure was routinely monitored at four Italian nephrology clinics. They recruited 436 participants between 2003 and 2005. Researchers measured each patient's BP three times during a morning office visit, outfitted him or her with an ABPM that took readings every 15 minutes during the day and every half hour at night, and obtained three more in-office BP readings the next day when patients returned. Participants also kept diaries of their activities, to help researchers interpret the results.

During a median followup time of 4.2 years, 86 patients experienced end-stage renal disease and 69 died; researchers also recorded 63 cardiovascular events that were not fatal and 52 deaths related to cardiovascular problems. Risk of both renal and cardiovascular outcomes was highest in participants whose daytime systolic blood pressure (SBP) was 135 mm Hg (milligrams of mercury) or above. The same risk was found for participants in the highest quintile of diastolic blood pressure (DBP), or who had nighttime SBP readings of 124 mm HG or higher. Additionally, nighttime DBP of 70 mm Hg or higher was a predictor of cardiovascular events and end-stage renal disease. "In contrast," the authors note, "office BP measurement (either SBP or DBP) did not predict cardiovascular or renal events."

The study suggests that ABPM may be a more useful tool than office BP measurements in assessing the risk that a patient with CKD will experience serious renal or cardiovascular events, and that its predictive value appears independent of other risk factors for these conditions. "Of interest, the lack of predictive value of office BP measurement, as well as office BP target level, raises concerns regarding the adequacy of recommendations of hypertension guidelines that are derived mainly from expert opinion and post hoc analyses rather than randomized trials." They conclude that "interventional studies based on ABPM rather than office BP measurement are urgently required in this high-risk population."

Commentary: Taking Blood Pressure Monitoring Out of the Office

For the 13 percent of the U.S. population who are believed to have CKD, keeping track of BP is crucial, according to a commentary accompanying the article. David Goldsmith, F.R.C.P, from King's Health Partners AHSC in London, England; and Adrian Covic, M.D., Ph.D., F.R.C.P.(Lond), F.A.S.N., from C.I. Parhon University Hospital in Iasi, Romania point out that declines in kidney function are known to increase cardiovascular risk, with BP being just one factor. "Patients with CKD die of cardiovascular disease as much as, or more often than, their disease progresses to requiring dialysis," they write. "The 'survivors' then reach dialysis, where again it is cardiovascular disease that primarily causes their demise."

The study by Minutolo and colleagues, therefore, expands the evidence in support of ABPM as an important tool for directing the care of patients with CKD. This is especially true, the authors write, given that the study demonstrated a white coat hypertension rate of 43.3 percent. While a prospective, randomized trial of ABPM as a basis for providing BP therapy for patients with CKD is needed, Goldsmith and Covic conclude, "We believe that there are selected cohorts of patients in whom the additional time, effort, and expense of doing ABPM is justified, and this new study by Minutolo and colleagues makes that case stronger for our patients with CKD. It is now harder to defend reliance on clinic BP measurement alone if we nephrologists are serious about targeted BP intervention."