|Year : 2020 | Volume
| Issue : 6 | Page : 1254-1262
|Significance of ambulatory blood pressure monitoring in assessment of potential living kidney donors
Niamh M Brady1, Hatem Ali2, Fiona Biggins3, Aimun Ahmed4
1 Department of Renal Medicine, Royal Preston Hospital, Lancashire Teaching Hospitals NHS Foundation Trust, Preston; Department of Renal Medicine, Medical School, University of Manchester, Manchester, UK
2 Department of Renal Medicine, University Hospitals of Coventry and Warwickshire, NHS Foundation Trust, Coventry, UK
3 Department of Renal Medicine, Royal Preston Hospital, Lancashire Teaching Hospitals NHS Foundation Trust, Preston, UK
4 Department of Renal Medicine, Royal Preston Hospital, Lancashire Teaching Hospitals NHS Foundation Trust, Preston; Department of Renal Medicine, Medical School, University of Manchester, Manchester, UK; Department of Nephrology, Faculty of Medicine, Ain Shams University, Cairo, Egypt
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|Date of Web Publication||29-Jan-2021|
| Abstract|| |
The most recent British Transplant Society (BTS) guidelines recommend that office blood pressure (BP) monitoring in living donors is sufficient for the assessment of hypertension (HTN) and those with BP >140/90 should be further assessed using ambulatory BP monitoring (ABPM). ABPM can detect diurnal and nocturnal variation in BP, thus it can identify masked HTN. The aim of the current study is to assess reliability of ABPM vesus office BP monitoring for assessment in living kidney donors. Office and ABPM of all potential kidney donors at a single center from April 2009 to March 2017 were retrospectively reviewed and compared. Age, sex, body mass index, kidney function, and echocardiography results were collected and analyzed. Two hundred and sixteen kidney donors were stratified based on their BP readings into four groups; group 1 (masked HTN: normotensive in office and hypertensive in ABPM), group 2 (sustained normotension: normotensive in office and in ABPM), group 3 (sustained HTN: hypertensive in office and in ABPM), group 4 (white-coat HTN: hypertensive in office and normotensive in ABPM). Thirteen percent of patients were diagnosed with masked HTN. Office systolic BP monitoring was significantly higher in patients older than 50 years old compared to other younger populations. However, this significant difference in systolic BP was diminished when assessment with ABPM was performed. In conclusion, ABPM is a reliable modality for the identification of masked HTN and white coat HTN. Masked HTN is correlated with increased risk of end organ damage and risk of death in potential kidney donors. Transplant physicians cannot rely solely on office BP monitoring in the assessment of potential living kidney donors. ABPM should be integral part of routine assessment of potential living kidney donors.
|How to cite this article:|
Brady NM, Ali H, Biggins F, Ahmed A. Significance of ambulatory blood pressure monitoring in assessment of potential living kidney donors. Saudi J Kidney Dis Transpl 2020;31:1254-62
|How to cite this URL:|
Brady NM, Ali H, Biggins F, Ahmed A. Significance of ambulatory blood pressure monitoring in assessment of potential living kidney donors. Saudi J Kidney Dis Transpl [serial online] 2020 [cited 2021 Apr 21];31:1254-62. Available from: https://www.sjkdt.org/text.asp?2020/31/6/1254/308334
| Introduction|| |
Renal transplantation is the preferred option for most of patients with end-stage renal failure as it provides better quality of life and lower mortality rates when compared to dialysis.,
Living kidney donation has better graft and patient survival compared to deceased kidney donation, it can be a growing source in the shortage of deceased donor rates to meet increasing numbers of patients on the list waiting for kidneys. Nonetheless, living renal donation requires that a healthy volunteer undergoes complex surgical operation without any health benefit in return. Despite being scarce, perioperative death can happen during nephrectomy in living donors and have been postulated to happen in <0.03% of renal donors., Kidney donation undeniably can cause decreased renal function, post donation there is a small risk of developing proteinuria and an increase in blood pressure (BP) more than that determinable to natural aging. For every 10 mm Hg rise in systolic BP, there is 1.5 increased risk of death due to increased cardiovascular risk or stroke and donors might have a 5–10 mm Hg rise in BP compared to other population of similar age at 10 years follow-up. Recent studies showed overall increase in all-cause mortality and cardiovascular risk over 15 years in addition to possible increased risk of pre-eclampsia in female donors., Hypertension (HTN) is one of the most common causes for exclusion from living kidney donation.,
The current British transplant society (BTS) guidelines recommend that office BP monitoring in living donors is sufficient for the assessment of HTN and those with BP >140/90 should be further assessed by ambulatory BP monitoring (ABPM). End-organ damage and left ventricular hypertrophy have been correlated with night time HTN (non dipping of BP) and diurnal variation in BP, hence the term of masked HTN has arisen. To the contrary, patients with white coat HTN have no increased risk of cardiovascular events compared to the general population.
ABPM can detect diurnal and nocturnal variation in BP, thus, it can identify masked HTN and white coat HTN. Many studies showed that results of ABPM are better correlated with adverse cardiovascular outcomes and risk of death.,, Many studies showed that masked HTN is prevalent in chronic kidney disease (CKD) population and is closely correlated with decrease on glomerular filtration rate (GFR) and proteinuria. The aim of the current study is to assess the reliability of ABPM versus office BP monitoring for the assessment of HTN in potential kidney donors and to highlight the importance of using ABPM monitoring in this population.
| Patients and Methods|| |
Office and ABPM of all potential kidney donors at a single center from January 2009 to January 2017were retrospectively reviewed. Office BP measurements were recorded during initial clinic visits, as part of initial donor work-up. Potential kidney donors who were known to be hypertensive, on antihypertensive medications or those who failed to have subsequent ABPM were excluded from the study. Office BP readings were classified as hypertensive if >140/90 mm Hg, whereas mean 24-h BP was classified as hypertensive if >125/80 mm Hg, as in line with the 2011 BTS kidney donor guidelines. Living donors who had both office BP and ABPM were included. Data about age, sex, body mass index, estimated GFR, urine protein to creatinine ratio, echocardiography results and fasting glucose/oral glucose tolerance test results were collected. All potential donors were initially evaluated by transplant nurse co-ordinator and those who potentially did not have contraindication to donation were referred to transplant physician for further evaluation. BP measurements were done one or two times in the clinic in quiet setting using automated BP machine. The average of two measurements was denoted as clinic or office BP. ABPM monitoring was performed using specialized automated machines that measure BP every 20 min during the day and every 30 min overnight. Time of awakening and time of sleep were self-reported by the patients.
| Statistical Analysis|| |
Statistical analysis was performed using Excel 15.23.1. Correlation was performed using linear regression analysis to look at the relationship between office and ambulatory BP readings; subsequent Bland-Altman plots were made, which plotted the differences between and the means of office and ambulatory BP readings to further ascertain the level of agreement of the two methods. Unpaired t-tests assuming unequal variance were performed comparing average BP of the different BP groups and age groups, as well as parameters of the different groups.
| Results|| |
Two hundred and sixteen potential kidney donors (females = 120, males = 96) were included in the study. Most of the individuals involved were European in ethnicity. The cohort population were stratified based on their BP readings into four groups; Group 1 (masked HTN: normotensive in office BP monitoring and hypertensive in ABPM), Group 2 (sustained normotension: normotensive in office BP monitoring and in ABPM), Group 3 (sustained HTN: hypertensive in office BP monitoring and in ABPM), Group 4 (white coat HTN: hypertensive in office BP monitoring and normotensive in ABPM). Baseline characteristics of all four groups are shown in [Table 1].
[Figure 1] shows a graph of office systolic BP versus mean 24-h systolic BP and the classification of each systolic BP measurement as hypertensive or not, and subsequent subdivision into normotensive, white-coat HTN, masked HTN, or sustained HTN. Office systolic BP and mean 24-h systolic BP were correlated with r = 0.363, P < 0.001.
|Figure 1: Plot of office systolic blood pressure versus mean 24-h systolic blood pressure.|
Scatter plot of data from office systolic blood pressure and mean 24-h systolic blood pressure from 216 prospective kidney donors analyzed on Excel. Correlation r = 0.363 (P <0.01).
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[Figure 2] shows a graph of office diastolic BP versus mean 24-h diastolic BP and the classification of each diastolic BP measurement as hypertensive or not, and thus subsequent subdivision into one of four groups. Office and mean 24-h diastolic BP were correlated with r = 0.271, P <0.05.
|Figure 2: Plot of office diastolic blood pressure versus mean 24-h diastolic blood pressure.|
Scatter plot of data from clinic diastolic blood pressure and mean 24-h diastolic blood pressure from 216 prospective kidney donors analyzed on Excel. Correlation r = 0.271 (P <0.01).
Click here to view
Analysis of the two BP measures (office BP and ABPM) was performed using Bland-Altman plots, for both systolic and diastolic BP, which plots the mean of the two measures against the difference between the two measures. [Figure 3] shows the means of systolic measures versus the differences between office and ambulatory 24-h systolic BP. [Figure 4] shows the means of diastolic measures versus the differences between office and ambulatory 24-h diastolic BP. The mean of the differences between office and average 24-h systolic BP, or the bias, was 20.52. The upper limit of agreement was 53.60 and the lower limit of agreement was -12.57. Linear regression analysis on the plot showed a slope of 0.393 of the best fit line (P <0.001, R2 = 0.08). The mean of the difference between office and average 24-h diastolic BP was 12.33. The upper limit of agreement was 53.60 and the lower limit of agreement was 53.60. Linear regression analysis on the plot showed a slope of 0.554 (P <0.001, R2 = 0.13).
|Figure 3: Plot of mean systolic measures versus differences between systolic measures|
Plot of mean systolic measures (clinic systolic BP and 24-h ambulatory BP) versus differences between systolic measures from 216 prospective kidney donors analysed on Excel. Bias = 20.52. Lower limit of agreement = -12.57, Upper limit of agreement = 53.60. Correlation r = 0.283 (P <0.01). Slope = 0.393 (P <0.01).
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|Figure 4: Plot of mean diastolic measures vs. differences between diastolic measures|
Plot of mean systolic measures (clinic systolic BP and 24-h ambulatory BP) vs. differences between systolic measures from 216 prospective kidney donors analyzed on Excel. Bias = 12.33. Lower limit of agreement = -11.25, Upper limit of agreement = 35.91. Correlation r = 0.359 (P <0.01). Slope = 0.554 (P <0.01).
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There were data on echocardiography and left ventricular function available for 168 donors; most of the donors’ echocardiograms were normal except for two donors with sustained normotension, three donors with white-coat HTN, seven donors with sustained HTN, and one donor with masked HTN. These donors exhibited varying degrees of end-organ damage: features of the echocardiograms of donors in the sustained HTN group included a septal bulge, mild diastolic dysfunction, dilated left atrium, “aneurysmal,” left ventricular hypertrophy, mild concentric left ventricular hypertrophy, and incomplete right bundle branch block. Features of the white coat HTN group included mild mitral regurgitation and mild diastolic dysfunction. Features of the sustained normotension group included trivial mitral regurgitation and atrial regurgitation, and a trace of tricuspid regurgitation. The one donor of the masked HTN group who had an abnormal echocardiogram had mild left ventricular hypertrophy.
Donors were also categorized into groups based on age. Group A included donors ≤35 years old (n = 46), Group B included donors between 36 and 29 years (n = 61), and Group C included donors ≥50 years old (n = 109). Characteristics of these groups are shown in [Table 2].
| Discussion|| |
Living kidney donation necessitates that healthy candidates endure complex surgery without any health interest in return. Despite scarce, perioperative deaths happen during nephrectomy from the donors at almost 0.03% of kidney donors. Donor nephrectomy is associated with decreased GFR and may lead to rise in proteinuria, in addition to an increase in BP more than that traceable to natural aging. These elements are conjoined with higher risk for cardiovascular deaths in the general population. Minimal changes in BP, particularly, can lead to significant rise in cardiovascular risk and thereby risk of mortality. This peculiar relationship between HTN and increased cardiovascular risk has lead HTN to be one of the most common causes of exclusion from donation. Exclusion of potential donors with uncontrolled HTN has led to scarcity of data about impact of HTN on long-term outcomes of kidney donation.
Many studies have proved that ABPM is a superior modality of prediction of target organ damage and long-term outcomes compared to office BP monitoring.,, However, few studies assessed HTN in potential kidney donors using this modality. In 2000, Özdemir et al compared ABPM to office BP monitoring in 126 living related kidney donor and proved superiority of ABPM in detecting HTN. All of the individuals involved in their study were relatives of patients with end-stage renal failure and this raise susceptibility of potential genetic and environmental factors predisposing them to HTN and end organ damage. In 2003, Textor et al showed similar results when compared ABPM to office BP monitoring on Caucasian population. Similarly, in 2007, Ommen et al. showed that ABPM is better than office BP monitoring in the assessment of HTN in potential kidney donors. However, 30% of the cohort were African population and 30% were Hispanic and this could have led to bias of the results as African population has higher prevalence of HTN and Hispanic population has lower prevalence. Our study is the first study to assess benefit of ABPM among the European population. Our results coincided with that of previous results that ABPM is superior to office BP monitoring in potential kidney donor population. In our study, 13% of patients were diagnosed as masked HTN. This is different from previous studies where masked HTN were diagnosed in only 7% in Özdemir et al study and 17% in Ommen et al study. These differences could be related to different ethnic groups included in these studies and, also could be related to the lack of consistency in defining HTN. In our study, we used BTS guidelines in setting cut-off measurements for diagnosing HTN.
BTS has recommended that office BP monitoring is sufficient for the assessment of HTN in potential kidney donors and that individuals diagnosed with hypertensive should be referred for further assessment using ABPM. The result of our study, however found that relying on office BP monitoring alone could lead to missing up to 13% of patients with undiagnosed HTN. With lack of resources in many health-care systems, using ABPM routinely in the assessment of potential kidney transplant donors would lead to more burden on expenses. However, on the other hand, potential kidney donors with undiagnosed HTN are more prone to worse cardiovascular and renal outcome post-nephrectomy and thereby these patients will exert more burden on healthcare systems. This burden could be prevented by early identification of this risk using ABPM.
Several studies confirmed that masked HTN is an absolute risk factor for target organ damage.,, In 2014, Minutolo et al confirmed in a multi-center study that included more than 480 patients with CKDs that masked HTN is a strong predictor of increased cardiovascular risks. In a recent study by Drawz et al that were performed on more than 1400 patients with CKD, authors found that masked HTN was associated with higher left ventricular mass index and pulse wave velocity. Both of these entities were associated with higher risk of all-cause mortality. In Drawz et al. study, night time HTN was associated with lower GFR and more proteinuria. Therefore, authors high-lighted that ABPM is more important than home BP monitoring in the assessment of HTN and end-organ damage.
We found that office systolic BP monitoring was significantly higher in patients older than 50 years old compared to other younger populations. However, this significant difference in systolic BP was diminished when assessment with ABPM was performed. This reflects that older patients are more prone to have white coat HTN. Nevertheless, white-coat HTN is not free of risk. Several studies showed that white coat HTN is a significant risk factor for developing end-organ damage compared to sustained normotension, although this risk is less compared to sustained HTN.,, In Japan, a large study found that the risk of developing sustained HTN at 10 years follow-up was higher among patients with white-coat HTN compared to those with sustained HTN. In Ommen et al study, ABPM was slightly higher in patients with white coat HTN compared to those with sustained normotension. Results of our study coincided with Ommen et al. study when comparing ABPM in patients with white coat HTN and patients with sustained normotension. The major limitation of our study was its retrospective design and relatively small number of patients. Further work is needed to ascertain the effect of white coat HTN and masked HTN in living kidney donors on renal and cardiovascular outcome in this population.
In conclusion, ABPM is a reliable modality for identification of masked HTN and white coat HTN. Masked HTN is correlated with increased risk of end-organ damage and risk of death in potential kidney donors. Transplant physicians cannot rely solely on office BP monitoring in the assessment of potential living kidney donors. ABPM should be integral part of routine assessment of potential living kidney donors. More studies with larger sample size are needed to confirm these results.
Conflict of interest: None declared.
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Department of Renal, Royal Preston Hospital, Lancashire Teaching Hospitals NHS Foundation Trust, Preston
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]
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