Poor agreement between dialysis unit blood pressure and interdialytic ambulatory blood pressure

Although ambulatory blood pressure (ABP) monitoring (ABPM) is often considered to have an advantage over dialysis unit blood pressure (BP) in dialysis patients, the exact relationship between these two measurements of BP has not been well determined. In a cohort of 90 Chinese dialysis patients, agreement between dialysis unit BP (predialysis and postdialysis BP) and interdialytic ABP was evaluated using Bland-Altman plots and Lin's concordance correlation coefficient for quantitative analysis, and inter-rater agreement (κ) for qualitative analysis. Limits of agreement between dialysis unit BP and ABP were wide (predialysis systolic BP: -33.5 to 20.9 mm Hg; predialysis diastolic BP: -22.2 to 11.9 mm Hg; postdialysis systolic BP: -25.4 to 26.5 mm Hg; postdialysis diastolic BP: -18.4 to 12.3 mm Hg). Lin's concordance correlation coefficient exhibited a poor agreement with concordance correlation coefficients of 0.75, 0.81, 0.64, and 0.75 for predialysis systolic BP, postdialysis systolic BP, predialysis diastolic BP, and postdialysis diastolic BP, respectively. When BP level was classified into quartiles, an increasing trend for incorrect classification rate was observed with deleterious hypertension, with the highest value in grade 3 hypertension (100% and 75.0% for predialysis and postdialysis BP, respectively). Therefore, these data suggest that agreement between dialysis unit BP and interdialytic ABP is poor in Chinese dialysis patients, and the bias for patients with higher degree of hypertension is more prominent.