Most clinical trials on the treatment of arterial hypertension use office blood pressure measurements (Franklin et al. 2001; Hansson et al. 1998) both as inclusion criteria and study end-points. In these trials, blood pressure is taken by manual or automated devices in outpatients coming to a study center, as recommended by the European Society of Cardiology/European Society of Hypertension (ESC/ESH) Guidelines for the management of arterial hypertension (Mancia et al. 2013). The target blood pressure as recommended by European (Mancia et al. 2013) or US (James et al. 2014) guidelines largely depends on the results of the Hypertension Optimal Treatment (HOT) study (Hansson et al. 1998). This large trial with \>18.000 participants measured blood pressure with an oscillometric device three times in a row in seated patients after 5min of rest. This and similar trials form the backbone of our knowledge about what is considered normal blood pressure and what blood pressure levels should be aimed at when using antihypertensive treatment (Zanchetti et al. 2009).
Studies using 24h-blood pressure measurement devices indicated that the normal values are lower (average 10/5mmHg) with this technique than with regular office measurements (Head et al. 2010). It is well known that there is a so called "white coat" hypertension, i.e. higher blood pressure values are taken in the doctor's office than at home (Mancia et al. 1987). The amount of this white-coat effect is largely different between individuals. Although white-coat hypertension itself has some prognostic impact on the patient (Verdecchia et al. 2005) it is much less relevant than overt hypertension. It seems reasonable to keep the White coat effect in mind to avoid over-therapy in patients in whom this effect is particularly strong.
While the framework for clinical decision making is mostly based on studies using office blood pressure readings, the SPRINT study (Wright et al. 2015) recently used another way of measuring blood pressure. The SPRINT study included more than 9.300 cardiovascular high-risk individuals without diabetes mellitus. It was a randomized prospective trial with intervention aiming at a low (\<120 mmHg) vs. standard (\<140 mmHg) systolic blood pressure. The trial was stopped early because of the large benefit of the intervention on the combined cardiovascular end-point. Since publication of this study, there is a vivid scientific discussion whether the low blood pressure goal should be aimed at in different patient populations.
The SPRINT study used a unique way of determining blood pressure. Patients were left alone in a quiet room with a programmed blood-pressure reading device that took readings at intervals after 5 minutes of relaxing. Recent studies showed that the blood pressure readings taken with the SPRINT technique are relevantly lower than the readings with regular office blood pressure measurements (Wohlfahrt et al. 2016).
Patients after renal transplantation very frequently have arterial hypertension (Kasiske et al. 2004; Paoletti et al. 2009). This is in part induced by the kidney disease or effects of the transplant and the immunosuppressive therapy; thus it might be considered a form of secondary hypertension. The KDIGO guideline (KDIGO clinical practice guideline for the care of kidney transplant recipients 2009) recommends to maintain blood pressure \<130/80 mmHg in these patients. This recommendation is based on analogy to data from the general population and has not been formally proven in transplant patients. In order to determine if the SPRINT results can be extrapolated to transplant recipients as well, it is important to show the effect size of the different blood pressure measurement techniques (SPRINT vs. regular office BP) in this particular patient group.
The study intends to quantify the difference in blood pressure when read by regular ("real life") measurement or by the SPRINT procedure (primary goal).
In addition the study will describe factors that influence this difference (e.g. renal function, proteinuria, age, time since transplantation...) (secondary goals).
