Seasonal variation in outpatient blood pressure in stable renal transplant recipients

Seasonal variation in blood pressure (BP) has been described in the general and dialysis populations, with higher recordings noted in the winter than in the summer. This difference has been attributed to changes in weight, ambient temperature, and length of daylight. In this study, we sought to determine whether such seasonal differences exist in renal transplant recipients, a group with a high prevalence of hypertension. We reviewed our outpatient population of 652 adult renal transplant recipients and identified primary allograft recipients with graft survival >1 year, stable renal function, on both cyclosporine and prednisone, and who had >1 pair of post-first year "winter" (defined as the months of January and February) plus "summer" (defined as the months of July and August) outpatient BP measurements from the same year. One hundred sixty-three patients met entry criteria, from whom 432 BP pairs were obtained. When the most recent pair from each patient was analyzed (n=163), diastolic and mean BP were found to be higher in winter than summer (by 2.5 and 2.3 mmHg, respectively, P<0.01 for each) by a paired Student t test. In a separate analysis using all BP pairs (n=432), systolic, diastolic, and mean BP were found to be significantly higher in winter (by 5.3, 2.7, and 3.5 mmHg, respectively, P<0.001 for each). An effect of season was confirmed in a multiple regression model of common predictors for hypertension, controlling for number of BP pairs per patient. In conclusion, renal transplant recipients demonstrate higher BP in the winter than in the summer. This effect is independent of known predictors of hypertension in this population and may be, at least, partly related to changes in length of daylight and temperature.