Ambulatory blood pressure monitoring in children with a solitary kidney - a comparison between unilateral renal agenesis and uninephrectomy.

BACKGROUND: In experimental animals, a reduction in renal mass leads to glomerulosclerosis of the residual parenchyma and eventual renal failure. In humans, however, data on the influence of nephrectomy or agenesis on future functional parameters and hypertension are as yet controversial.

OBJECTIVE: To evaluate blood-pressure patterns in children with a solitary kidney as a result of either unilateral renal agenesis (URA) or uninephrectomy (UNX) and correlate them to the increase in size of the remaining kidney.

METHODS: Twenty-eight children with a solitary kidney were divided into two groups: the URA group, with 18 subjects (13 male and five female, with a mean age of 9.6 +/- 3.9 years), and the UNX group, which contained 10 subjects (four male and six female, with a mean age of 14.0 +/- 2.7 years). The mean time since nephrectomy was 8.7 years. Each study group was assigned an age-, weight- and height-matched control group. In all subjects, ambulatory blood pressure monitoring was performed using the SpaceLabs model no. 90207. Daytime and night-time were defined as 0800-2200 h and 2200-0800 h, respectively. Urinalysis, serum creatinine and urea results were recorded for all the study group participants. The size of the remaining kidney was determined by ultrasound examination. The percentage increase in kidney size, as calculated from standard kidney-length-against-age nomograms was correlated to the percentage deviation from normal blood pressure values.

RESULTS: The mean 24 h, daytime and night-time systolic blood pressure (SBP) readings were significantly higher in children in the URA group than in those in the corresponding control group (111.4 +/- 7.5 mmHg versus 106.9 +/- 6.7 mmHg, P < 0.004; 115.2 +/- 3.1 mmHg versus 110.7 +/- 3.4 mmHg, P < 0.004; and 105.2 +/- 2.6 mmHg versus 101.2 +/- 1.8 mmHg, P < 0.002, respectively). Daytime heart rate was found to be significantly reduced (84.4 +/- 5.2 versus 87.8 +/- 8.2 beats/min, P < 0.04). In the UNX group, 24 h mean, systolic and diastolic blood pressure (DBP), as well as heart rate, did not differ from control values. Daytime systolic and diastolic blood pressures were higher than those of the controls (119.8 +/- 4.0 mmHg versus 115.5 +/- 3.8 mmHg, P < 0.02; and 72.7 +/- 4.0 mmHg versus 70.0 +/- 11.0 mmHg, P < 0.02, respectively). Nocturnal dipping was present in all groups and was of equal magnitude in the corresponding control groups. The mean 24 h diastolic blood pressure load was significantly greater in URA patients than in controls (19.6 versus 10.8%, respectively, P < 0.01). In the UNX group, the blood pressure loads were similar to those of controls. The percentage increase in length of the remaining kidney was found to correlate positively with the percentage delta increase in both systolic and diastolic blood pressure.

CONCLUSIONS: Compared with the age-, height- and weight-matched controls, the children with a solitary kidney caused by URA had an elevated mean 24 h SBP. In contrast, those with UNX had mean 24 h blood pressure values similar to those of their controls. A rise in SBP was, however, seen in both groups during the daytime hours. Thus, the presence of a solitary kidney, for whatever reason, may be pathogenetically linked to a raised blood pressure, and this linkage may be more pronounced in URA. The delta increase in size of the remaining kidney may serve as a prognostic indicator of blood pressure elevation.