A Prospective UK Multicentre Study of Kidney Donors

HYPOTHESIS

In living kidney donors, reduction in GFR post-nephrectomy results in:

1. A pressure-independent increase in aortic stiffness (aPWV)
2. An increase in peripheral and central blood pressure

EXPERIMENTAL DETAILS AND DESIGN OF PROPOSED INVESTIGATION We propose a prospective, longitudinal parallel group study of 200 kidney donors and 200 controls to be recruited over two years and followed up over one year.

Subjects: The only inclusion criterion is that subjects will be scheduled for nephrectomy for the purpose of kidney donation. Subjects will be recruited from centres, chosen because of their high numbers of live donor transplants and strength in vascular research.

Controls: We will recruit a carefully matched series of control patients from the same living donor clinics at which subjects are identified, who after screening are found to be fit for donation but do not proceed to surgery.

Exclusion criteria for both subjects and controls: These will be the current nationally set exclusion criteria for donors and will include diabetes mellitus, any history of cardiovascular or pulmonary disease, evidence of hypertensive end-organ damage, LV dysfunction (EF < 40%) and atrial fibrillation.49

Primary endpoint: Change in aPWV at 12 months adjusted for mean arterial pressure and heart rate at time of measurement compared with controls.

Secondary endpoints: Change in ambulatory blood pressure, AIx, central aortic pressure and urinary ACR compared with controls.

Secondary analysis: Change in endpoints will be analysed according to baseline GFR, change in GFR, pre-donation hypertension and ethnic group.

Investigations:

The following investigations will be performed in all subjects and controls at baseline (<6 weeks pre-donation) and 1 year post-donation. Subjects and controls will undergo routine follow up by the renal team with no alteration to normal care. No restrictions will be made to the introduction of any treatment including anti-hypertensive drugs. At baseline BMI, blood pressure and heart rate will be recorded. Routine haematological and biochemical parameters including lipids will be recorded. The following additional parameters will be determined:

1. Arterial stiffness: A Sphygmocor device will be used to measure parameters including aPWV, AIx and central aortic pressure.
2. Spot urine samples will be collected for measurement of ACR.
3. Clinic blood pressure
4. 24-hour ambulatory blood pressure studies (24h ABPM)
5. Isotope GFR for kidney donors will be measured using the renal clearance of 51Cr EDTA50, in keeping with national recommendations. Kidney function in controls will be estimated using MDRD eGFR to minimise radiation exposure and cost.

STATISTICS The original recruitment target was 800 patients. Power calculations used a SD of 1.0 m/s in aPWV and 10 mm Hg in blood pressure and a sample size of 800 patients (control and donors, 400 subjects each). This gives 80% power to detect a difference of 0.22 m/s or 2.2 mm Hg for aPWV and blood pressure allowing for 9% drop out. This is a 2-sided t test at the 2.5% significance level. During the study it was apparent the original recruitment target would not be met therefore a new sample size was calculated.

New power calculations:

Using a SD of 1.0m/s in aPWV and a sample size of 400 patients (control and donors, 200 subjects each). This gives a 92% power to detect a difference of 0.4m/s for aPWV and 4mm Hg for blood pressure allowing for 15% drop out (alpha at 5%). This is a 2-sided t test at the 2.5% significance level. Following this we aimed for a sample size of 400 patients (200 controls and 200 donors) for determination of the primary outcome of PWV in both groups.