Measurements
The exposure of interest, daily sodium intake, was estimated by measuring
24-hour urinary sodium excretion. To correct for body size
and possible collection errors, urinary sodium excretion was normalized
to urinary creatinine excretion by calculating the sodium/
creatinine ratio from24-hour urine samples (sodium/creatinine ratio,
mEq/g).39 Urinary urea and protein excretion were normalized to
urinary creatinine excretion, as well. BP was measured at randomization
and every 3 months thereafter. Creatinine clearance, 24-hour
urinary protein, and sodium and urea excretion were measured at
randomization, at 3 and 6 months after randomization, and every
6 months thereafter. Baseline data were taken when all participants
had completed the 6-week wash-out period from previous ACE inhibitor
therapy, that is, at randomization for patients from the REIN trial
and at the inclusion visit for those from the REIN-2 trial. Thus, all
baseline data were without ACE inhibition and all outcome data were
with ramipril (5 mg/d) therapy.