Table 3.

Association of baseline parameters with rate of kidney function decline in patients with ADPKD from the DIPAK cohort (n=583), in a stepwise backward elimination analysis

Baseline Parameters	Univariable		Final Multivariable Model
	β	P Value	β	P Value
Urine-to-plasma urea ratio, per 1 U	0.74	<0.001	0.71	<0.001
Age, per 10 yr	0.12	0.22	X	X
Sex, female versus male	0.63	0.002	X	X
Systolic BP, per 10 mm Hg	−0.24	0.001	−0.18	0.02
Diastolic BP, per 10 mm Hg	−0.34	0.002	X	X
Antihypertensive therapy, yes versus no	−0.64	0.01	X	X
Diuretics, yes versus no	−0.38	0.10	X	X
eGFR, per 10 ml/min per 1.73 m2	0.13	0.004	X	X
PKD mutation
PKD1 T	−1.15	<0.001	−0.72	0.003
PKD1 NT	−0.86	0.001	−0.63	0.02
Mayo Clinic htTKV class
1B+C	−0.93	0.01	−0.69	0.07
1D+E	−2.41	<0.001	−1.83	<0.001
24-h urine volume, L	−0.05	0.73	X	X
Estimated protein intake, per 1 g/24 h	−0.01	0.02	X	X
Estimated salt intake, g/24 h	−0.99	<0.001	−0.76	0.001

Associations tested with mixed-model analysis. The first column lists all variables that were considered. Covariates contributing with a P>0.1 were excluded until a final multivariable model was reached. Urine-to-plasma urea ratio and salt intake were natural log-transformed to attain normal distribution. Reference groups are PKD2 and others (non-PKD1 mutations) combined, and Mayo Clinic htTKV class 2 and 1A combined. Protein intake was estimated in grams with the following equation: (urine urea excretion in 24 h×0.4667×0.06+[0.031×weight])×6.25 (37). Salt intake was estimated with the following equation: sodium excretion in moles×(sum of molecular mass of sodium and chloride in grams per mole). ADPKD, autosomal dominant polycystic kidney disease; DIPAK cohort, Developing Interventions to Halt Progression of Autosomal Dominant Polycystic Kidney Disease cohort; T, truncating; NT, nontruncating; htTKV, height-adjusted total kidney volume.