Relationship between nephrologist care and progression of chronic kidney disease

Since chronic kidney disease (CKD) affects 11% of the United States population, and its incidence is rising, experts recommend early referral to nephrologists in the hope that it may delay the onset of end-stage disease and improve survival. However, limitations in the capacity of currently practicing nephrologists may prevent widespread early referral.

To examine the relationship between disease progression and timing of nephrology referral.

We retrospectively identified 1,553 veterans at the Durham, North Carolina VA hospital between January 1998 and December 1999 who had CKD, defined as two outpatient serum creatinines > or = 1.4 mg/dL at least three months apart. Our endpoint was a composite of progression to the next CKD stage or death. We compared the time to the composite endpoint for each CKD stage and for early CKD (stages 1-3) to advanced CKD (stages 4 and 5) using a Cox proportional hazards model for two groups: those with primary care only (PCP-only) and those with primary and nephrology care (nephrology).

Ninety-two percent had hypertension, 52% diabetes, 49% coronary artery disease, and 89% proteinuria. Angiotensin-converting enzyme inhibitors and anti-lipid medications were used by 52% and 39%, respectively. The median number of days spent in each CKD stage and the proportion of each groups reaching the composite endpoint are--stage 1: 1,149 days, 68% of the PCP-only group and 73% of the nephrology group; stage 2: 1,206 days, 60% and 65%; stage 3: 1,158 days, 69% and 63%; and stage 4: 794 days, 86% and 72%. Adjusted survival curves for the composite endpoint were similar between the two groups for CKD stages 1 (HR 1.08 for nephrology versus PCP-only) and 2 (HR 1.20); however for CKD stages 3 (HR 0.80, p < 0.05) and 4 (HR 0.75, p < 0.05), the nephrology group gained 316, 215, and 120 more days of progression-free survival, respectively.

The major limitation is difficulty accounting for unmeasured bias in specialty referrals. We were unable to analyze stage 5-to-dialysis due to the small number of individuals with the outcome.

Our data suggest that an appropriate time for nephrology comanagement of patients with CKD may be stage 3; however, prospective studies are needed to clarify the role and timing of nephrology referral.