Nephrology Referral Based on Laboratory Values, Kidney Failure Risk, or Both: A Study Using Veterans Affairs Health System Data

Abstract

Rationale & objective: Current guidelines for nephrology referral are based on laboratory criteria. We sought to evaluate whether nephrology referral patterns reflect current clinical practice guidelines and to estimate the change in referral volume if they were based on the estimated risk of kidney failure.

Study design: Observational cohort.

Setting & participants: Retrospective study of 399,644 veterans with chronic kidney disease (October 1, 2015 through September 30, 2016).

Exposure: Laboratory referral criteria based on Veterans Affairs/Department of Defense guidelines, categories of predicted risk for kidney failure using the Kidney Failure Risk Equation, and the combination of laboratory referral criteria and predicted risk.

Outcome: Number of patients identified for referral.

Analytical approach: We evaluated the number of patients who were referred and their predicted 2-year risk for kidney failure. For each exposure, we estimated the number of patients who would be identified for referral.

Results: There were 66,276 patients who met laboratory indications for referral. Among these patients, 11,752 (17.7%) were referred to nephrology in the following year. The median 2-year predicted risk of kidney failure was 1.5% (interquartile range, 0.3%-4.7%) among all patients meeting the laboratory referral criteria. If referrals were restricted to patients with a predicted risk of ≥1% in addition to laboratory indications, the potential referral volume would be reduced from 66,276 to 38,229 patients. If referrals were based on predicted risk alone, a 2-year risk threshold of 1% or higher would identify a similar number of patients (72,948) as laboratory-based criteria with median predicted risk of 2.3% (interquartile range, 1.4%-4.6%).

Limitations: Missing proteinuria measurements.

Conclusions: The current laboratory-based guidelines for nephrology referral identify patients who are, on average, at low risk for progression, most of whom are not referred. As an alternative, referral based on a 2-year kidney failure risk exceeding 1% would identify a similar number of patients but with a higher median risk of kidney failure.

Keywords: CKD progression; Chronic kidney disease (CKD); clinical epidemiology; health services; kidney failure risk; nephrology referral; prognosis; referral volume; risk prediction.

Figure 1.

Cohort flow diagram. Comprises 399,644 veterans with CKD stages 3 or 4 (by eGFR) and regular visits to a VA primary care physician who were not under hospice care. The pathway on the left describes cohort selection for all patients with laboratory-based indications for nephrology referral. The pathway on the right describes cohort selection for all patients with CKD, regardless of whether they met an indication for referral. Abbreviations: CKD, chronic kidney disease; eGFR, estimated glomerular filtration rate; VA, Veterans Affairs.

Figure 2.

Projected annual referral volumes using laboratory indications and kidney failure risk. The dotted line indicates the number of patients meeting Veterans Affairs/Department of Defense laboratory indications for referral. The dark circles indicate the projected number of patients meeting 2-year predicted risk of kidney failure thresholds ranging from 1% to 10%. The lighter circles indicate the projected number of patients meeting both laboratory indications for referral and kidney failure risk thresholds. Projections are extrapolated from patients with available urine albumin or urine protein measurements. Abbreviation: KFRE, Kidney Failure Risk Equation.