Nephrology referral slows the progression of chronic kidney disease, especially among patients with anaemia, diabetes mellitus, or hypoalbuminemia: A single-centre, retrospective cohort study

Background: The Kidney Disease Improving Global Outcomes guidelines recommend nephrology referral for patients with chronic kidney disease (CKD) stages 4 to 5, significant proteinuria and persistent microscopic haematuria. However, the recommendations are opinion-based and which patients with CKD benefit more from nephrology referral has not been elucidated. Methods: In this retrospective cohort study, patients referred to our nephrology outpatient clinic from April 2017 to March 2019 were included. We excluded patients considered to have an acute decline in kidney function (annual decline in estimated glomerular filtration rate [eGFR] >10 mL/min/1.73 m2). The slopes of eGFR before and after nephrology referral were estimated and compared by linear mixed effects models. Interaction between time and referral status (before or after referral) was assessed and effect modifications by the presence of diabetes, proteinuria (defined by urine dipstick protein 2+ or more), urine occult blood, hypoalbuminemia (defined by albumin levels less than 3.5 g/dL) and anaemia (defined by haemoglobin levels less than 11.0 g/dL) were evaluated. Results: The eGFR slope significantly improved from -2.05 (-2.39 to -1.72) to -0.96 (-1.36 to -0.56) mL/min/1.73 m2/year after nephrology referral (p < .001). The improvement in eGFR slope was more prominent among those with diabetes mellitus, anaemia, and hypoalbuminemia (all p-values for three-way interaction <.001 after adjustment for covariates). Further adjustments for time-dependent haemoglobin levels, the use of erythropoiesis-stimulating agents, iron supplementation, anti-hypertensives and anti-diabetic medications did not change the significance of the interactions. Conclusions: Nephrology referral slows CKD progression, especially among those with hypoalbuminemia, diabetes or anaemia. Patients with hypoalbuminemia, diabetes or anaemia might benefit more from specialized care and lifestyle modifications by nephrologists. The inclusion of anaemia and hypoalbuminemia in nephrology referral criteria should be considered