Estimation of Urinary Marinobufagenin in Stable Chronic Kidney Disease Patients: A Hospital-based Cross-sectional Study.

Background

Chronic kidney disease (CKD) is associated with accumulation of endogenous cardiotonic steroids, including marinobufagenin (MBG), a bufadienolide that inhibits Na+/K+-ATPase and promotes renal and cardiac fibrosis. Urinary MBG (uMBG) excretion reflects glomerular filtration and may decline as renal function deteriorates, yet data from Indian populations are lacking.

Objectives

To estimate uMBG levels in stable CKD patients (kidney disease improving global outcomes stages 2-4), to correlate these levels with markers of renal function and CKD severity, and to assess the diagnostic utility of uMBG as a biomarker.

Methods

A hospital-based cross-sectional study was conducted in department of medicine King George's Medical University, Lucknow over a period of 1 year. Seventy stable CKD patients (stages 2-4) and 25 age-and sex-matched healthy controls were enrolled. uMBG was estimated by competitive enzyme-linked immunosorbent assay method.

Results

uMBG was significantly lower in CKD patients compared to controls (median 6.85 [interquartile range 4.95-8.59] vs. 11.78 [10.61-12.3] pg/mL; P < 0.001). A highly significant inverse gradient was observed across CKD stages 2-4 (Kruskal-Wallis H = 60.698; P < 0.001; Kendall's τ = -0.826; P < 0.001). Estimated glomerular filtration rate was the dominant correlate of uMBG (ρ = 0.976; P < 0.001) and the sole independent predictor on multivariate regression (β = 0.00708; P < 0.001; R2 = 0.672). Receiver operating characteristic analysis yielded an area under the curve (AUC) of 0.914 with sensitivity 82.6% and specificity 100% at a cut-off of 9.3 pg/mL.

Conclusion

uMBG is significantly reduced in stable CKD and declines progressively with advancing disease stage, mirroring the decline in glomerular filtration rate. uMBG has the ability to be a novel, stage-sensitive biomarker for CKD due to its excellent diagnostic accuracy (AUC 0.914).