Serum β2-microglobulin, cystatin-C, and urinary KIM-1 as predictors of early renal impairment in women with diabetes in pregnancy: a prospective cohort study.

BACKGROUND

Diabetes in pregnancy (DIP), including pregestational diabetes mellitus (PGDM) and gestational diabetes mellitus (GDM), increases the risk of early renal impairment. However, conventional renal markers are often insensitive in the early stages. Emerging biomarkers—serum β2-microglobulin (β2-MG), Cystatin-C (CysC), and urinary kidney injury molecule-1 (KIM-1)—may enhance early detection. This study aimed to evaluate the diagnostic and predictive value of β2-MG, CysC, and KIM-1 for early renal impairment in women with DIP using longitudinal, survival, and mediation analyses.

METHODS

In this prospective cohort study, 360 women with DIP were followed at four visits: mid-pregnancy, late pregnancy, delivery, and 6 months postpartum. Serum β2-MG, CysC, and urinary KIM-1 were measured longitudinally. Early renal impairment was defined as a urinary albumin-to-creatinine ratio (UACR) ≥ 30 mg/g or a ≥ 10% decline in estimated glomerular filtration rate (eGFR). Logistic regression, receiver operating characteristic analyses, time-dependent Cox proportional hazards models, and mediation analyses were conducted to evaluate predictive performance and potential pathways.

RESULTS

Seventy-two women (20.0%) developed early renal impairment. Baseline levels of β2-MG (2.41 ± 0.35 vs. 1.82 ± 0.29 mg/L), CysC (1.05 ± 0.15 vs. 0.85 ± 0.12 mg/L), and KIM-1 (3.42 ± 0.71 vs. 1.91 ± 0.52 ng/mg Cr) were significantly higher in affected participants (all P < 0.001). All three biomarkers independently predicted renal impairment (adjusted odds ratios: β2-MG 2.15; CysC 1.92; KIM-1 2.78). A combined model incorporating clinical variables and all biomarkers achieved the highest discrimination (AUC = 0.90; sensitivity 83.3%; specificity 81.9%). In time-dependent Cox analyses, elevated biomarker levels were associated with earlier onset of renal impairment (adjusted hazard ratios: β2-MG 1.87; CysC 1.72; KIM-1 2.41). Biomarkers mediated 24–34% of the association between glycated hemoglobin (HbA1c) and renal impairment. Longitudinal trajectories showed progressive increases during pregnancy, peaking at delivery and partially declining postpartum, with individuals exhibiting persistently high levels remaining at elevated risk.

CONCLUSIONS

Serum β2-MG, CysC, and urinary KIM-1 are independent predictors of early renal impairment in women with DIP. Their combined assessment substantially improves early risk stratification beyond conventional renal markers. CLINICAL TRIAL NUMBER: Not applicable.