Urinary Interleukin-6 Outperforms Albuminuria for Early Detection and Treatment Response in Diabetic Kidney Disease: First Multicenter Cohort from Karbala, Iraq (n = 840).

Background: Thirty percent of diabetic kidney disease (DKD) cases lack overt albuminuria, delaying diagnosis. We examined whether urinary interleukin‑6 (uIL‑6) identifies DKD and predicts Dapagliflozin response in proteinuric and non-proteinuric phenotypes.

Methods: We conducted a multicenter prospective cohort in Karbala (one endocrinology and two nephrology centers) from July 2021 to December 2024 (42-month follow-up). Adults (≥18) with T2D and early DKD (KDIGO G1–G3) initiated dapagliflozin 10 mg daily; exclusions were non-DKD, active infection, malignancy, pregnancy, and prior SGLT2-inhibitor use. Visits were at baseline and three months; a forty-two-month subset was analyzed. Participants without follow-up were excluded; statistical weighting and data imputation addressed attrition. Midstream spot urine was processed within 1 hour, aliquoted, stored at −80 °C, with a single freeze–thaw permitted; samples with hematuria/pyuria were excluded. Urinary IL-6 was measured in duplicate by sandwich ELISA (Quantikine HS, R&D Systems; analytical range 2–600 ng/L; LOD 1.0 ng/L; intra-/inter-assay CVs <8%/<10%) ;(values <LOD were imputed as LOD/√2; sensitivity analyses indexed uIL-6 to urine creatinine. UACR (mg/g) was assayed on the same specimens; dilution bias was reduced using creatinine and, when available, specific-gravity indexing. A diabetes control cohort was used for ROC analyses. Primary outcomes were ≥20% UACR reduction (P-DKD) and ≥30% uIL-6 reduction (NP-DKD). Statistics: continuous data are mean ±SD or median (IQR); paired t or Wilcoxon as appropriate; Benjamini–Hochberg FDR (q<0.10); multivariable logistic regression for responder status (covariates: age, sex, diabetes duration, BMI, SBP, HbA1c, eGFR, UACR); AUROC with 95% bootstrap CIs, Hosmer–Lemeshow calibration, VIF<5, EPV≥10; two-sided p<0.05 (SPSS v26)

Figure1.ROC analysis in NP-DKD comparing uIL-6 vs UACR.  Figure2.Early (3 months) and sustained (42 months)responses in uIL-6, UACR, and eGFR.

Table 1. Baseline characteristics by DN phenotype.

Table 2. Multivariable predictors of treatment response (≥20 % UACR or ≥30 % uIL‑6 reduction).

In this cohort, baseline characteristics differed primarily by kidney injury pattern (Table 1): protein uric DKD had markedly higher UACR and lower eGFR (both p<0.001), whereas age, sex, and hypertension were comparable; uIL-6 differed modestly across groups (p=0.038). Predictors of treatment response (Table 2) showed that higher baseline uIL-6 (OR 1.18 per 10 ng/L, p<0.001) and higher systolic blood pressure (OR 1.07 per 10 mmHg, p=0.03) independently increased the odds of response, while baseline UACR and HbA1c were not informative. Discrimination analyses in NP-DKD (Figure 1) demonstrated superior performance of uIL-6 (AUROC 0.88) compared with UACR (AUROC 0.55), consistent with reports that inflammatory urinary cytokines capture risk beyond albuminuria [10–12]. Longitudinally (Figure 2), uIL-6 fell at 3 and 42 months, UACR declined more gradually, and eGFR rose slightly, supporting an early anti-inflammatory/tubulointerstitial signal preceding albumin uric change [10–12]. Creatinine/specific-gravity indexing underpins assay robustness and mitigates dilution bias [18]. 

Conclusion: The uIL-6 complements UACR in DKD evaluation. In NP-DKD, dapagliflozin lowered uIL-6 without parallel UACR change, and uIL-6 better predicted response and preservation of kidney function. Incorporating uIL-6—particularly for NP-DKD—may refine risk stratification and enable earlier assessment of therapeutic effect alongside standard CGA staging.

Recommendations: Incorporate uIL-6 into DKD assessment to identify high-risk NP-DKD patients missed by albuminuria-only strategies.Use uIL-6 as an early pharmacodynamic marker of SGLT2 treatment effect, preceding changes in UACR or eGFR.