In diabetic kidney disease (DKD), inflammation, malnutrition, and lipid metabolism disorders frequently coexist and are closely interconnected. Several inflammatory biomarkers derived from routine test — such as the monocyte-to-lymphocyte ratio (MLR), monocyte-to-HDL cholesterol ratio (MHR), and prognostic nutritional index (PNI) – have been widely used and have been associated with renal function. However, previous studies have predominantly focused on prognostic value, cutoff determination, or cross-sectional correlations with disease status, whereas no research has examined the measurement stability of these biomarkers over time. This gap raises an essential methodological question: Are these inflammatory indices reliable when repeatedly measured within the same patient? This study aims to evaluate the 6-month repeatability of these biomarkers in patients with DKD using metrics such as the Intraclass Correlation Coefficient (ICC), compare the biomarkers' reliability and investigate longitudinal associations between these biomarkers and renal function.

This longitudinal study included 51 patients diagnosed with DKD each assessed at two visits separated by 6 months. Clinical characteristics and routine laboratory parameters were obtained from medical records. Inflammatory biomarkers were calculated using standard formulas. The 6-month measurement repeatability of each inflammatory biomarker was evaluated using the ICC derived from a two-way mixed-effects model with absolute agreement. Longitudinal associations were based on changes in inflammatory biomarkers and renal function over a 6-month period. This study was approved by the Ethics Committee (NO:2053/ĐHYD-HĐĐĐ; Date: August 20, 2024).

MHR and MLR had moderate reliability with ICC(3,1) = 0.62 and 0.69, respectively; while PNI showed good reliability with ICC(3,1) = 0.81 and excellent reliability when using the average of two measurements (ICC(3,2) = 0.90). After a 6-month follow-up period, changes in MLR were significantly associated with changes in both eGFR (r = –0.31, p < 0.05) and UACR (r = –0.29, p < 0.05). Similarly, changes in PNI were strongly correlated with changes in eGFR (r = 0.53, p < 0.05) and UACR (r = –0.50, p < 0.05). In contrast, changes in MHR were not significantly correlated with either ΔeGFR or ΔUACR.

PNI showed good-to-excellent reliability, indicating that it is a highly stable index when assessed longitudinally (6 months). In contrast, MHR and MLR show moderate reliability, reflecting greater within-person biological variability. Over the 6-month follow-up period, changes in MLR – and particularly PNI – showed significant associations with changes in renal function, whereas MHR did not demonstrate meaningful relevance within this time frame.