# Correlation between serum prolactin and the systemic immune-inflammation index in diabetic kidney disease: a cross-sectional study

## TL;DR

This study finds a nonlinear link between serum prolactin and immune-inflammation in diabetic kidney disease patients, suggesting a potential role in disease progression.

## Contribution

The study reveals a novel nonlinear association between serum prolactin and the systemic immune-inflammation index in diabetic kidney disease.

## Key findings

- Serum prolactin levels above 282.85 mIU/L show a positive association with the systemic immune-inflammation index (SII).
- A 100 mIU/L increase in serum prolactin corresponds to a 7.10 unit increase in SII after multivariable adjustment.
- The relationship between serum prolactin and SII is nonlinear, with a threshold effect observed at 282.85 mIU/L.

## Abstract

Prolactin (PRL) is increasingly recognized as a pleiotropic hormone with potent immunoregulatory properties; however, its involvement in systemic inflammation among diabetic kidney disease (DKD) patients has not been defined. This study aimed to investigate the potential association between serum PRL levels and micro-inflammation in patients with DKD.

In this cross-sectional investigation, 994 patients with type 2 diabetes mellitus (T2DM)-associated DKD were enrolled. Multivariable linear mixed-effects models were used to quantify the relationship between serum PRL and the systemic immune-inflammation index (SII) and other clinical parameters. Restricted cubic spline (RCS) analyses were fitted to test for non-linearity and stratified and sensitivity analyses were performed to assess robustness.

The median serum PRL level was 344.40 mIU/L (interquartile range: 258.80–463.10). After multivariable adjustment, serum PRL were positively associated with white blood cell count, neutrophil count, serum ferritin, serum phosphorus and intact parathyroid hormone (iPTH) levels, and inversely associated with serum albumin. For every 100 mIU/L increase in serum PRL, the SII increased by an average of 7.10 units (95% CI: 3.13 to 11.07; p = 5.12 × 10-4). Stratified and sensitivity analyses confirmed the robustness of this association. RCS analysis revealed a significant nonlinear relationship between serum PRL and SII (p for nonlinearity = 0.002), with an inflection point at 282.85 mIU/L. PRL levels above this inflection point showed a significant positive association with SII, whereas levels below it showed a negative association.

In patients with DKD, serum PRL exhibits an independent, nonlinear association with SII, characterized by a threshold around 282.85 mIU/L. This finding suggests that PRL may be linked to the dysregulated immune-inflammation axis in DKD, warranting further mechanistic and longitudinal investigation.