# A higher prognostic nutritional index is inversely associated with the need for renal replacement therapy in elderly critically Ill surgical patients

## TL;DR

Higher nutritional and immune health in elderly ICU patients is linked to a lower chance of needing kidney dialysis.

## Contribution

This study shows that a higher PNI is inversely associated with the need for renal replacement therapy in elderly surgical ICU patients.

## Key findings

- A 10-unit increase in PNI reduces the odds of needing RRT by 5%.
- Patients in the highest PNI tertile had a 58% lower risk of RRT compared to the lowest tertile.
- The relationship between PNI and RRT is linear and robust to confounding factors.

## Abstract

Acute kidney injury requiring renal replacement therapy (RRT) is a critical complication in elderly surgical patients in the intensive care unit (ICU) and is associated with high mortality and healthcare costs. The prognostic nutritional index (PNI), calculated as 10 × serum albumin level (g/dL) + 0.005 × total lymphocyte count (per mm3), integrates both the serum albumin level and lymphocyte count to reflect a patient's nutritional and immunological status, however, its association with the need for RRT remains underexplored. This study aimed to evaluate the association between the PNI and need for RRT in critically ill surgical patients aged ≥ 65 years.

A secondary analysis of 3,406 elderly surgical patients in the ICU (2015–2020) from a single-center cohort was conducted. The PNI was calculated serum albumin levels and lymphocyte counts obtained at ICU admission. Patients were stratified into PNI tertiles (low: 26.50–41.00; middle: 41.50–48.50; high: 49.00–73.00). Multivariate logistic regression and subgroup analyses were applied to explore the association of the PNI with the need for RRT. Furthermore, we also examined the association between the PNI and the need for RRT by employing restricted cubic splines. The discriminative ability of the PNI was assessed using receiver operating characteristic (ROC) curves and the area under the curve (AUC).

According to the multivariate regression models, the PNI demonstrated a significant inverse association with the need for RRT after comprehensive covariate adjustment. The adjusted odds ratio (OR) for the need for RRT was 0.95 (95% CI 0.93–0.97; P < 0.0001) per 10-unit increase in the PNI. When the PNI was analyzed by tertile, patients in the middle (OR = 0.72, 95% CI: 0.54–0.97, P = 0.0285) and high tertiles (OR = 0.42, 95% CI: 0.29–0.60, P < 0.0001) presented a progressively lower risk of RRT than did those in the low tertile, with a significant dose‒response trend (P for trend < 0.0001). We further performed exploratory subgroup analyses and confirmed that higher PNI levels were independently associated with a lower risk of RRT (P for interaction > 0.05). The RCS analysis suggested a linear relationship between the PNI and the need for RRT (P for nonlinearity = 0.2848). The E-value of 2.59 demonstrates the robustness of the results against unmeasured confounding.

In geriatric surgical patients (≥ 65 years) presenting with critical illness, an elevated PNI demonstrated an inverse correlation with the need for RRT.

The online version contains supplementary material available at 10.1186/s12893-025-03240-w.