Comprehensive Assessment of Inflammatory Indices to Predict Outcomes in Acute Pancreatitis

To the Editor,

We read the recent publication by Biyik et al. with keen interest [1]. The authors report the role of two novel inflammatory markers, the systemic immune-inflammation (SII) index and the systemic inflammation response index (SIRI), in predicting outcomes in patients with acute pancreatitis. These findings have clinical implications, as using simple inflammatory indices to independently predict acute kidney injury (AKI) and severe acute pancreatitis (SAP) is particularly valuable in low-resource settings. Previous studies have recorded the importance of the SII and the SIRI in various inflammation-driven outcomes in critically ill patients [2–4]. However, very few studies simultaneously report both the SII and SIRI and provide meaningful comparisons of their respective prognostic performances. The authors have identified a significant lacuna in the literature and have reported receiver operator characteristic (ROC) analyses for both the SIRI and SII, demonstrating the superiority of the SII through this analysis.

The SII incorporates the neutrophil, lymphocyte, and platelet count, whereas the SIRI incorporates the neutrophil, monocyte, and lymphocyte count. In an attempt to combine all four cell lines into one comprehensive inflammatory index, the pan-immune inflammation value (PIV) has recently been demonstrated to have prognostic value in malignancies [5, 6]. This new inflammatory index includes components of both the SII and the SIRI, so it may theoretically outperform both. Including the PIV in the present study and comparing its performance with the SII or SIRI would have been a valuable addition by the authors.

Secondly, it is worth noting that both the SII and SIRI provide equal weightage to all their component cell counts. For instance, the SII assumes a direct linear association with the neutrophil and platelet count and an inverse relationship with lymphocyte count. While the SII is valuable due to its simplicity in the calculation, the individual contribution of one component of the SII may be greater than or less than the other. A similar phenomenon may hold for the SIRI. Future studies modeling the precise relationships of individual cell counts with outcomes are needed to robustly determine the weights of the different components of these inflammatory indices. Access to simple hemogram parameters such as neutrophil, monocyte, lymphocyte, and platelet counts is relatively easy and inexpensive in almost all clinical settings. However, using more sophisticated statistical modeling will allow clinicians to extract maximum utility and efficiency from the parameters.

At different points in the clinical course, the degree of variability observed in different cell counts may not be comparable. For example, with the progression of SAP, worsening thrombocytopenia may result in a reduction in the SII. Parallelly, with an increase in systemic inflammation, there may be a rise in neutrophil count, a fall in lymphocyte count, and a consequent rise in the SII. This leads to a paradoxical rise and fall in the SII simultaneously due to the conflicting directional changes in the component cell counts. Previous studies have reported the importance of recording the kinetics, or dynamic changes during the clinical course, of various inflammatory cell counts [7, 8]. An analysis of the dynamic changes in the SII and SIRI, resulting from clinical improvement or worsening, duration of hospital stays, type of therapy received, and any comorbid conditions will be important areas of future research.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

No original datasets were utilized in the present manuscript.