In the present study, we retrospectively analyzed data from 413 cirrhosis patients and found that 58 (11.4%) patients with SBP experienced complications, a prevalence consistent with previous reports [3, 4]. We found that all SBP patients were uncompensated, suggesting that cirrhotic status was significantly associated with SBP. We also found that cirrhotic patients with cancer are more prone to SBP compared to non-cancer patients. The results of the laboratory test indices showed that most of the inflammatory indices, liver function indices and nutritional indices were significantly different between patients with and without SBP; In addition, we observed that laboratory test indices in uncompensated patients with cirrhosis were similar to those in patients with complete cirrhosis. Importantly, we found that cancer had differential effects on some laboratory test indices in cirrhotic patients without SBP, but had little effect in patients with SBP. Next, we examined the laboratory test indices associated with SBP in uncompensated cirrhotic patients using two machine learning methods and validated by a logistic regression model. The results showed that ALB, NLR and FNR were independently associated with the SBP in which FNR had not previously been reported. Finally, we identified neutrophils, ALP, and CAR, all of which were associated with survival in cirrhotic patients with or without SBP, and the prognostic value constructed by these three indices was high compared to other indices. Taken together, these results showed that several indices were associated with the occurrence of SBP in uncompensated cirrhotic patients and FNR was a new biomarker for the diagnosis of cirrhosis with SBP. We also identified three indices that are significantly associated with the prognosis of uncompensated cirrhotic patients.
SBP is a common complication in uncompensated cirrhotic patients. Currently, the diagnosis of SBP in cirrhotic patients relies on testing for ascites, and abdominal paracentesis is an invasive surgery that increases the risk of infection [16]. Therefore, it is helpful for cirrhotic patients to find a non-invasive approach to diagnosing SBP. Using laboratory test indices from blood samples to diagnose SBP or predict survival in cirrhotic patients is a viable approach in clinical practice. Previous studies have identified several common blood indices related to the SBP in cirrhosis, including CRP and NLR [11]. In the present study, we confirmed the diagnostic value of NLR in SBP of cirrhosis, indicating the robustness of this index. More importantly, as the diagnostic value of FNR in SBP in cirrhosis was reported for the first time, these results underscore the role of FNR in uncompensated patients with cirrhosis.
Serum ferritin reflects the body's iron stores and was increased in iron overload and decreased in patients with iron deficiency disorders. Elevated liver iron would promote increased ferritin synthesis [17], and ferritin activates production of collagen and liver fibrogenesis[18]. Therefore, serum ferritin could be a useful marker of ongoing fibrosis[19]. In this study, we found that serum ferritin levels were significantly different between cirrhotic patients with and without SBP, but as shown in Table 3, the change in ferritin levels was strongly influenced by the cancer, suggesting that the change in ferritin in cirrhotic patients with SBP were affected by cancer, so it could not be an independent index to diagnose SBP in cirrhosis. We therefore used a combination of ferritin with other blood indices. One study reported that FAR was able to determine mortality in critically ill COVID-19 patients treated in the ICU [20]. Our study showed that FAR was elevated in uncompensated cirrhotic patients and patients with SBP, but was not an independent index of SBP and was not associated with cirrhotic patient survival.
FNR was calculated from the ratio of ferritin and neutrophils. Neutrophil count is a sensitive index that reflects inflammation in the body. The combination of neutrophils with other indices has proven critical in diagnosing or predicting multiple diseases such as platelets to neutrophils ratio in a stroke [21], eosinophil-neutrophil ratio in tumors [22], platelet-to-neutrophil ratio in lupus nephritis [23]. This evidence showed that the combination of neutrophils with other indices had a more important value than the individual index. This study found that FNR was independently associated with risk of SBP and with worsening in patients with cirrhosis. We speculated that the mechanism underlying the value of FNR in cirrhotic patients with SBP might be that ferritin reflects the status of cirrhosis while neutrophils reflect infection of the peritoneum, and this combination might reflect the overall status of cirrhotic patients with SBP reflect better.
Regarding the prognostic value of laboratory test indices associated with cirrhotic patients, one study reported that serum CRP levels were associated with a higher mortality rate in patients with SBP[24], ascitic fluid lactate and NLR[25], and calprotectin[26] were associated with the mortality of patients with SBP. The present study showed that blood neutrophils, ALP and CAR levels were significantly associated with the prognosis of uncompensated cirrhotic patients regardless of the total number of patients or patients with SBP, and the prognostic value of the model constructed by these indices was better than the individual Index. These results indicate that the combination of certain laboratory tests indices could achieve a better prognostic value in cirrhotic patients.
There were several limitations in this study. First, although we included a large sample of cirrhotic patients, the number of SBP was relatively small, the survival analysis for cirrhotic patients with SBP could be performed. Second, since this study is retrospective, the chosen bias is inevitable and confounding factors could undermine the robustness of the results. Third, this study is a single center research, so our results should be interpreted with caution when extrapolating to other population regions. Therefore, a prospective multi-center design cohort is warranted to validate our results.