In recent years, with the increasing prevalence of AP year by year [8, 9, 10], the early, rapid and effective screening of SAP high-risk patients poses a great challenge to clinical treatment. In clinical practice, the classification and prognosis of AP are mainly evaluated based on the scoring system. Therefore, it is of great significance to establish a simple prediction tool for clinical practice.
Our analysis of the collected AP cases showed that six indicators could predict the probability of SAP, and men are more likely to develop SAP. In previous studies, the association between gender and SAP was not clear. However, previous studies demonstrated that acute biliary pancreatitis was significantly more common in female than in male patients, in contrast, alcoholic AP is more likely to occur in male patients [11, 12]. To our knowledge, through different channels, alcohol can directly damage the pancreas, and even lead to pancreatic secretion dysfunction by different mechanisms [15]. Although patients who have never consumed alcohol can develop pancreatitis, alcohol appears to increase the sensitivity of the pancreas to other etiologic factors, and the risk of pancreatitis undoubtedly increases with alcohol consumption. Previous studies have shown that alcohol use is the single most common cause of chronic pancreatitis (its attributable risk is about 40%), and after gallstones, is the second-most common cause of AP [13, 14, 15]. This can explain why male patients are more likely to develop SAP than female patients.
Previous studies have shown that gallstone and alcohol are the most common etiological factors in China, and gallstone ranks first among the known etiological factors [1, 10, 11]. Consistently, in our study, gallstone was also the main etiological factor of AP, responsible for 61.8% of all factors (Table 1). However, hyperlipidemia was also one of the significant etiological factors for AP in our study, and the incidence of SAP caused by hyperlipidemia was significantly higher than that caused by gallstone. Zhu et al. [11] analyzed 3260 hospitalized patients between 2005 and2012 from AP database and found that there was a significantly higher incidence of SAP in the hyperlipidemia group than cholelithiasis (18.2% vs 14.0%, P = 0.022) and hyperlipidemia-induced pancreatitis leads to poor prognosis. Similarly, in our study, hyperlipidemia-induced pancreatitis in the SAP group accounted for an important part and one of the major causes of AP.
In our study, it can be found that the probability of SAP in patients with hypertension was higher than that in patients without hypertension. Hypertension is often accompanied by hypercholesterolemia, and hypercholesterolemia and hypertension have synergistic pro-oxidant, pro-inflammatory, and prothrombotic effects [16, 17, 18]. Therefore, hypertension, with or without hyperlipidemia, increases the risk of AP, aggravates the inflammatory process of AP, and even leads to the development of SAP.
It can be seen from the data that calcium ions had significant differences between the non-SAP group and the SAP group in this study. Serum calcium in the non-SAP group was significantly higher than that in the SAP group. Another study found that the serum calcium level in non-SAP patients is higher than that on admission, showing that serum calcium ion may be a potential independent predictor of AP severity [19, 20]. Obviously, the Ca2+ level accounts for a large proportion in our model nomogram, and the lower Ca2+ level indicates a higher risk of SAP.
To our best knowledge, there are few studies on the association between AP and albumin, and their correlation is still unclear. Hypoalbuminemia is associated with inflammation, and low serum albumin levels caused by inflammation-induced capillary leakage or disease-related anorexia are associated with poor outcomes [22, 23]. Moreover, low serum albumin was proved to be predictive tool for inpatient mortality [21, 22, 23]. Through multivariate logistic regression, it was demonstrated that serum albumin could be used as an independent predictor of SAP. Nevertheless, previous studies have shown that albumin not only has good diagnostic accuracy for SAP, but also has high predictive ability for in-hospital mortality in patients with AP [24, 25, 26]. It can be seen from the individual analysis that AP patients were more likely to develop SAP and poor prognosis with the decrease of serum albumin level. In summary, albumin can be a potential predictor of SAP.
In this study, we developed and validated a machine learning-based model that incorporates the clinical features and etiologies in patients with AP. The nomogram demonstrated favorable discrimination in both training cohort (AUC, 0.782) and validation cohort (AUC, 0.764) and good calibration, which confirms that the training-validation model achieved excellent predictive efficacy. DCA indicated the clinical usefulness of the prediction model. By establishing the nomogram prediction model, a simple prediction tool is provided. The probability of SAP in AP can be routinely estimated in clinical practice within 24 hours of admission through a series of convenient and accessible laboratory tests. The above indicators are easy-to-obtain indicators, and the possibility of SAP can be obtained within 1 minute by using this nomogram (Fig. 2). From this perspective, clinicians can flexibly carry out early fluid resuscitation and close monitoring according to the early predictive value of AP patients, and even quickly transfer patients to hospitals with better pancreatic care or large medical institutions.
In this study, individual nomogram performed well in both training and the validation cohorts, and it also showed good calibration in both training and validation cohorts. However, there are some limitations to our analysis. The main limitation of this study may be that it is not a prospective but a single-center retrospective study and the selection bias cannot be ignored. Secondly, the sample size of this study is still limited, so an external validation cohort is necessary for our study verify the model nomogram. Finally, although the nomogram showed good performance in calibration and clinical usefulness, AUCs in the training (AUC = 0.782) and validation (AUC = 0.764) cohorts were unsatisfactory. In the next step, we will focus on multi-center validation and select more accurate features to develop a deep learning model to obtain high-level evidence with clinical application.