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Albumin/fibrinogen ratio (AFR): a significant predictor of postoperative delirium in older patients undergoing non-neurosurgical and non-cardiac surgery

BMC Geriatrics volume 25, Article number: 142 (2025) Cite this article

Abstract

Objective

The purpose of this research was to evaluate the prognostic significance of preoperative albumin to fibrinogen (AFR) for postoperative delirium (POD) in older patients with non-neurosurgical and non-cardiac surgery.

Method

The retrospective cohort study included a group of patients aged 65 and above who underwent non-neurosurgical and non-cardiac surgery at the First Medical Center of Chinese PLA General Hospital from January 2014 to December 2021. AFR and POD correlation was evaluated through univariate and multivariable logistic regression analysis, as well as propensity score matching (PSM) and subgroup analysis.

Results

In our study, the occurrence of POD was 2.9% (1566/53,609), with the AFR threshold identified as 10.625 based on the ROC curve. The study identified AFR ≤ 10.625 as a significant predictor of POD in both univariate and multivariable regression analyses, and the odds ratios (OR) were 2.65 (2.40–2.93), 1.98 (1.79–2.21), 1.51 (1.34–1.70), 1.27 (1.13–1.43) and 1.32 (1.14–1.53) in four models and the PSM model.

Conclusion

AFR is a valuable predictor for predicting the development of POD in older patients receiving non-neurosurgical and non-cardiac procedures. This finding highlights the importance of preoperative assessment of AFR in these patients to better predict and manage the risk of POD.

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Introduction

Postoperative delirium (POD) is a challenging clinical syndrome that occurs primarily in older patients after surgery [1]. Until today, there is still no effective pharmacological treatment for delirium [2]. The current mainstream approach remains non-pharmacological interventions. It is characterized by acute episodes of fluctuating cognitive impairment, attention disorders, and confusion [3, 4]. The prevalence of POD varies widely, with reports ranging from 2.5 to 70% for different types of surgery [5]. Delirium is influenced by various factors, including advanced age, cognitive deficits, and chronic illnesses such as heart failure, cancer, and cerebrovascular disease. Other contributing factors are depression or anxiety, inflammation, a history of stroke, poor nutritional status, fluid and electrolyte balance disorders, and dependence on drugs or alcohol [6, 7]. The adverse effects of POD include longer hospital stays, increased health care costs, long-term cognitive decline, and higher mortality rates [8, 9]. In addition, POD often complicates the postoperative process in older patients, resulting in an overall reduction in quality of life and greater reliance on medical services.

The ratio of albumin to fibrinogen (AFR), is emerging as a novel prognostic immune biomarker. Albumin, a major plasma protein, is synthesized and secreted by the liver. It usually makes up more than 50% of the protein in the blood, and its concentration reflects nutritional status and systemic inflammation [10]. While fibrinogen, a glycoprotein synthesized by liver epithelial cells, plays a key role in regulating blood clotting. At the same time, when the body has inflammatory stimulation, its synthesis is greatly enhanced [11]. Alterations in the AFR could reflect a state of malnutrition, or an inflammatory response, all of which are also risk factors for the development of POD [12]. In the elderly, who are often subject to nutritional deficits and chronic inflammatory states, preoperative assessment of AFR may provide valuable insights into the risk of developing POD [13, 14]. Previous studies have shown the significance of AFR in predicting patient outcomes, particularly in various cancers such as non-small cell lung cancer (NSCLC), rectal cancer, gastric cancer, chronic lymphocytic leukemia, and breast cancer [15,16,17]. Moreover, AFR has also been identified as an independent predictor of POD after total joint arthroplasty [18]. However, existing studies are limited to specialty surgery, and few studies have revealed the relationship between AFR and POD in older patients with multiple surgical modalities.

In this study, we explored the potential of AFR as a predictive marker of POD in older patients. By establishing a large cohort that included 53,609 patients, our study aimed to assess the effectiveness of AFR in predicting POD risk in patients aged 65 and over undergoing surgery other than cardiac or neurosurgery.

Materials and methods

Patients

The study is a retrospective, observational cohort study. It was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the First Medical Center of the Chinese People’s Liberation Army General Hospital (No. S2019-311-03). Informed consent was not required because the study was retrospective. To protect patient privacy, personally identifiable information was not extracted and only anonymous records were used.

Non-neurosurgical and non-cardiac procedures performed under anesthesia from January 2014 to December 2021 were considered eligible for inclusion. Exclusion criteria: (1) Endoscopy; (2) Emergency surgery; (3) American Society of Anesthesiologists (ASA) V; (4) Lack of exposure factor AFR.

Data collection

Baseline characteristics and demographic information of the patients were collected from hospital records. Additionally, perioperative data related to postoperative delirium was specifically gathered to facilitate a more comprehensive and precise analysis. The data collected included:

Demographic data: age, sex, body mass index (BMI), smoking, and drinking history.

Clinical data: ASA status, preoperative comorbidities including diabetes, hypertension, cardiovascular and cerebrovascular diseases, chronic obstructive pulmonary disease (COPD), anxiety, and depression, chronic kidney disease (CKD).

Preoperative medication: benzodiazepines, opioids, anticholinergic drugs, antipsychotic, and nonsteroidal anti-inflammatory drugs (NSAIDs).

Laboratory tests: white blood cell (WBC), hemoglobin (Hb), platelets, glucose (Glu), thrombin time (TT), prothrombin time (PT), creatinine (Cre), fibrinogen, albumin, aspartate aminotransferase (AST), and alanine aminotransferase (ALT).

Details related to surgery and treatment included surgical procedure type, anesthesia method, duration of surgery and anesthesia. Additional information gathered comprised urine output, blood loss, colloid and crystalloid volumes, blood transfusion, and intraoperative medications (such as anticholinergics, benzodiazepines, antipsychotics, opioids, and NSAIDs). Data also covered the duration of systolic blood pressure (SBP) above 140 mmHg, mean arterial pressure (MAP) below 60 mmHg, and diastolic blood pressure (DBP) above 90 mmHg.

Outcomes measurement

Patients were diagnosed with postoperative delirium using the Chart-based Delirium Identification Instrument (CHART-DEL) within a week of their surgery. The CHART-DEL is a validated method that can be used to review charts (medical records) to detect the presence of delirium [19]. Patients were excluded from the study if their preoperative medical records showed the diagnosis of delirium. Trained neurologists reviewed the medical records of patients who met the criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) to make the final diagnosis [20].

Correlation between AFR and POD

The optimal threshold for AFR in predicting POD was determined to be 10.625 using the receiver operating characteristic (ROC) curve. Following this, AFR was divided into two categories using the specified threshold. Furthermore, AFR was segmented into four categories according to quartiles. Then we used logistic regression to explore the relationship between AFR and POD, treating AFR as a continuous, binary, and four-category variable.

Initially, unadjusted univariate logistic regression analysis was conducted. Based on these considerations, model 1 was constructed by adjusting for sex, age, BMI, and ASA status. Model 2 included additional variables such as smoking and alcohol use, diabetes, hypertension, cardiovascular disease, cerebrovascular disease, CKD, depression, preoperative drugs including anticholinergics, benzodiazepines, antipsychotics, opioids, and NSAIDs, WBC, Hb, platelet, Glu, TT, PT, Cre, AST. To enhance the analysis further, model 3 incorporated intraoperative data, encompassing the type and the length of surgery and anesthesia, urine output, blood loss, colloid and crystalloid volumes, blood transfusion, the use of NSAIDs, benzodiazepines, and dexmedetomidine, duration of MAP < 60 mmHg and SBP > 140 mmHg, while retaining the variables from previous models.

Propensity score-matching analysis

To reduce the potential impact of confounding factors, we utilized propensity score (PS) analysis and PSM to investigate the relationship between AFR and POD. In this study, we employed one-to-one matching using a greedy algorithm, setting a maximum caliper of 0.1, to pair patients with POD to those without POD who had similar PS. Patients without a suitable match within this range were excluded from the analysis. To ensure the comparability of matched patients, we used kernel density plots to compare the distribution of propensity scores before and after matching. We also calculated the standardized mean difference (SMD) for each baseline variable between the two groups, with a value of < 0.1 considered negligible.

Subgroup analyses

To investigate potential sources of confounding factors in the influence of AFR on POD among different subgroups, our analysis was stratified based on age, sex, ASA status, hemoglobin level, surgical duration, and duration of MAP < 60 mmHg. The outcomes of our subgroup analyses are depicted through forest plots, which succinctly illustrate the predictive impact of AFR on POD within each subgroup.

Statistical analysis

In this study, continuous variables were presented as mean ± SD for normally distributed data, and as median with IQR for non-normally distributed data. Continuous variables were analyzed using the t test or Mann-Whitney U test. Categorical variables were reported as counts (percentages) and analyzed using either Fisher’s exact test or the χ2 test. A two-tailed P-value of 0.05 was established as the threshold for statistical significance. All analyses were performed using R software version 4.1.3.

Results

Patient characteristics

We conducted a retrospective cohort of 57,597 patients aged over 65 who received non-neurosurgical and non-cardiac surgery between January 2014 and December 2021. After applying the above exclusion criteria, a final cohort of 53,609 patients was analyzed (Fig. 1). The cohort had a median age of 70 years (IQR: 67–74 years), with 48.2% of the participants being female. The incidence of POD was 2.9%.

Fig. 1
figure 1

Diagram of the enrollment process for the study

Full size image

By using the ROC curve, we determined the best threshold for preoperative AFR to predict POD in older patients as 10.625, with an AUC of 0.65 (0.63–0.66), shown in Additional file Fig. A1. We then divided patients into two groups based on this threshold: AFR ≤ 10.625 (n = 16,797) and AFR > 10.625 (n = 36,812).

There were statistically significant differences (P < 0.05) between the two groups in baseline characteristics, perioperative data, except for hypertension, anxiety, depression, preoperative use of NSAIDs, and duration of DBP > 90 mmHg. Compared with the other group, the group of AFR ≤ 10.625 had more women, older individuals, lower BMI, higher prevalence of smoking history, and a larger proportion of non-drinkers. This group also showed a higher incidence of comorbidities, including diabetes, cardiovascular and cerebrovascular diseases, CKD, and COPD. Additionally, the duration of anesthesia and surgery was longer in this group (Table 1).

Table 1 Baseline patient characteristics between the groups
Full size table

Correlation between the AFR and POD

We employed four models to investigate the association between AFR and POD. In the analysis of AFR as a continuous variable, univariate logistic regression showed a significant correlation, with an OR of 0.86 (95% CI: 0.85–0.87, P < 0.001). Lower AFR was found to be linked to a higher risk of POD in the multivariate logistic regression models, with adjusted odds ratios of 0.90, 0.94, and 0.97, respectively (P < 0.001, Additional file Table A1).

Furthermore, we identified the optimal threshold value for AFR to be 10.625 and classified the cases into two groups based on this criterion. In the univariate analysis, the OR for the group with AFR ≤ 10.625 was 2.65 (95% CI: 2.40–2.93, P < 0.001). The correlation was consistently strong in all multivariable logistic regression models, with ORs ranging from 1.13 to 2.21 (P < 0.001, Table 2).

Table 2 Association between AFR and POD with logistic regression models and PSM analysis
Full size table

Then we categorized patients into four groups based on quartiles of AFR: AFR ≤ 9.95, 9.95 < AFR ≤ 12.27, 12.27 < AFR ≤ 14.50, and AFR > 14.50. Our univariate analysis showed that patients in the AFR ≤ 9.95 and 9.95 < AFR ≤ 12.27 groups had a significantly higher risk of developing POD compared to those in the AFR > 14.50 group (P < 0.001). This trend persisted even after conducting multivariate regression analysis, confirming that lower AFR is a consistent predictor of increased POD risk. After adjusting for various variables, the AFR ≤ 9.95 group still had a significantly higher risk of POD compared to the AFR > 14.50 group (OR = 1.27, P < 0.01) in Model 3 (Additional file Table A2).

In addition, the decision curve analysis (DCA) conducted for AFR demonstrated that considering AFR could lead to favorable net benefits for patients (Fig. 2A). Additionally, the calibration curve displayed reliable performance (Fig. 2B).

Fig. 2
figure 2

(A) The Decision Curve Analysis of AFR for POD. (B) The Calibration curve of AFR for POD. Abbreviations: simple model = unjusted model; complex model = model 3

Full size image

Analysis and adjustment using propensity score matching

To control for potential confounding variables, we employed PSM in our cohort study, with a 1:1 ratio between the AFR > 10.625 group and the AFR ≤ 10.625 group. We successfully matched 12,200 patients in each group by considering 28 variables, including sex, age, BMI, smoking history, CKD, preoperative use of opioid and psychotropic drugs, Hb, WBC, platelet count, Glu, TT, PT, AST, type and length of surgery and anesthesia, ASA status, urine output, blood loss, colloid and crystalloid volumes, blood transfusion, the use of NSAIDs and benzodiazepines, duration of SBP > 140 mmHg and the duration MAP < 60 mmHg. The propensity score distribution both before and after performing PSM was illustrated in Fig. 3A and B.

Fig. 3
figure 3

Distribution of propensity scores in patients with AFR > 10.625 and AFR ≤ 10.625. (A) Before matching. (B) PSM matching. Abbreviations: AFR Alb/Fib ratio

Full size image

After matching, the baseline characteristics between the two groups were well-balanced, with all covariates exhibiting SMD < 0.1. Following PSM, AFR continued to independently predict POD in the multivariable logistic regression analysis. The OR for AFR ≤ 10.625 was 1.32 (95% CI: 1.14–1.53, P < 0.001), as shown in Table 2. Additional multivariable logistic regression analysis outcomes can be found in Table A3.

Subgroup analyses

Subgroup analysis revealed that AFR ≤ 10.625 was statistically significant across subgroups defined by gender, age, ASA status, Hb, and duration of surgery (P < 0.05), as shown in Fig. 4. Based on the OR values in each subgroup, it was found that AFR had a stronger association with POD in specific patient subgroup, which included female patients, aged ≤ 70 years, with ASA status ≥ III, duration of surgery ≤ 120 min, Hb > 130 g/L, and duration of MAP ≤ 60 mmHg for ≤ 10 min.

Fig. 4
figure 4

Subgroup analyses of the association between AFR and postoperative delirium. Abbreviations: AFR Alb/Fib ratio; POD, postoperative delirium; OR, odds ratio; CI, Confidence interval; ASA, American Society of Anesthesiologists classification; Hb, hemoglobin; MAP, mean arterial pressure

Full size image

Discussion

This study aimed to investigate the predictive effect of AFR on POD in older patients. Previous studies have identified low postoperative AFR as a risk factor for POD in older patients, but were limited by small sample sizes and narrow focus on specific surgeries. To address these limitations, we conducted a large retrospective cohort study with 53,609 patients undergoing various procedures. Rigorous statistical methods, including univariate and multivariate logistic regression, PSM, DCA, and calibration curves, were employed. Our results showed that preoperative AFR remained a reliable predictor of POD across different surgical procedures.

Our study provides strong evidence supporting AFR as a significant predictor of postoperative delirium (POD) in surgical patients. Lower AFR values were associated with a higher incidence of POD (P < 0.001) when considering AFR as a continuous variable. Using a binary variable with a cutoff of 10.625, AFR ≤ 10.625 was identified as a risk factor for POD in both univariate and multivariable logistic regression analyses (P < 0.001). Further analysis, dividing AFR into four groups, confirmed the association between AFR ≤ 9.95 and increased odds of POD. After adjusting for 28 variables and performing 1:1 propensity score matching, with each group consisting of 12,200 patients, the influence of other variables was eliminated (SMD < 0.1). Multivariable logistic regression analysis of the PSM matched cohort revealed that a decrease in AFR remained a predictive factor for POD (P < 0.001). These findings were consistent across different subgroups, including various age groups, ASA status, genders, hemoglobin, and surgical durations. Patients with AFR ≤ 10.625 had an increased risk of developing POD in the subgroup with a duration of MAP < 60 mmHg ≤ 10 min.

Albumin, an abundant plasma protein in the human body, is considered a marker of weakness, nutrition, inflammation, and functional capacity [21, 22]. Several cross-sectional studies have suggested a positive correlation between serum albumin levels and MMSE scores in hip fracture and AD patients [23, 24] Previous research has indicated that abnormal albumin is a risk factor for POD in cardiac surgery patients, and low albumin levels are also associated with delirium prediction in non-cardiac surgery [25, 26]. In our previous study, we also found that the albumin-related Prognostic Nutritional Index (PNI) can be used to predict postoperative delirium [27]. The reason for this association may be that low albumin suggests malnutrition, inflammation, and lower levels of function in the elderly, all of which are known risk factors for POD. Additionally, a study by Jee et al. found a negative correlation between serum albumin and amyloid-beta (Aβ) deposition, suggesting that albumin may play a role in regulating Aβ levels [24, 28]. Recent research has also shown a correlation between Aβ deposition and the severity of perioperative delirium [29, 30]. Fibrinogen is a multifunctional protein that circulates in the blood as a soluble dimer [31]. Recent studies have found that fibrinogen has multiple effects on central nervous system inflammation activation, induction of brain hemorrhage formation, promotion of cognitive decline, and inhibition of repair [32]. The mechanism involves leakage of fibrinogen into the brain when the blood-brain barrier is disrupted, leading to glial cell activation, axonal injury, inhibition of oligodendrocyte progenitor cell (OPC) differentiation and myelin regeneration, binding to Aβ, opening the blood-brain barrier by direct interaction with brain endothelial cells, inducing astrocytic scar formation, and inhibiting neural dendrite growth [33, 34]. Previous research evaluating the proteome of cerebrospinal fluid in patients with delirium identified 16 abnormal proteins, including fibrinogen, providing evidence for the relationship between fibrinogen and delirium [35]. AFR, as the ratio of these two biomarkers, is currently widely used for predicting the prognosis of tumors and has predictive value in acute pancreatitis and rheumatoid arthritis [27, 36, 37]. Additionally, Gao et al. found that Fibrinogen/Albumin Ratio (FAR) is an effective indicator for predicting the prognosis of triple negative breast cancer (TNBC), and its mechanism may be related to chronic inflammation promoting tumor progression, while malnutrition aggravates cancer cachexia [38]. Kim KS et al. demonstrated that FAR is a feasible and useful marker for predicting one-year mortality in critically ill patients in the intensive care unit, and its potential factors are still related to inflammation, immunity, and nutritional status [39, 40]. This further confirmed the association between AFR and inflammation and nutritional status, explaining the predictive effect of AFR on POD.

Our study has some limitations that deserve consideration. Firstly, the retrospective nature of the study may have contributed to a relatively low incidence of POD, despite the inclusion of many patients. This may be due to low activity-delirium being difficult to diagnose [41]. Secondly, our study only focused on preoperative experiments and examined the predictive value of preoperative AFR for POD. The changes in AFR before and after surgery may have a better predictive value for POD. Moreover, it remains unclear whether targeted interventions for patients with low preoperative AFR can effectively reduce the occurrence of POD, which requires further exploration in future studies.

Conclusion

To summarize, the preoperative AFR demonstrates predictive value for POD in non-neurosurgical and non-cardiac patients. AFR serves as an easily obtainable indicator. Considering AFR in preoperative evaluations can be a valuable risk stratification strategy for POD, potentially leading to a reduction in its incidence among these patient populations.

Data availability

All the data shown in this study is available from the corresponding author upon request.

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Acknowledgements

We would like to thank Tong-Yan Sun and Wei Wei of Hangzhou Le9 Healthcare Technology Co., Ltd., for help in the clinical data collection of this study.

Funding

This work was supported by the National Key Research and Development Program of China [No.2018YFC2001901, No.2024YFA1012102].

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Author notes

  1. Jiang Huo and Yuxiang Song contributed equally to this work.

Authors and Affiliations

  1. Department of Anaesthesiology, The First Medical Center of Chinese PLA General Hospital, Beijing, 100853, China

    Huo Jiang, Yuxiang Song, Weidong Mi & Yanhong Liu

  2. Department of Anaesthesiology, The Fifth Medical Center of Chinese PLA General Hospital, Beijing, 100071, China

    Huo Jiang, Jing Lu, Guijin Dou, Huixian Chen & Yingqun Yu

  3. National Clinical Research Center for Geriatric Diseases, Chinese PLA General Hospital, Beijing, 100853, China

    Weidong Mi & Yanhong Liu

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  1. Huo Jiang
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Contributions

J.H, Y.X.S and Y.H.L conceptualized and designed the study. W.D.M obtained funding. Y.X.S, J.L and G.J.D collected the data. J.H, Y.Q.Y and H.X.C analysed data, prepared and reviewed figures. Y.X.S contributed for statistical analysis. J.H drafted the manuscript. Y.H.L and W.D.M critically revised the manuscript. All authors gave the approval of final version of paper.

Corresponding authors

Correspondence to Weidong Mi, Yingqun Yu or Yanhong Liu.

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Huo, J., Song, Y., Lu, J. et al. Albumin/fibrinogen ratio (AFR): a significant predictor of postoperative delirium in older patients undergoing non-neurosurgical and non-cardiac surgery. BMC Geriatr 25, 142 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12877-025-05714-1

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BMC Geriatrics

ISSN: 1471-2318

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