This study is a single-center, retrospective, and case-controlled study.

We retrospectively reviewed the records of a total of 166 patients with STB who underwent lesion debridement in our hospital from January 2012 to May 2020 to form the derivation set.

The included patients aged between 14 and 70 had thoracic or lumbar tuberculosis for the first time, and their involved lesions are less than 3 segments. Recorded and analyzed the clinical characteristics including age, gender, height, weight, body mass index (BMI), comorbidities (diabetes, pulmonary tuberculosis), smoking history, drinking history, operation time, operation blood loss, preoperative hemoglobin, preoperative lymphocytes, preoperative albumin, preoperative C-reactive protein (CRP), preoperative erythrocyte sedimentation rate (ESR), and course of the disease.

From June 2020 to January 2022, we prospectively included 102 patients with STB who underwent lesion debridement in our hospital to form the validation set. The inclusion criteria and exclusion criteria of the validation set are consistent with the derivation set.

Measurement data were listed as the mean ± standard deviation (SD) or median (minimum, maximum). Mann-Whitney rank-sum tests or t-tests were used to compare the measurement data between the groups. IBM SPSS (version 25.0 for Windows; SPSS, Chicago, IL, United States) was used for logistic regressions to analyze the univariate and multivariate factors for postoperative hypoalbuminemia. Univariate logistic regression analysis was conducted on clinical characteristics to obtain predict factors and then multivariate logistic regression analysis was conducted on these significant factors to confirm the final significant factors. Thresholds for continuous variables (preoperative albumin and operation time) were analyzed using ROC curves. The items of the scoring scale are determined by multivariate logistic regressions, and the weighted score of each item was based on the relative size of the OR value according to the method reported by Kharbanda et al. (18). The ROC curve analysis was used to find the diagnostic threshold of the scale of which the sensitivity and specificity were obtained to access the diagnostic accuracy.

This study was in accordance with the Declaration of Helsinki (as revised in 2013) and was approved by the Institutional Ethics Board of The First Affiliated Hospital of Chongqing Medical University (No. ChiCTR1800019109).

Among the total of 166 patients, 131 patients had postoperative hypoalbuminemia and 35 patients did not suffer (Table 1). Seventy-six males and 55 females suffered from postoperative hypoalbuminemia, and 22 male and 13 female did not have postoperative hypoalbuminemia. The mean ages of with postoperative hypoalbuminemia group and without postoperative hypoalbuminemia group were 47.64 ± 1.42 years and 44.43 ± 2.58 years, respectively (Table 1). The clinical characteristics with statistical significance among the with and without postoperative hypoalbuminemia groups are listed as: operation time (P < 0.001), operation blood loss (P = 0.009), preoperative serum albumin (P < 0.001), preoperative CRP (P = 0.001), and preoperative ESR (P = 0.027) (Table 1).

By consulting the clinical data, the average albumin of each day among the earliest 5 days after operation of 166 patients are calculated: the first day after the operation is 33.9 ± 3.7 g, second day after the operation is 33.7 ± 3 g, third day after the operation is 32.7 ± 3.9 g, fourth day after the operation is 33.2 ± 3.8 g, fifth day after the operation is 35.1 ± 3.6 g. Postoperative serum albumin change trend 5 days after an operation is shown in Figure 1.

Univariate logistic regression analysis found that BMI, pulmonary tuberculosis, operation time, operation blood loss, preoperative lymphocytes, preoperative serum albumin, preoperative CRP, and preoperative ESR are risk factors (Table 2). Multivariate logistic regression analysis was used on the above significant risk factors found that pulmonary tuberculosis, preoperative serum albumin, and operation time are independent risk factors of the postoperative hypoalbuminemia’s occurrence (Table 3). ROC curve showed that the cutoff value of preoperative serum albumin was 40 g/L (sensitivity: 88.6%, specificity: 60.3%) and operation time was 181 min (sensitivity: 66.4%, specificity: 68.6%) (Figure 2).

Multivariate logistic regression analysis was carried out on the significant findings in univariate analysis and showed 3 clinical characteristics namely pulmonary tuberculosis, preoperative serum albumin, and operation time were significant predictors of STB postoperative hypoalbuminemia’s occurrence (Table 3). According to the OR value, pulmonary tuberculosis (OR = 0.270) was assigned as 1-point, preoperative serum albumin (OR = 0.754) was assigned as 2 points, and operation time (OR = 1.017) was assigned as 3 points (Table 4). ROC curve showed that the diagnostic threshold score of the scoring scale was 4 points (sensitivity: 85.5%, specificity: 62.9%) (Figure 3).

The scoring scale that was made by logistic regression was applied to the 102 cases in the validation set. A comparison of the results of the score scale on the derivation set and validation set was listed in Table 5. Based on the threshold score of 4 points, the sensitivity and specificity of the score for predicting STB postoperative hypoalbuminemia were 51.9 and 91.4% in the derivation set, respectively, 63.6 and 86.1% in the validation set (Table 5).

Applying the scoring scale on 166 patients to divide into 2 groups, respectively (score ≤3 points group and score ≥4 points group; preoperative albumin value ≤39 g/L groups and ≥40 g/L group) and get the mean value of preoperative serum albumin, postoperative lowest albumin, and postoperative albumin loss, respectively in each group (Table 6). The postoperative albumin changing trend in the earliest 5 days after surgery in both high-risk group and low-risk group has been shown in Figure 4.

Combining the diagnostic threshold of hypoalbuminemia and respective average decreased albumin value in the 2 groups, we deduced the recommended preoperative serum albumin value of the patients with STB (Table 7).

The proposal of the simple scoring scale is helpful for clinicians to predict whether hypoalbuminemia will occur in patients with thoracic and lumbar tuberculosis after the operation and provide support for whether appropriate treatment measures can be taken to prevent the occurrence of hypoalbuminemia after the operation. Yet, there is no such predictive model of postoperative hypoalbuminemia in patients with STB. Our study is of pioneering significance. The scale is simple and easy to execute and will not add additional workload to clinicians. The specificity of the scoring scale in the derivation set and validation set was, respectively at 91.4% and 86.1%, and both data have confirmed the specificity of the scale is high, which means the patients in the high-risk group authentically have a high incidence to suffer hypoalbuminemia after the operation. The high specificity of the scoring scale brings us new questions like whether patients in the high-risk group can be treated in advance to reduce the occurrence of postoperative hypoalbuminemia, which is the further research direction of our group.

Our score scale also has some unsatisfactory aspects. The sensitivity of the scoring scale in the derivation set and validation set was, respectively 51.9 and 63.6%, which suggests that the missed diagnosis rate of the simple score scale is high. The possibility of hypoalbuminemia after operation in the low-risk group should not be ignored, thus, it is still necessary to pay close attention to the postoperative albumin value of the patients in this group. Due to the limitation of sample size and clinical feature integrity, there is still room for further improvement of our scoring scale, and there may be some independent risk factors for postoperative hypoalbuminemia that have not been revealed.

For more than 50 years, hypoalbuminemia has been associated with increased morbidity and mortality after major abdominal surgeries. Bendersky et al. determined that a threshold preoperative serum albumin of ≥3.9 mg/dL is associated with improved outcomes in elective colorectal surgery patients (34, 35). Similarly, we believed that it is of great clinical significance to explore the appropriate preoperative albumin level in patients with STB, for this consideration, we divided patients with thoracic and lumbar tuberculosis into the low-risk group and high-risk group according to the scoring scale and obtained the postoperative albumin loss values of the two groups. Combined with the diagnostic threshold of hypoalbuminemia: 35 g/L, we proposed the preoperative albumin recommended values for two groups of patients: high-risk group: 44 g/L and low-risk group: 40 g/L. Our study reveals that preoperative albumin level is an independent risk factor for postoperative hypoalbuminemia, which is more likely to occur when the preoperative albumin value is less than 40 g/L. This value coincides with the preoperative albumin recommended value of the low-risk group, which further confirms the rigor of our research results.

For high-risk patients whose preoperative albumin value did not reach the recommended value, the probability of postoperative hypoalbuminemia is very high, so we strongly recommend active treatment. Preoperative nutritional maneuvers play an important role in reducing postoperative impaired healing, morbidities, and mortalities in patients with STB (1, 21). We recommend taking active treatment for this kind of patient, such as supplementing albumin in advance, enhancing the preoperative nutrition, choosing the minimally invasive and short-duration surgical approach. However, for low-risk patients whose preoperative albumin value reached the recommended value, we hold the opinion that it is still necessary to pay close attention to the postoperative albumin change, but there is no need for active preoperative intervention. For some patients whose operation time is hard to predict due to the complex clinical conditions, in consideration of the maximum weight of surgical time on the scoring scale and the safety of postoperative albumin level, we regard the operation time of this kind of patient as greater than 181 min.