Study design and participants
The present retrospective single-center analysis included data of consecutive patients who were primary diagnosed with AML at Affiliated Ganzhou Hospital of Nanchang University (Jiangxi Province, China) between January 1, 2013, and May 31, 2021. All participants in this study underwent bone marrow (BM) aspiration, and AML diagnosis was confirmed based on two or more ways of morphology, immunology, cytogenetic and molecular (MICM) analysis, according to the World Health Organization (WHO) classification system (version 2016) [12]. This study followed the principles of the Declaration of Helsinki and was approved by the Ethics Review Board of Affiliated Ganzhou Hospital of Nanchang University. Given the retrospective nature of the study and the use of anonymous patient data, the requirement for obtaining informed consent was waived [10].
Patients diagnosed APL were excluded because their management and treatment were quite different from the patients with the other subtype of AML [4, 5]. Patients with a history of other hematological malignancies, such as myelodysplastic syndrome (MDS) or myeloproliferative neoplasms (MPN) e.g., were excluded due to secondary AML,because the level of serum ALB may be affected by the primary disease. Individuals with mixed phenotype acute leukemia (MPAL) and AML-M6, who did not meet the WHO classification criteria (version 2016), were also excluded as they were categorized as non-AML patients from a strict sense [12]. Patients with liver failure or nephrotic syndrome that causes hypoalbuminemia were excluded from the study.
In addition, patients who were aged < 15 years or non-Hakka, did not undergo a serum ALB test in 48 hours of admission, or were lost to follow-up were also excluded; The remaining patients with or without chemotherapy were included in the study. AML patients were divided into four subtypes: AML-M2, AML-M4, AML-M5, and other subgroups in this cohort study. The flowchart of the patient selection process is presented in Fig. 1.
Source of data
Data, including survival status, were collected from the electronic medical record system or via follow-up telephone calls. The baseline examinations included blood and BM parameters. The biomarkers included ALB, glucose (Glu), direct bilirubin (DBIL), creatine kinase isoenzyme MB, myoglobin (Myo), serum ferritin (SF), fibrinogen (Fib), BM blast e.g. [10]. All laboratory data included measurements performed within the first 48 hours of admission to reduce the probability that serum biomarker levels were affected by anti-leukemia therapy. These parameters comprise routine testing, commonly used to evaluate the patient’s physical condition. Chemotherapy was administered within 60 days of hospitalization, and none of the patients received bone marrow transplantation.
Serum ALB
Serum ALB levels were measured using a biochemical analyzer (AU5800. Beckman Coulter, Inc.) with an albumin determination reagent kit (Bromocresol Green method) (Zhejiang Elekon Biotechnology Co., Ltd), read our previous report [10], in brief. The reference interval for ALB was 35–55 g/L, followed the national standard. Every day, we did internal quality control (IQC) (Bio-Rad Laboratories, Inc. Hercules, CA, USA) with commercially available control materials before testing blood samples. Serum ALB was included in the activities of external quality control (EQA), which was hosted by the National Center for Clinical Laboratories (NCCL) thrice a year, and during this study all criteria for feedback reports were fulfilled. All data from this study, including ALB and other items or parameters, were the preliminary test results of patients after admission due to AML. ALB levels were divided into three groups based on ALB quantiles or two based on its level of 35 g/L.
Outcome
The primary endpoint and outcome of interest were death within 60 days of admission. Collectors of patients’ clinical information at the first diagnosis were blinded to the survival data.
Statistical analysis
This study aimed to observe the impact of ALB on 60-day mortality in patients with AML. The patients were divided into three groups based on ALB quantiles. A descriptive analysis was asked to all participants. Continuous data were expressed as mean and standard deviation or median and interquartile range ([IQR], quartile 1–quartile 3), as appropriate. The categorical variables were expressed as proportions (%). The variables were compared using of chi-square test (categorical variables), one-way analysis of variance (normal distribution), and Kruskal-Wallis (skewed distribution) tests.
Multivariate Cox regression analysis was used to assess the independent association between serum ALB levels and 60-day mortality. An extended Cox model approach was used for models that were adjusted for various covariates. Covariables were chosen on the basis of previous findings and clinical constraints. Or we adjusted for variables, of which the p-values were less than 0.005 for univariate analysis. Survival curves were plotted using of Kaplan-Meier method and were evaluated for statistical significance using log-rank tests. Subgroup analyses were stratified based on the relevant effect covariates. Dummy variables were used to indicate the missing covariancevalues if the missing data variables were greater than 10%. Analyses were stratified according to the results of the univariate analysis (p < 0.005), including sex, age, Glu, Myo level, and chemotherapy, to examine the effect of these factors on the above associations. The likelihood ratio test was used to assess the effect modification according to the respective subgroups using interaction terms between subgroup indicators and ALB. Interactions across subgroups were tested using the likelihood ratio test. All analyses were performed using R 3.3.2 (http://www.R-project.org. The R Foundation) and Free Statistics (version 1.4). Differences with a two-sided P-value of < 0.05 were considered significant [13].