The medical records of men and women aged 19 years or older who underwent abdominal CT examination at the University Hospital Health Promotion Center from March 2012 to October 2019 were retrospectively reviewed. Patients with incomplete records, acute infectious diseases, cancer, and findings suggestive of cancer were excluded, and 1,059 participants were included in the final analysis. Among them, 852 participants who had all the records of the indicators for calculating the FLI were analyzed. This study followed the ethical standards established in the Declaration of Helsinki. Consent was not required from all participants. We only reviewed patient charts for this study, we pledged that we would not use the information for anything other than research purposes. Also we reviewed the chart, which provided only the number of participants instead of their names. This was approved by the institutional review board of the Wonkwang University Hospital (ARB Approval No. 2020-06-002-002).
MAFLD was diagnosed based on one of the following criteria:
Overweight or obesity (defined as BMI of ≥ 23 kg/m2) and fatty liver on a CT scan.
Lean/normal weight (defined as BMI of < 23 kg/m2) and fatty liver on a CT scan with at least two metabolic risk abnormalities:
• WC of ≥ 102/88 cm in Caucasian men and women (or ≥ 90/80 cm in Asian men and women).
• Blood pressure ≥ 130/85 mmHg or receiving specific drug treatment.
• Plasma triglycerides level of ≥ 150 mg/dL (≥ 1.70 mmol/L) or receiving specific drug treatment.
• Plasma HDL cholesterol level of < 40 mg/dl (< 1.0 mmol/L) for men and < 50 mg/dL (< 1.3 mmol/L) for women or receiving specific drug treatment.
• Prediabetes (i.e., fasting glucose levels of 100–125 mg/dL [5.6–6.9 mmol/L], 2-h post-load glucose levels of 140–199 mg/dL [7.8–11.0 mmol] or hemoglobin (Hb) A1c level of 5.7–6.4% [39–47 mmol/mol])
• Homeostasis model assessment of insulin resistance scores of ≥ 2.5.
• Plasma high-sensitivity C-reactive protein levels of > 2 mg/L.
Diabetes mellitus (according to widely accepted international criteria) and fatty liver on a CT scan.
SOMATOM definition (Siemens Medical Solutions, Forchheim, Germany) was used for CT scans of the abdominal pelvis, and image readings were performed by a radiologist. To avoid examiner bias, all data were reconfirmed by a medical imaging specialist who was blinded to the patient's characteristics, medical history, and research objectives. Fatty liver was diagnosed when the liver attenuation value was < 40 Hounsfield units (HU) or < 10 HU compared to that of the spleen.
WC measured by the measurer and examinee using a waist tape was prone to large errors. Therefore, WC was measured according to the level recommended by the World Health Organization at the mid (half) point between the lowest rib and iliac ridge on CT images.
Anthropometric assessment and blood test
The height and weight were measured using an automatic height scale. BMI was used to check for obesity and overweight. BMI was calculated by dividing body weight by height squared (kg/m2). According to the Asian criteria, a BMI of ≥ 23 was defined as overweight, and a BMI of ≥ 25 was defined as obesity. After keeping the blood pressure stable for at least 10 mins, an automatic sphygmomanometer was used to measure the blood pressure, and the average of the two measurements was recorded.
After fasting for > 8 h, blood was collected from a vein and was immediately sent to the Neodine Lab for liver function tests, complete blood cell count, blood lipid level, blood sugar level, and serum tests. Fasting blood sugar (FBS), insulin, total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), alanine aminotransferase (ALT), aspartate amino transferase (AST), gamma-glutamyl transpeptidase (GGT), uric acid (UA), creatinine (Cr), highly sensitive C-reactive protein (hs-CRP), white blood cell (WBC), hemoglobin, and vitamin D concentrations were measured.
Clinical and lifestyle assessments
The experts at the health screening center used self-questionnaires to examine participants’ medical history and lifestyle. Participants who were diagnosed with type 2 diabetes or receiving drugs were recorded. Participants were classified as smokers and non-smokers, and those who smoked continuously for the past two years were classified as smokers. If they consumed a meaningful amount of alcohol at least once a week, alcohol consumption was marked as 'yes'.
FLI = (e(0.953×ln(TG) + 0.139×BMI + 0.718×ln(GGT) + 0.053×WC − 15.745))/(1 + e(0.953×ln(TG) + 0.139×BMI + 0.718×ln (GGT) + 0.053×WC − 15.745))×100
TG, triglyceride (mg/dL); GGT, γ-glutamyl transferase (U/L); WC, waist circumference (cm). BMI was calculated by dividing body weight by the square of height (kg/m2) .
SPSS for Windows (version 26.0; SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. A comparative analysis between non-continuous variables was performed using the chi-squared test.
The AUROC curve was used to verify the effectiveness of FLI as a predictive index for MAFLD. The method developed by DeLong et al. was used to compare the FLI and AUROC.
FLI's ability to distinguish between participants with and without MAFLD was assessed using the ROC curve. The sensitivity of the infinite determination threshold of FLI was expressed as a false positive rate, and the relevant area under the curve (AUC) was calculated. The lower limit of the AUC was considered as 0.5, and the area > 0.5 demonstrates the effectiveness of FLI in distinguishing patients with and without MAFLD. The optimal cutoff point for FLI was determined using the maximum value of Youden's J statistic [max (J = sensitivity + specificity − 1)]. The value of FLI, which corresponds to the maximum value of the Youden index, was considered the best reference point for FLI .