Prediction of Non-Alcoholic Fatty Liver Disease (NAFLD) in Both Lean and Obese Patients Utilizing the Waist to Height Ratio (WHR) and Fatty Liver Index (FLI)

Background: Non-alcoholic fatty liver disease (NAFLD) is a burgeoning health issue with a global prevalence that mirrors the rise in obesity and metabolic syndrome. Non-invasive diagnostic indices like the Waist to Height Ratio (WHtR) and the Fatty Liver Index (FLI) are crucial for early detection and management, offering an alternative to the invasive liver biopsy. These indices are particularly pertinent for populations with distinctive body compositions, such as those seen in Asian countries, where traditional measures like Body Mass Index (BMI) may not accurately reflect metabolic risk. Objective: To evaluate the efficacy of WHtR and FLI as non-invasive diagnostic tools for NAFLD in both lean and obese populations, and to identify the most reliable indicator for predicting the presence of fatty liver disease across different body compositions. Methods: This cross-sectional study was approved by the Ethical Review Board (ERC-771) and conducted at the Sindh Institute of Urology and Transplantation. It included 757 participants aged 18-70 years, with 559 lean and 298 obese individuals based on BMI classifications. Exclusion criteria included other forms of hepatitis, use of steatogenic medication, and significant gastrointestinal disorders. Diagnostic measures included abdominal ultrasonography performed by an expert radiologist and calculation of WHtR and FLI. Statistical analyses were performed using SPSS version 25, and diagnostic accuracy was assessed through sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and Area Under the Receiver Operating Characteristic (AUROC) curves. Results: Fatty liver was detected in 49% of obese patients and 33% of lean patients. The obese cohort demonstrated a WHtR >0.63 with a diagnostic accuracy of 94.63%, whereas the FLI had a diagnostic accuracy of 83.6% for a cutoff >74. In lean patients, FLI >16.5 was more predictive of NAFLD with a diagnostic accuracy of 96.96%, as opposed to WHtR, which was less effective. The AUROC for WHtR and FLI in obese patients was 0.847 and 0.704, respectively, while in lean patients, the AUROC for FLI was 0.875, suggesting superior diagnostic performance over WHtR. Conclusion: The study confirms that WHtR and FLI are valuable non-invasive tools for predicting NAFLD, with WHtR being more effective in obese patients and FLI showing greater reliability in lean patients. These findings highlight the need for tailored approaches in diagnosing NAFLD according to body composition. Further large-scale, multicentric research is needed to generalize these diagnostic cut-offs.