Background <p>While visceral adiposity and lipid dysregulation are established drivers of metabolic dysfunction-associated steatotic liver disease (MASLD), the clinical utility of the lipid accumulation product (LAP) for identifying prevalent MASLD in patients with type 2 diabetes mellitus (T2DM) remains insufficiently characterized. This study aimed to characterize the dose-response relationship between LAP and MASLD in T2DM, establish optimal sex-specific diagnostic thresholds, and evaluate its clinical net benefit to guide non-invasive screening.</p> Methods <p>This study included 495 inpatients with T2DM. log₁₀LAP was prioritized using the Boruta algorithm. Diagnostic cut-offs were determined via ROC analysis. The mathematical reliability of these thresholds was evaluated using 1,000-run stratified bootstrapping (internal validation), while the biological generalizability of LAP was further examined in an independent NHANES cohort (external validation). The dose–response relationship was characterized by restricted cubic splines (RCS). Clinical utility and stability were assessed using decision curve analysis (DCA) and subgroup analyses.</p> Results <p>Through a systematic feature-selection approach using the Boruta algorithm, log₁₀LAP was objectively identified as the most robust indicator for MASLD.log₁₀LAP was independently associated with MASLD (OR 1.83, 95% CI 1.43–2.35). Optimal sex-specific cut-offs were 20.4 for men and 27.0 for women, yielding a positive predictive value of 85.93%. RCS analysis revealed a significant linear association, with MASLD probability increasing monotonically with log₁₀LAP. DCA demonstrated a consistently higher net benefit for the LAP-based model over the “screen-all” strategy at threshold probabilities &gt; 0.20. Subgroup analyses confirmed robustness across age and BMI strata, with the highest discriminative power in patients aged &lt; 55 years (AUC 0.855) and reliable performance in non-obese individuals (AUC 0.711). External analysis in the NHANES cohort (<i>N</i> = 630) demonstrated consistent independent associations between LAP and MASLD risk (<i>P</i> &lt; 0.05).</p> Conclusions <p>log₁₀LAP is a robust linear predictor of MASLD in T2DM. Implementing tailored thresholds provides superior diagnostic precision and clinical net benefit, particularly for younger and non-obese populations, supporting its use as a prioritized non-invasive screening tool.</p> Graphical abstract <p></p>