Introduction: Many laboratories utilize Friedewald formula (FF) to analyze LDL cholesterol levels of patients including diabetes mellitus (DM). Therefore, it is essential to consider the coherence of results acquired by FF and direct measurement. The number of studies that investigated the effect of lipid parameters, especially TG/HDL cholesterol ratio, on the difference between the two methods is limited. The study was designed to compare LDL cholesterol values obtained by using FF with direct measurement, and to evaluate the relationship between diabetes regulation and lipid profile. Material and Methods: In the cross-sectional study, 529 type 2 DM patients and 1703 non-DM subjects were divided into four groups regarding TG concentrations. Unlike other studies, the study focuses on direct LDL (DLDL) cholesterol levels obtained with the help of different DLDL cholesterol kits (n=20). The correlations were implemented between HbA1c and lipid profiles. Results: It was determined that the bias% was over 10% in 24% of patients with 100-199 mg/dL TG levels. The parameter revealed that the most significant difference and the strongest correlation with HbA1c was TG/HDL cholesterol ratio in patients with type 2 DM. Conclusions: In patients with type 2 DM, even if it was TG <200 mg/dL, LDL calculated with FF should be evaluated together with the TG/HDL cholesterol ratio. Otherwise, direct measurement can be recommended. This ratio is related to diabetes regulation and may be used to monitor patients..