BackgroundNonalcoholic fatty liver disease (NAFLD) is the most frequent disease associated with abnormal liver tests that is characterized by a wide spectrum of liver damage, ranging from simple macro vesicular steatosis to steatohepatitis (NASH), cirrhosis or liver carcinoma. Liver biopsy is the most precise test to differentiate NASH from other stages of NAFLD, but it is an invasive and expensive method. This study aimed to create a clinical laboratory score capable of identify individual with NASH in severely obese patients submitted to bariatric surgery.MethodsThe medical records from 66 patients submitted to gastroplasty were reviewed. Their chemistry profile, abdominal ultrasound (US) and liver biopsy done during the surgical procedure were analyzed. Patients were classified into 2 groups according to liver biopsy: Non-NASH group - those patients without NAFLD or with grade I, II or III steatosis; and NASH group - those with steatohepatitis or fibrosis. The t-test was used to compare each variable with normal distribution between NASH and Non-NASH groups. When comparing proportions of categorical variables, we used chi-square or z-test, where appropriate. A p-value < 0.05 was considered statistically significant.Results83% of patients with obesity grades II or III showed NAFLD, and the majority was asymptomatic. Total Cholesterol (TC)≥200 mg/dL, alanine aminotransferase (ALT) ≥30, AST/ALT ratio (AAR)≤ 1, gammaglutaril-transferase (γGT)≥30 U/L and abdominal US, compatible with steatosis, showed association with NASH group. We proposed 2 scores: Complete score (TC, ALT, AAR, γGT and US) and the simplified score, where US was not included. The combination of biochemical and imaging results improved accuracy to 84.4% the recognition of NASH (sensitivity 70%, specificity 88.6%, NPV 91.2%, PPV 63. 6%).ConclusionAlterations in TC, ALT, AAR, γGT and US are related to the most risk for NASH. The combination of biochemical and imaging results improved accuracy to 84.4% the recognition of NASH. Additionally, negative final scores exclude the presence of an advanced illness. Using this score, the severity of fatty liver infiltration would be predicted without the risks associated with hepatic biopsy.