In the current study the prevalence of fatty liver was 38.9 % (n = 35) out of 90 obese children and adolescents and most of them having mild degree of fatty liver infiltration. This prevalence is lower in comparable to that reported in Jain et al. (62.5%) ]14[ but it agreed with a pediatric autopsy study conducted in 2006 by Schwimmer and colleagues found that the NALFD prevalence range from 9.6% in normal weight subjects to 38% in obese children and adolescents ]15[. However, it remains difficult to compare the prevalence in various populations as the published data differ regarding their study design, sample selection, diagnostic modality used to define fatty liver and the age, sex, and ethnicity of the study population.
Both BMI and WC noted to be higher in NAFLD group; moreover, elevation in BMI was a significant predictor of fatty liver disease. A study by Hagström and colleagues showed that high BMI in adolescents is a risk factor of severe liver disease later in life with 5% increased risk per 1 kg/m2 increase in BMI ]16[, in addition it was demonstrated that increased abdominal obesity lead to higher risk of fatty liver due to accumulation of lipid in hepatocytes ]17[, furthermore Dâmaso et al. showed that every 1 cm increase in WC is associated with two-folds greater risk of NAFLD in obese children and adolescents ]18[
In the present study significant dyslipidemia (lower HDL-c, Higher triglyceride, and total cholesterol levels) occurs in NAFLD obese children. In multiethnic study on children with NAFLD and according to pediatric cutoff values, the prevalence of elevated triglyceride, non-HDL cholesterol and low HDL-c was 77, 58 and 88% respectively ]19[, in contrast to our findings Gupta et al. showed that lipid levels were not statistically significantly different in the children with and without NAFLD ]3[
In our study, we found that the calculated HOMA-IR score is significantly higher in NAFLD group (6.4 ± 2.6) and it was a good predictor for NAFLD in multivariate logistic regression analysis, also 88.6% of our NAFLD patients had insulin resistance. Significant elevation of HOMA-IR in obese children with fatty liver disease has been reported in several studies ]20, 21[. Furthermore, in a study by Schwimmer et al. on 43 children with biopsy-proven NAFLD, concluded that IR markers (HOMA-IR and Quantitative Insulin Sensitivity Check Index QUICKI) were correlated with severity of liver pathology ]22[. These findings explained by the fact that IR result in increased lipolysis and free fatty acid influx with accumulation of TG within the hepatocyte ]23[. Moreover, it leads to hepatic fibrosis by increasing oxidative stress and fatty acid β-oxidation ]22[. In our study ROC analysis of HOMA-IR cutoff value 3.15 showed sensitivity 88.6% and specificity 72.7% in predicting NAFLD. This was concordant with Salgado et al., who stated that HOMA-IR values above or equal to 2.0 or 2.5 show enhanced diagnostic value in distinguishing non-alcoholic fatty liver disease carriers from control group individuals with sensitivity 85%, specificity 83% and Sensitivity 72%, specificity 94% respectively ]24[. A recent joint European practice guideline for NAFLD ]25[ concluded: ‘HOMA-IR provides a surrogate estimate of insulin resistance in persons without diabetes and can therefore be recommended’.
Metabolic syndrome has been diagnosed in 68.6% of NAFLD patients compared with 14.5% of NAFLD-free patients and this is due to the fact that although NAFLD is not traditionally part of the MetS definition, it is widely considered to be the hepatic manifestation Metabolic syndrome. In a case-control study of 150 obese children with biopsy-proven NAFLD and 150 without, children with MetS had five times the risk of developing NAFLD as obese children without MetS ]26[. In addition, Fu et al. found that the incidence of NAFLD reached 84.61% among 221 obese children with MetS, and this suggests that NAFLD may be an early stage mediator for the prediction of MetS ]27[. Another study on 254 biopsy-confirmed NAFLD showed that the diagnosis of MetS is a good predictor not only of the severity of hepatic steatosis but also of the degree of fibrosis ]28[.
The main and inexpensive screening test for NAFLD is alanine amino transferase. Mild elevation of serum aminotransferase levels is seen in patients with NAFLD, but liver enzymes may be normal in up to 78% of patients ]29[. This is concordant with our results which demonstrated that only 14.2% of children with NAFLD had abnormal ALT. however we found that the mean ALT was significantly elevated in NAFLD group 46.3 ± 8.9. Kim et al. stated that the high ALT level was identified as the most critical factor in NAFLD risk. But high ALT is not a definite NAFLD indicator, nor is high ALT frequently seen in NAFLD patients. A serum ALT of more than 40 IU/L is corresponding to a NAFLD probability of < 0.6. This result shows that high ALT alone does not accurately predict the existence of NAFLL. In addition to serum aminotransferases, additional markers are therefore necessary for accurate evaluation of NAFLD ]30[
One of the limitation of this study is the diagnosis of NAFLD is based on ultrasound imaging which although approved as a safe, inexpensive and non-invasive test with sensitivity y ranging from 60–96% and a specificity ranging from 84–100% ]5[, however it cannot replace liver biopsy as a gold standard for diagnosis which unfortunately carries risk of complications and often not accepted by the parents