Assessment of Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide. While patients with simple steatosis have excellent long-term prognosis, those with non-alcoholic steatohepatitis (NASH) may progress to cirrhosis, liver failure and hepatocellular carcinoma. NAFLD is also closely associated with metabolic syndrome and cardiovascular events. Therefore, Professor Vincent W.S. Wong, from The Chinese University of Hong Kong, Hong Kong SAR, emphasized that the assessment of NAFLD should focus on (1) establishing the diagnosis and ruling out other causes of abnormal liver function tests, (2) identifying patients who had developed or would develop severe liver injury, and (3) detecting important co-morbid illnesses.

He said that the diagnosis of NAFLD was usually straightforward. By ultrasonographic examination, typical features include bright hepatic echotexture (compared with kidney and/or spleen), deep attenuation and vascular blunting. However, chronic hepatitis C can cause hepatic steatosis, and a patient with fatty liver can have alternative causes of abnormal liver function tests. Therefore, the minimal diagnostic workup should include hepatitis B and C serology and anti-nuclear antibody. He also said patients with NASH were more likely to have type 2 diabetes and obesity. Thrombocytopenia, hypoalbuminemia and signs of portal hypertension may be present in patients with NASH-related cirrhosis. However, none of these features are sensitive for NASH or liver fibrosis. Similarly, although serum alanine aminotransferase is commonly used to monitor patients with chronic liver diseases, it has poor correlation with the severity of NAFLD.

Professor Wong also pointed out that the gold standard for the diagnosis of NASH and assessment of liver fibrosis was liver biopsy at present. However, the procedure carries a small risk of complications, is expensive and may not be acceptable to many patients. Besides, the problem of sampling error is increasingly recognized. Non-invasive tests for NASH and liver fibrosis are urgently needed. Using six clinical parameters (age, hyperglycemia, body mass index, platelet count, albumin, and aspartate aminotransferase-to-alanine aminotransferase ratio), the NAFLD fibrosis score has good negative predictive value for advanced fibrosis in both Caucasians and Chinese. Transient elastography by Fibroscan is another promising non-invasive test for liver fibrosis. It appears to have good accuracy in NAFLD, but failed measurement is more common in obese subjects. For the metabolic assessment, anthropometric measurements include body weight, body height, waist circumference and hip circumference. Since Asians have the same percentage of body fat and develop metabolic complications at a lower body mass index than Caucasians, it is important to use ethnic-specific cutoff values in anthropometric measurements. Other essential tests include blood pressure measurement, fasting glucose, and fasting lipids. Impaired glucose tolerance and undiagnosed diabetes are very common among NAFLD patients. Oral glucose tolerance test should be considered in every NAFLD patient, especially if the fasting glucose exceeds 5.6 mmol/L.