NAFLD is generally suspected when aminotransferase levels are asymptomatically
elevated in an individual with metabolic risk factors (obesity and
diabetes) or when liver imaging (ultrasound, CT, or MRI) obtained for
another reason shows fatty infiltration (Fig. 155-2). The diagnosis of NAFLD
requires that there is no history of previous or ongoing significant alcohol
consumption, no exposure to steatogenic medications, and no evidence of
other causes of liver disease, such as viral hepatitis B or C. Elevated levels
of aminotransferases, although common, are not required for the diagnosis
of NAFLD. In contrast to alcoholic liver disease, ALT levels are higher than
AST levels, but they rarely exceed 250 IU/L. In general, AST and ALT levels
do not have diagnostic or prognostic significance. Mild hyperferritinemia is
common and should not be confused with hereditary hemochromatosis
(Chapter 219). Similarly, low-grade autoantibody (antinuclear antibody,
anti–smooth muscle antibody) positivity is not uncommon and should not
be confused with autoimmune liver disease (Chapter 151). Because steatosis
is common in patients with Wilson’s disease (Chapter 218), serum ceruloplasmin
should be obtained as part of the diagnostic evaluation.
Fatty liver on ultrasonogram has a positive predictive value of only 77%
and a negative predictive value of only 67% when compared with liver biopsy.
Abdominal MRI is more accurate, but its high cost limits its usefulness in
routine practice. Because none of these three tests can differentiate simple
steatosis from NASH nor identify cirrhosis until hepatic fibrosis has caused
overt portal hypertension, liver biopsy is required to establish the presence
of NASH or cirrhosis. Common indications for a percutaneous liver biopsy