Does fatty liver disease (Steatosis) always result in elevated Alanine Transaminase (ALT) levels?

From the Guidelines

Fatty liver does not always mean elevated ALT, as many individuals with fatty liver disease can have normal ALT levels, especially in early stages. While ALT elevation is common in fatty liver disease, it is an imperfect marker for diagnosis, as it only suggests liver inflammation or injury when elevated 1. According to the most recent study published in the Journal of the American College of Radiology in 2023, normal ALT levels are 29 to 33 IU/L in men and 19 to 25 IU/L in women 1. The severity of fatty liver doesn't necessarily correlate with ALT levels either, as some people with severe fatty liver may have normal ALT, while others with mild fatty liver might have elevated ALT 1.

Key Points to Consider

• Fatty liver disease is a spectrum of fat deposition and hepatic inflammation, and ALT elevation is not always present 1
• Imaging tests like ultrasound, CT, or MRI are typically used to diagnose fatty liver, regardless of ALT levels 1
• A comprehensive evaluation including imaging and possibly other liver function tests is more informative than relying solely on ALT levels 1
• The most common causes of fatty liver disease are nonalcoholic fatty liver disease (NAFLD) and alcohol-induced steatosis/steatohepatitis, with NAFLD being the most common liver disease in first-world countries 1

Clinical Implications

• A normal ALT level does not rule out fatty liver disease, and further evaluation with imaging tests is necessary for diagnosis 1
• Elevated ALT levels should be investigated further to determine the underlying cause, which may include fatty liver disease, viral hepatitis, or other liver injuries 1
• A comprehensive approach to diagnosis and management is essential to improve patient outcomes and reduce morbidity and mortality associated with fatty liver disease 1

From the Research

Fatty Liver and Elevated ALT

• Fatty liver, also known as nonalcoholic fatty liver disease (NAFLD), is a condition where there is an accumulation of excess fat in the liver cells [(2,3,4)].
• NAFLD can be divided into two forms: nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH) [(2,3,4)].
• Elevated alanine aminotransferase (ALT) is often associated with liver damage or disease, but it is not a definitive indicator of fatty liver [(5,6)].
• Studies have shown that patients with NAFLD may have normal or mildly elevated ALT levels, and that the upper normal limit of ALT may not be an accurate indicator of liver disease 5.
• In fact, one study found that reducing the upper normal limit of ALT from 45 IU/L to 30 IU/L for men and from 34 IU/L to 19 IU/L for women did not improve the detection of significant liver disease 5.

Clinical Presentation and Diagnosis

• NAFLD is often asymptomatic and may be diagnosed incidentally during routine health check-ups or when liver enzymes are found to be elevated [(2,3)].
• The diagnosis of NAFLD is typically made based on a combination of clinical, laboratory, and imaging findings, including liver biopsy [(2,3,4)].
• Liver function tests, including ALT and aspartate aminotransferase (AST), may be used to monitor liver health and detect potential liver damage, but they are not always reliable indicators of NAFLD [(5,6)].

Risk Factors and Associations

• NAFLD is associated with several risk factors, including obesity, metabolic syndrome, and type 2 diabetes mellitus [(2,3,4)].
• Patients with type 1 diabetes mellitus may also be at risk for NAFLD, particularly if they have elevated ALT levels 6.
• The presence of NAFLD may increase the risk of cardiovascular disease, cancer, and end-stage liver disease [(2,4)].