The term fatty liver disease, now often referred to as metabolic dysfunction-associated steatotic liver disease (MASLD), describes a condition where excess fat (steatosis) accumulates in the liver cells. This fat buildup is increasingly common worldwide, affecting a significant portion of the population, especially those with obesity and type 2 diabetes. People often rely on standard blood tests to gauge liver health, assuming a normal result means the liver is functioning perfectly. However, this reliance can be misleading, as the presence of fat in the liver does not always trigger the typical warning signals seen in routine lab work.
What Liver Enzymes (ALT and AST) Indicate
The standard blood tests used to monitor liver function measure the levels of two enzymes: Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST). These enzymes are normally located inside liver cells, where they play a role in the metabolism of amino acids. ALT is highly specific to the liver, while AST is also found in other organs, including the heart, muscles, and kidneys.
When liver cells are damaged or inflamed, their membranes become compromised, causing these enzymes to leak into the bloodstream. Elevated levels of ALT and AST are therefore viewed as a marker of acute cellular injury or ongoing inflammation. Doctors assess these readings to determine if there is an active problem, such as viral hepatitis or drug-induced liver injury.
The enzyme elevation generally reflects the severity of the acute damage occurring. However, a significant limitation is that these markers only signal active cell death, which is not always present in the early or mild stages of chronic liver disease.
The Silent Reality: Fatty Liver Disease Despite Normal Enzyme Levels
Yes, fatty liver can exist with normal enzyme levels, and this silent presentation is quite common. Studies indicate that a large number of individuals with confirmed fatty liver disease, potentially up to 80%, may have persistently normal ALT and AST values. This disconnect occurs because the simple accumulation of fat (steatosis) often does not cause enough immediate, widespread damage to the liver cells to release a large quantity of enzymes.
In the early stages, inflammation may be too mild or localized to produce a sustained elevation. Enzymes can also fluctuate, meaning a single blood test may catch the values during a period of normalcy. Furthermore, some individuals with advanced disease, including significant scarring (fibrosis), can still maintain enzyme levels within the normal range.
Relying on a normal ALT or AST result can give a false sense of security regarding the absence of MASLD. The degree of enzyme elevation does not perfectly correlate with the amount of fat in the liver or the extent of underlying fibrosis. This situation underscores why MASLD is often called a “silent disease,” as it can progress even when routine lab work appears unremarkable.
The standard upper limits of normal for ALT and AST may also be set too high, potentially masking low-level liver injury in certain high-risk populations. For people with risk factors such as obesity, diabetes, or metabolic syndrome, a result at the high end of the normal range may still warrant further investigation. These metabolic risk factors are a stronger indicator of potential fatty liver disease than a slightly elevated enzyme level in isolation.
Confirming a Diagnosis When Enzymes Are Unremarkable
Since the standard blood panel is an insufficient screening tool for many people with MASLD, confirmation relies on alternative methods, particularly imaging techniques. The most common first step is an abdominal ultrasound, which uses sound waves to visualize the liver and detect fat infiltration. Ultrasound is widely available and low-cost, making it the preferred initial screening tool, though it is not highly sensitive for very small amounts of fat.
If fat is detected, or if a doctor suspects the disease based on clinical risk factors, non-invasive tools assess severity. Transient Elastography (FibroScan) is a specialized ultrasound technique that measures the stiffness of the liver. Increased stiffness indicates the presence of fibrosis or scarring, which is the most significant predictor of future liver complications.
Magnetic Resonance Imaging-Proton Density Fat Fraction (MRI-PDFF) can accurately quantify the percentage of fat within the liver. These advanced tools allow for precise monitoring without the risks associated with invasive procedures. While liver biopsy remains the gold standard for staging the disease, it is generally reserved for cases where there is a high suspicion of advanced fibrosis or when other diagnoses cannot be excluded.