Alanine Aminotransferase (ALT), often referred to by its older name, Serum Glutamic Pyruvic Transaminase (SGPT), is a standard marker included in a comprehensive metabolic panel or liver panel. An elevated level often prompts concern about liver health. The blood test measures the concentration of this enzyme circulating in the blood, which provides a direct indication of potential injury or inflammation within the liver.
The Function of Alanine Aminotransferase (ALT/SGPT)
Alanine Aminotransferase is a protein that serves as a catalyst for biochemical reactions inside cells. Its primary location is within the hepatocytes, the main cells that make up the liver, although smaller amounts are also found in the kidneys, heart, and skeletal muscles. The enzyme’s main biological role is linked to protein metabolism, facilitating the transfer of an amino group from L-alanine to alpha-ketoglutarate. This results in the production of pyruvate and L-glutamate, compounds the body uses for energy production.
Under normal conditions, ALT remains contained within the liver cells, and only a tiny amount naturally cycles through the bloodstream. When the liver sustains damage from injury, disease, or inflammation, the cell walls of the hepatocytes become compromised. This cellular damage causes the internal contents, including the ALT enzyme, to spill out into the bloodstream. The blood test detects this sudden, abnormal increase in circulating ALT, which signals hepatocellular injury.
Interpreting Elevated ALT/SGPT Results
A blood test result is compared against a laboratory’s established reference range, which defines the upper limit considered normal. For men, the upper limit is often cited around 33 to 35 International Units per liter (IU/L), and for women, this range is slightly lower, around 25 IU/L.
The magnitude of the elevation helps guide the diagnostic process, as a higher level usually correlates with more acute or extensive liver damage. A mildly elevated level, perhaps less than five times the upper limit of normal, often suggests chronic conditions like fatty liver disease. Conversely, severe elevations, which can be ten times the upper limit or more, are commonly seen in cases of acute viral hepatitis or drug-induced liver injury.
A high ALT level is not a specific diagnosis itself but rather a signpost pointing toward liver injury. The liver can sustain significant damage before any symptoms become noticeable, making the ALT test a valuable screening tool.
Primary Medical Causes of High ALT Levels
The leading cause of persistently elevated ALT levels is Metabolic dysfunction-associated Steatotic Liver Disease (MASLD), formerly known as Non-Alcoholic Fatty Liver Disease. This condition involves the accumulation of excess fat within the liver cells, associated with metabolic factors like obesity, type 2 diabetes, and high cholesterol. The presence of this fat causes chronic inflammation, leading to a mild to moderate elevation of the enzyme.
Another significant group of causes involves the use of certain medications, which can induce liver injury. Common over-the-counter pain relievers like acetaminophen, when taken in excessive doses or combined with alcohol, are well-known to cause severe toxicity. Similarly, prescription drugs such as some cholesterol-lowering statins, certain antibiotics, and various herbal and dietary supplements can stress the liver and lead to elevated ALT readings.
Acute viral infections, particularly Hepatitis A, B, and C, trigger an immune response that attacks and destroys liver cells. In these cases, destruction is often widespread and rapid, resulting in some of the highest recorded ALT levels, sometimes reaching thousands of units per liter. Chronic, heavy alcohol consumption also causes liver inflammation and damage, resulting in Alcohol-Related Liver Disease. While ALT is elevated, a higher level of the related enzyme AST is often more characteristic.
Less common causes include genetic conditions such as Hemochromatosis, which causes iron overload, and Wilson’s disease, involving copper accumulation. Autoimmune conditions, where the body’s immune system attacks liver tissue, or non-liver issues like severe muscle injury or certain thyroid disorders, can also cause the ALT level to rise.
Follow-Up Testing and Management
An elevated ALT level is a prompt for further investigation, not a final conclusion about liver health. The next step typically involves ordering a more comprehensive liver function panel, which includes measurements of other enzymes like Aspartate Aminotransferase (AST) and Alkaline Phosphatase (ALP), as well as bilirubin. The patterns and ratios between these different markers help narrow down the potential cause of the injury.
The diagnostic process also frequently includes imaging tests, such as an abdominal ultrasound, to visually assess the liver for signs of fat buildup, scarring, or obstruction. Specialized non-invasive tests, like transient elastography, may be used to measure the stiffness of the liver tissue, which helps determine the degree of existing fibrosis or scarring.
Management focuses on addressing the underlying cause identified through the workup. For elevations linked to MASLD, the primary course of action involves sustained lifestyle modifications, including dietary changes, increased physical activity, and weight loss. If a medication is suspected, the physician may discontinue or replace the drug. Monitoring the trend of the ALT level over time is important, as a steady decline back toward the normal range indicates that the liver is healing and the intervention has been successful.