Alanine Aminotransferase (ALT) is an enzyme measured as part of a Liver Function Panel (LFP) or Liver Function Tests (LFTs). This blood test provides an indirect look into the health of the liver, which is responsible for vital metabolic and detoxification processes. The ALT test screens for signs of liver cell damage or inflammation. A result outside the expected range prompts a healthcare provider to investigate further.
Understanding ALT and Liver Function
ALT is a type of enzyme known as a transaminase, which assists in converting amino acids into energy. Specifically, it catalyzes the transfer of an amino group from alanine to alpha-ketoglutarate, producing pyruvate and glutamate. The enzyme is found in high concentrations within the cytoplasm of liver cells, known as hepatocytes.
Normally, only small, trace amounts of ALT are present in the bloodstream because the enzyme is contained within these cells. However, when liver cells are damaged due to inflammation, injury, or disease, the cell membranes become compromised and leak their contents. This leakage releases the stored ALT into the general circulation, causing a measurable increase in the blood level. Therefore, an elevated ALT level in a blood test is a strong indicator of hepatocellular damage.
Defining the Normal Range for Women
The normal range for ALT is expressed in Units per Liter (U/L) of blood, though this range varies slightly between different laboratories. The conventional upper limit of normal for adult women is generally cited as 35 to 45 U/L. However, many liver specialists suggest a more stringent cutoff, sometimes recommending a level no higher than 19 to 25 U/L to better identify early signs of subtle liver injury.
The range for women is typically lower than that for men, a difference largely attributed to physiological factors. Women generally have less overall skeletal muscle mass than men, and since ALT is also present in muscle tissue, this contributes to a naturally lower baseline level. Hormonal differences and variations in average body size also play a role. Always refer to the specific reference range provided on your laboratory report.
Common Causes of Elevated ALT
An elevated ALT result prompts investigation into conditions that cause damage to liver cells. Mild elevations, often defined as less than twice the upper limit of normal, are frequently linked to lifestyle factors. The leading cause of persistently mildly elevated ALT is Metabolic dysfunction-associated Steatotic Liver Disease (MASLD), formerly known as Non-Alcoholic Fatty Liver Disease (NAFLD). This condition involves the accumulation of excess fat within the liver cells, often associated with obesity, type 2 diabetes, and high cholesterol.
Another frequent cause is the use of certain medications, which can lead to drug-induced liver injury. Common culprits include over-the-counter pain relievers like acetaminophen, especially when taken in high doses, and various prescription drugs, such as certain statins and antibiotics. Even herbal supplements and intense, recent physical exertion can cause a temporary, mild rise in ALT levels by releasing the enzyme from muscle tissue.
More significant elevations, often three to ten times the upper limit, can point toward more acute liver inflammation. Excessive alcohol consumption is a well-known cause, leading to alcoholic liver disease, which includes fatty liver, hepatitis, and cirrhosis. Acute viral infections, such as Hepatitis A, B, or C, cause significant and rapid destruction of hepatocytes, resulting in a substantially high release of ALT into the bloodstream. Less common, but serious, causes of high ALT include autoimmune hepatitis, iron overload (hemochromatosis), and Wilson disease.
Next Steps Following an Abnormal Test
An isolated elevated ALT result is rarely diagnostic on its own, serving instead as a signal for further investigation to pinpoint the underlying issue. The physician typically orders a series of additional blood tests, often called a liver panel, which includes Aspartate Aminotransferase (AST), gamma-glutamyl transferase (GGT), and bilirubin. Analyzing the ratio between ALT and AST, along with other markers, provides specific clues about the type and severity of liver damage.
If the elevation is mild and no clear cause is identified immediately, the first approach is often to repeat the blood test after a period of observation. Lifestyle adjustments are frequently recommended for managing most mild elevations. These modifications include reducing or eliminating alcohol intake, adopting a balanced diet to promote weight reduction if necessary, and engaging in regular physical activity. A healthcare provider must interpret the results in the context of the patient’s full medical history, symptoms, and other test results to determine the appropriate next steps, which may include imaging like a liver ultrasound.