Understanding Liver Values: AST, ALT, GGT, Bilirubin

TL;DR: ALT below 45 U/L (men) or below 34 U/L (women), AST below 35 U/L, GGT below 60 U/L (men) or below 40 U/L (women), bilirubin below 1.2 mg/dl. Mildly elevated values are common and do not automatically mean liver disease. Only the interplay of multiple markers gives a clear picture.

This article is purely informational and does not replace medical advice. It makes no recommendation for the use of any product: intake, dose and therapy should be clarified with a doctor. If liver values are significantly elevated or symptoms are present, seek medical advice.

What Liver Values Actually Show

Liver values measure three distinct functions: ALT and AST signal cell damage, GGT and bilirubin indicate bile obstruction, and albumin plus INR reflect synthetic capacity. A single mildly elevated value rarely means liver disease — only the combination of multiple markers tells the full story.

Liver values are not liver health tests. They measure whether liver cells are being destroyed right now, whether the bile ducts are blocked and whether the liver is fulfilling its production tasks. Three layers, three different messages.

Cell damage (transaminases). ALT and AST are enzymes that sit inside liver cells. When cells are damaged, these enzymes leak into the bloodstream. The more cells are affected, the higher the values. ALT is liver-specific. AST is also found in muscle and heart tissue.

Bile obstruction (cholestasis). GGT, alkaline phosphatase (ALP) and bilirubin show whether the bile ducts are clear. A blockage can result from gallstones, medications or swelling of liver tissue. The typical pattern: GGT and ALP rise together.

Synthetic function. Albumin and INR show whether the liver still produces what it should. Albumin is made exclusively in the liver. When albumin drops below 3.5 g/dl, that points to chronic liver damage. INR measures clotting ability, which also depends on liver function.

A practical example: A doctor reports elevated liver values. A closer look shows ALT at 52 U/L, AST at 28 U/L, GGT at 35 U/L. Only ALT is elevated. That suggests mild liver cell damage, for example from excess weight or fatty liver. In Lab2go all three values can be viewed over time to see whether it is a one-time outlier or a trend.

The 6 Key Liver Markers

This table is a reference sheet. Ranges follow current European laboratory standards (2026).

For a broader view of all markers, the guide on understanding blood values is a useful companion.

AST vs. ALT: Why the Difference Matters

ALT is the liver-specific marker. The enzyme is found almost exclusively in liver cells. When ALT is elevated, the damage very likely sits in the liver. AST, on the other hand, also resides in heart and skeletal muscle, kidney and brain. An elevated AST value alone does not tell where the signal originates.

The De Ritis ratio makes the difference measurable. AST is divided by ALT:

• Ratio below 1: ALT is higher than AST. That points to acute liver cell damage, typical in fatty liver, acute viral hepatitis or medication-related injury.
• Ratio above 1: AST is higher than ALT. That suggests muscle damage, chronic alcohol injury or advanced liver disease (cirrhosis).

Practical scenario: A heavy CrossFit workout took place yesterday. Today the blood panel shows AST 78 U/L, ALT 32 U/L. De Ritis ratio: 2.4. That is not a liver problem. That is muscle soreness. This happens constantly in practice: athletes get worried because their doctor mentions elevated liver values. But only AST is elevated and ALT stays within range.

For this reason it is often advised to wait 48 to 72 hours after intense training before having blood drawn. It also helps to document the context in Lab2go: training yes or no, intensity, timing. This prevents misinterpretation at the next measurement.

GGT: The Alcohol Marker — and More

GGT (gamma-glutamyl transferase) is the most sensitive marker for alcohol consumption. Even moderate drinking over several days can raise GGT 2 to 5 times. The half-life is 14 to 26 days. After complete alcohol abstinence, GGT drops by half within 2 to 4 weeks. After 6 to 8 weeks of abstinence most people return to normal.

But GGT does not only respond to alcohol. Three other causes are at least as common:

Medications. Acetaminophen (paracetamol), statins, antiepileptics, antibiotics and hormonal contraceptives can elevate GGT in isolation. These substances induce liver enzymes that pull GGT up with them. If GGT is elevated and regular medication is taken, this connection belongs in the conversation with the doctor.

Excess weight. Obesity raises GGT independently of alcohol. The mechanism is non-alcoholic fatty liver disease (NAFLD), which affects roughly 30 percent of adults. GGT typically rises mildly to 60 to 120 U/L.

Metabolic syndrome. GGT correlates with insulin resistance, elevated triglycerides and high blood pressure. Studies show that GGT in the upper normal range (above 40 U/L in men) is an independent risk factor for type 2 diabetes and cardiovascular disease.

A practical example: GGT is 85 U/L. No alcohol is consumed. But a doctor-prescribed statin is taken regularly and the BMI is 29. Whether the medication and excess weight explain the value is a question for medical review. If CRP is elevated at the same time, there may be an inflammatory component.

Common Causes of Elevated Liver Values

Elevated liver values rarely have a single cause. In practice, six triggers account for over 90 percent of cases.

Alcohol. Regular consumption above the amounts considered low-risk directly damages liver cells. Typical pattern: GGT strongly elevated, AST moderately elevated, ALT mildly elevated, De Ritis ratio above 1.

Medications. Acetaminophen is the most common cause of acute liver failure in Western countries, but only with excessive intake. Statins, NSAIDs and antibiotics can mildly elevate liver values without true damage occurring.

Excess weight and fatty liver (NAFLD). 30 percent of adults in Western countries have fatty liver, most without knowing it. ALT is mildly elevated (40 to 80 U/L), GGT likewise. Ultrasound shows a dense liver structure.

Intense exercise. AST rises 2 to 5 times after hard training because the enzyme is also present in muscle tissue. ALT stays normal. This is physiological and not a cause for concern. A complete blood count taken after training delivers distorted liver values.

Viral hepatitis. Hepatitis B and C cause chronically elevated transaminases. ALT is often 3 to 10 times the upper limit. Screening for hepatitis antibodies is part of the basic workup for unexplained liver values.

Dietary supplements. Green tea extract with high EGCG content, niacin in high amounts and kava are on the list of hepatotoxic dietary supplements. Anyone taking dietary supplements should discuss liver value checks with their doctor. More on this in the supplements section below and in the supplement beginners guide.

Fatty Liver (NAFLD): The Silent Epidemic

Non-alcoholic fatty liver disease is the most common liver condition in the Western world. 30 percent of adults are affected. Among those with obesity, prevalence rises to 70 to 80 percent. The challenge: NAFLD causes no symptoms for a long time.

How does fatty liver develop? Excess calories, especially fructose and saturated fats, are stored as triglycerides in the liver. When more than 5 percent of liver cells accumulate fat, that is steatosis. Insulin resistance amplifies the process: the liver takes up more fatty acids than it can break down.

Typical lab picture: ALT mildly elevated (40 to 80 U/L), GGT mildly elevated (50 to 100 U/L), AST normal or mildly elevated, De Ritis ratio below 1. Triglycerides often above 150 mg/dl, HDL cholesterol low. Diagnosis is confirmed by ultrasound.

Stages of NAFLD:

1. Simple steatosis. Fat accumulation without inflammation. Potentially reversible.
2. Steatohepatitis (NASH). Fatty liver with inflammation. ALT rises further, CRP may be elevated. Still potentially reversible.
3. Fibrosis. Connective tissue remodeling begins. Albumin may drop. Partially reversible.
4. Cirrhosis. Scar tissue replaces functional liver tissue. Not reversible. End-stage liver disease.

Context: Stages 1 and 2 are considered responsive to lifestyle change. In studies, liver values normalized in many patients within 3 to 6 months after a weight reduction of 7 to 10 percent of body weight. Which measures make sense in an individual case is decided by the treating doctor.

For a view of the full profile including lipids and inflammatory markers, the biomarker baseline checklist offers an overview.

Supplements and Liver Values: Evidence and Risks

Some dietary supplements and medications can influence liver values. This section puts the evidence in context and is not a recommendation for use. Whether and in what form a product is taken should be clarified with a doctor, especially with abnormal liver values or existing conditions.

Substances with possible liver burden (case reports and studies):

• Niacin (vitamin B3) in high amounts: Slow-release preparations in particular have been linked to liver injury. Typically, ALT can rise 2 to 5 times.
• Green tea extract with high EGCG content: Case reports describe liver damage up to acute liver failure.
• Kava: Because of reports of liver injury, sale has been restricted or prohibited in several countries; the legal situation differs from country to country.
• Anabolic steroids and prohormones: 17-alpha-alkylated steroids are considered directly liver-toxic. ALT and AST regularly rise 5 to 20 times above normal.

Substances for which studies examine possible liver-related effects (evidence limited and inconsistent):

• Silymarin (milk thistle): Antioxidant properties are discussed. Studies in NAFLD examine effects on transaminases; results are not consistent.
• NAC (N-acetylcysteine): Precursor to glutathione, an important detoxification molecule of the liver. Used medically in hospitals for acetaminophen poisoning. For other situations the evidence is limited.
• Omega-3 fatty acids: Studies examine effects on liver fat and triglycerides in NAFLD; findings are not conclusive.

Anyone taking products or medications that may burden the liver should discuss monitoring intervals for liver values with their doctor. For background, see the supplement beginners guide.

When to See a Doctor

Not every elevated liver value requires immediate action. But four situations are a clear signal to see a physician.

ALT above 3 times the upper limit. That means above 135 U/L in men and above 102 U/L in women. This indicates relevant liver cell damage that needs investigation. Causes range from medications to viral hepatitis to autoimmune hepatitis.

Visibly elevated bilirubin (jaundice). When the skin or whites of the eyes turn yellow, bilirubin is above 2 to 3 mg/dl. This can indicate bile duct obstruction, hemolysis or severe liver damage. Immediate workup with ultrasound and extended lab panel.

Upper right abdominal pain. Pressure pain below the right rib cage combined with elevated liver values suggests liver enlargement, gallbladder inflammation or gallstones. Imaging is mandatory.

Unexplained weight loss. More than 5 percent weight loss in 3 months without dieting, combined with elevated liver values, needs investigation. Causes range from chronic hepatitis to liver tumors.

If it is unclear whether values are concerning, comparing them over time in Lab2go helps. A one-time outlier after exercise or alcohol is different from a rising trend across three measurements.

Tracking: How Often to Test

The testing frequency depends on the baseline situation.

Standard (healthy adults). Once a year as part of a routine blood panel. ALT, AST, GGT and bilirubin belong to the basic panel. Cost as an out-of-pocket test: 15 to 30 euros.

Products or medications with possible liver burden. Monitoring intervals are set by the doctor. An extended panel with albumin and ALP costs 40 to 70 euros.

Diagnosed fatty liver (NAFLD). Often quarterly checks until values normalize, then every 6 months. Tracking the trend alongside body weight and triglycerides makes medical interpretation easier.

After an acute elevation. A re-test after 4 to 6 weeks shows whether the cause has been addressed. It is useful to document context: medications, alcohol, training, newly taken products.

Context can be recorded with every measurement: training in the last 48 hours, alcohol intake, current medication, products taken. For a deeper methodology on biomarker tracking, see the guide on long-term biomarker tracking.

Liver Values in Context With Other Markers

Liver values never stand alone. Three connections to other biomarkers are especially important.

Liver values and inflammation. An inflamed liver (steatohepatitis) raises CRP. When ALT and GGT rise together with CRP, an inflammatory liver condition is likely. More on inflammatory markers in the guide on inflammation markers in blood.

Liver values and lipids. Fatty liver and disrupted lipid metabolism go hand in hand. Elevated triglycerides, low HDL and elevated ALT form a typical NAFLD pattern. The lipid profile provides important additional information about liver health.

Liver values and blood count. Bilirubin is directly linked to hemoglobin breakdown. Elevated bilirubin combined with low hemoglobin and high LDH points to hemolysis, which is not liver disease but accelerated breakdown of red blood cells. A complete blood count helps with differentiation.

Your Liver at a Glance: Orientation

Liver values are tools, not diagnoses. A single elevated ALT reading is no reason to panic. But a pattern of elevated transaminases, rising GGT and abnormal lipids tells a story that should be interpreted medically.

Three steps for orientation:

1. Record a baseline. At the next appointment, ALT, AST, GGT and bilirubin can be measured. Cost: 15 to 30 euros.
2. Document context. Alcohol, medications, products, training. Everything that can influence liver values.
3. Watch the trend. A single value is a point. Three measurements over 12 months form a trend.

The biomarker baseline checklist helps to document everything digitally. Check out the features of Lab2go or compare the plans and pricing.

This article is purely informational and does not replace medical advice. Intake, dose and therapy should be clarified with a doctor. If ALT exceeds 3 times the upper limit, or there is visible jaundice or upper abdominal pain, seek medical advice promptly. Self-tracking complements medicine. It does not replace it.