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 does not replace medical advice. If your liver values are significantly elevated or you have symptoms, consult a doctor.

What Liver Values Actually Show

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: Your doctor reports elevated liver values. You look closer and see 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 you can see all three values over time and spot whether it is a one-time outlier or a trend.

The 6 Key Liver Markers

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

Marker	Legacy Name	Reference Range	What It Shows
ALT (GPT)	SGPT	below 45 U/L men, below 34 U/L women	Liver cell damage, liver-specific
AST (GOT)	SGOT	below 35 U/L	Liver cell damage + muscle damage, not liver-specific
GGT (Gamma-GT)	y-GT	below 60 U/L men, below 40 U/L women	Bile obstruction, alcohol, medications
Alkaline Phosphatase (ALP)	—	40 to 130 U/L	Bile obstruction, bone
Bilirubin (total)	—	below 1.2 mg/dl	Hemoglobin breakdown product, jaundice
Albumin	—	3.5 to 5.0 g/dl	Liver synthetic function

For a broader view of all markers, read the guide on understanding blood values.

AST vs. ALT: Why the Difference Matters

ALT is your 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 you where the signal originates.

The De Ritis ratio makes the difference measurable. Divide AST 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: You did a heavy CrossFit workout yesterday. Today your blood panel shows AST 78 U/L, ALT 32 U/L. De Ritis ratio: 2.4. That is not a liver problem. That is your 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.

Wait 48 to 72 hours after intense training before having blood drawn. Document the context in Lab2go: training yes or no, intensity, timing. This prevents misinterpretation at your 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 your GGT is elevated and you take regular medication, ask your doctor about this connection.

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: Your GGT is 85 U/L. You do not drink alcohol. But you take a daily statin and your BMI is 29. Before you worry, discuss with your doctor whether the medication and excess weight explain the value. If your 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 20 g/day in women and 40 g/day in men 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 at overdoses above 4 g/day. 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 always 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.

Supplements. Green tea extract with high EGCG content, high-dose niacin and kava are on the list of hepatotoxic dietary supplements. If you take a supplement stack, check liver values regularly. 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. Fully reversible.
2. Steatohepatitis (NASH). Fatty liver with inflammation. ALT rises further, CRP may be elevated. Still reversible.
3. Fibrosis. Connective tissue remodeling begins. Albumin may drop. Partially reversible.
4. Cirrhosis. Scar tissue replaces functional liver tissue. Irreversible. End-stage liver disease.

The good news: Stages 1 and 2 are fully reversible through lifestyle change. A weight reduction of 7 to 10 percent of body weight normalizes liver values in the majority of patients within 3 to 6 months. No medication needed. Calorie reduction and 150 minutes of exercise per week are enough.

If you want to check your full profile including lipids and inflammatory markers, start with the biomarker baseline checklist.

Supplements and Liver Values

As a biohacker or supplement user, you should keep a close eye on your liver values. Some popular supplements can stress the liver, while others protect it with solid evidence.

Supplements with liver burden:

• High-dose niacin (vitamin B3) above 500 mg/day: The slow-release form is especially hepatotoxic. ALT typically rises 2 to 5 times. Choose the flush form (nicotinic acid) at a lower dose or nicotinamide.
• Green tea extract (EGCG above 800 mg/day): Case reports show liver damage up to acute liver failure. Taking it on an empty stomach increases the risk. Keep EGCG below 400 mg/day and always take it with a meal.
• Kava: Banned in the EU due to hepatotoxicity. Still available in the US.
• Anabolic steroids and prohormones: 17-alpha-alkylated steroids are directly liver-toxic. ALT and AST regularly rise 5 to 20 times above normal.

Supplements with liver protection:

• Silymarin (milk thistle, 200 to 400 mg/day): Antioxidant, stabilizes liver cell membranes. Studies show a reduction of transaminases by 20 to 30 percent in NAFLD.
• NAC (N-acetylcysteine, 600 to 1200 mg/day): Precursor to glutathione, the liver’s most important detoxification molecule. Standard treatment for acetaminophen poisoning. Also useful as prevention when running a supplement stack with liver burden.
• Omega-3 fatty acids (2 to 4 g EPA/DHA): Reduce liver fat and triglycerides in NAFLD.

If your supplement stack includes niacin, green tea extract or other potentially hepatotoxic substances, test your liver values every 6 months. For supplement basics, read 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 you are unsure whether your values are concerning, compare them over time in Lab2go. A one-time outlier after exercise or alcohol is different from a rising trend across three measurements.

Tracking: How Often to Test

The right testing frequency depends on your 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.

Supplement stack with liver burden. Test every 6 months if you take high-dose niacin, green tea extract, anabolic compounds or other potentially hepatotoxic substances. An extended panel with albumin and ALP costs 40 to 70 euros.

Diagnosed fatty liver (NAFLD). Quarterly checks until values normalize. Then every 6 months. Track the trend alongside body weight and triglycerides.

After an acute elevation. Re-test after 4 to 6 weeks to verify the cause has been addressed. Document context: medications, alcohol, training, new supplements.

Record context with every measurement: training in the last 48 hours, alcohol intake, current medication, supplement stack. For a deeper methodology on biomarker tracking, read 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. Your 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: Next Steps

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 you should understand.

Three steps to get started:

1. Set your baseline. At your next appointment, get ALT, AST, GGT and bilirubin tested. Cost: 15 to 30 euros.
2. Document context. Alcohol, medications, supplements, training. Everything that influences liver values.
3. Watch the trend. A single value is a point. Three measurements over 12 months form a trend.

Start today with the biomarker baseline checklist and document everything digitally. Check out the features of Lab2go or compare the plans and pricing.

This article does not replace medical advice. If your ALT exceeds 3 times the upper limit, you have visible jaundice or upper abdominal pain, consult a doctor immediately. Self-tracking complements medicine. It does not replace it.