High liver enzymes (AST and ALT): what the number means and what tests to get

"High liver enzymes" is one of the lines that worries people most on a lab report, and it usually arrives without warning: you had a routine blood test and your ALT or AST came back flagged. The two enzymes go by several names. AST (aspartate aminotransferase) is also called SGOT, and Mexican reports print it as TGO; ALT (alanine aminotransferase) is also called SGPT, or TGP in Mexico. The old abbreviations come from serum glutamic oxaloacetic and glutamic pyruvic transaminase.^[4][5] A high result does not always mean a condition that needs care,^[4] and a mild abnormality is common: in a UK primary care study, 30% of liver test requests had at least one result out of range.^[2] Here is what these enzymes measure, what your number means according to the guidelines, what raises it, which tests are usually ordered with them and when not to wait.

First, what does not wait. If along with the result you have unexplained yellow skin or eyes, the British guideline calls for immediate assessment.^[2] If the yellow skin comes with confusion, unusual drowsiness, or bleeding and bruising that appear easily, the American guideline treats it as acute hepatitis requiring immediate referral to a liver specialist.^[1] In those cases, stop reading and get medical care today.

What AST and ALT are and what it means when they are high

ALT is an enzyme, a protein that speeds up chemical reactions in the body, and it is found mainly in the liver; normally there is little of it in the blood.^[4] AST is also found mainly in the liver, but also in the heart, muscles and other tissues.^[5] When one or both rise, it may point to some kind of liver damage,^[5] and that difference in origin gives a first clue: a high ALT points more strongly to the liver, while when AST rises on its own, muscle joins the list of explanations.^[1][5]

The liver enzymes are part of liver function tests, or a liver panel, which usually also include alkaline phosphatase, GGT, bilirubin, albumin, total protein, lactate dehydrogenase and sometimes prothrombin time.^[6] The British guideline defines a shorter standard panel: bilirubin, albumin, ALT, alkaline phosphatase and GGT, plus a complete blood count if there is none from the last 12 months.^[2] If they were ordered as part of a comprehensive metabolic panel, it is the same measurement.

A high number, on its own, does not tell you what is going on or how serious it is. MedlinePlus puts it this way: a high ALT result does not always mean you have a condition that requires medical care.^[4] What matters is how far it rises above the limit, whether it repeats, which other results come with it and what surrounds it: weight, alcohol, medications, exercise. The British guideline stresses a point that applies to everyone: an abnormal result should be interpreted after reviewing previous results.^[2]

What does an ALT of 45, 80 or 200 mean?

The American College of Gastroenterology (ACG) guideline makes two points that change how you read the report. First: the healthy range of ALT, in people without liver risk factors, is 29 to 33 U/L in men and 19 to 25 U/L in women, and values above it should be evaluated.^[1] Second: AST or ALT elevation is graded in multiples of the upper limit, from borderline to severe.^[1] The table applies those grades to a limit of 33 in men and 25 in women. Your lab sets its own limit and prints it next to the result; if it is different, the multiples change, as the note below explains, along with our piece on why the reference range is not your personal norm.

The same grading scale applies to AST.^[1] What the guideline does not offer is a separate healthy range for AST, so for AST the starting point is your lab's limit. And a detail that gets forgotten: the grades set how urgent the evaluation is, not the cause. An ALT of 80 can come from fatty liver, alcohol, a medication or a week of weightlifting; what tells them apart is the context and the tests that come with it.^[1][2]

What raises liver enzymes: the most common causes

The British guideline sums up the map: alcohol-related liver disease, non-alcoholic fatty liver disease and viral hepatitis are the three most common causes, and most adults with abnormal liver tests end up identified with one of the first two.^[2] Add to that medications, herbal products and supplements, and causes that do not come from the liver, such as muscle.^[1]

Fatty liver linked to metabolic factors

This is a buildup of fat in the liver that is not caused by heavy drinking. Today it is called MASLD, metabolic dysfunction-associated steatotic liver disease; it used to be called NAFLD, non-alcoholic fatty liver disease.^[7] The 2024 European guideline defines it as fat in the liver plus at least one cardiometabolic risk factor, and describes it as the most common chronic liver disease.^[3] About 24% of US adults are estimated to have it, it is most common among Hispanic people, and it occurs in one third to two thirds of people living with type 2 diabetes.^[7]

The factors that come with it are familiar: overweight or obesity, insulin resistance or type 2 diabetes, high triglycerides and metabolic syndrome, which includes a large waist.^[8] It is usually silent, with few or no symptoms; if there are any, tiredness or discomfort in the upper right abdomen.^[8] That is why a high ALT on a routine test is often the first clue, and why it is worth reading together with your triglycerides, your fasting glucose and, if you have it, your HOMA-IR.

Alcohol

Along with fatty liver, alcohol is one of the most common causes,^[2] and the amount matters. The ACG guideline considers women who drink more than 140 g of alcohol a week and men who drink more than 210 g at risk of alcohol-related liver disease when their AST is also higher than their ALT.^[1] The European guideline separates metabolic fatty liver from a mixed form, called MetALD, starting at more than 20 g a day in women and more than 30 g a day in men.^[3] The British one uses 14 units or fewer a week as the recommended limit.^[2] Grams mean little in daily life, so what helps at the appointment is writing down what you drink, what size and how many days a week.

Medications, herbal products and supplements

Some medications can raise ALT, including certain cholesterol and pain medicines, as can some toxic substances.^[4] The ACG guideline asks about everything a person takes, including dietary supplements and herbal products, because they are also among the causes of liver injury.^[1] The practical rule is the usual one: do not stop or change anything on your own; make a complete list with doses and start dates and bring it to the appointment.^[4]

Intense exercise and muscle

This is the cause that surprises people most. In a study of 15 healthy men, used to moderate activity but not to weightlifting, one hour of weightlifting raised AST and ALT significantly, and they stayed high for at least seven days afterward.^[9] Muscle enzymes such as CK rose even more.^[9] The authors conclude that intense muscular exercise should be considered a cause of high liver enzymes without symptoms.^[9]

MedlinePlus also lists intense exercise among the things that affect ALT, along with age, sex, weight, some medications and supplements and the phase of the menstrual cycle,^[4] and the ACG guideline includes strenuous exercise and muscle damage among the causes that do not come from the liver.^[1] If you trained hard in the week before the test, tell your doctor: a result taken after a few days of rest may tell a different story. There is more on the cycle in our piece on the menstrual cycle and lab results.

Viral hepatitis

Hepatitis B and C can go years without symptoms. WHO estimates that 47 million people live with chronic hepatitis C and that the infection often goes undiagnosed for decades.^[10] Testing is done in two steps: antibodies against the virus and, if positive, viral RNA to confirm chronic infection.^[10] For hepatitis B, the ACG guideline uses the surface antigen, HBsAg.^[1] That is why viral tests appear in the work-up of a high ALT in both guidelines.^[1][2]

The AST/ALT ratio

Comparing the two enzymes gives a clue, not a conclusion. When AST is higher than ALT in someone who drinks above the ACG thresholds, that guideline considers the person at risk of alcohol-related liver disease.^[1] The British guideline adds that an AST/ALT ratio above 1 may indicate advanced fibrosis, and that it remains useful even when both values are within the reference range.^[2] What does not help is doing the math at home and drawing conclusions: your doctor interprets the ratio together with the rest of the report.

Normal liver enzymes do not always mean a healthy liver

The opposite also happens. The British guideline warns that AST and ALT can be normal even with cirrhosis, and that normal liver tests do not rule out advanced fibrosis.^[2] The European guideline recommends looking for liver disease with fibrosis in people with type 2 diabetes, with abdominal obesity and at least one more metabolic risk factor, or with abnormal liver tests, and advises against general screening of the whole population.^[3] To estimate fibrosis, both guidelines prefer blood-based scores such as FIB-4 over reading liver enzymes alone.^[2][3]

In the European guideline, FIB-4 has two cutoffs, 1.3 and 2.67, valid up to age 65; above that age the lower cutoff becomes 2.0.^[3] Your doctor calculates and reads it. Your part is knowing whether you have any of those risk factors, because that changes what is worth ordering even if your ALT came back in range.^[3]

What to order along with AST and ALT

A high ALT is almost never evaluated alone. This table gathers what the guidelines and MedlinePlus place around it; what gets ordered and in what sequence is your doctor's call, based on the grade and your context.^[1][2][6]

If your doctor suspects a muscle origin, they may consider CK, the muscle enzyme that in the weightlifting study rose much more than the liver enzymes.^[9] And if ferritin appears on your report for another reason, our piece on low ferritin explains what it measures.

Repeat or complete: what to do with the result and when to test again

Here the two major guidelines put the emphasis in different places, and it helps to know both. The ACG guideline asks to repeat the panel or do a clarifying test before starting to look for causes, to confirm the result is truly abnormal.^[1] The British one warns against simply repeating the same panel: it is only justified when the value is expected to normalize after an identified acute cause, and otherwise it proposes completing the work-up with cause tests.^[2] In practice they agree on what matters: a high result is not left without a next step.

MedlinePlus adds that a recent illness can make some results abnormal temporarily, which is why your doctor may repeat the tests.^[6] For a repeat test to be useful, take it under comparable conditions:

• Fasting as instructed: for a liver panel, 10 to 12 hours is usually requested.^[6] Our piece on fasting before a blood test covers water, coffee and medications.
• No weights or unusual training in the days before: in the study cited, the effect lasted at least a week.^[9]
• Away from a recent acute illness, unless your doctor says otherwise.^[6]
• The same list of medications and supplements, with no changes on your own.^[4]
• The same lab, if possible, so the upper limit is the same and the comparison with the previous result makes sense.^[2]

How long to wait is your doctor's decision, based on the grade. For mild elevations, the ACG guideline proposes a medical history, reviewing alcohol and medications, hepatitis and iron tests, and an ultrasound if there is excess weight or features of metabolic syndrome.^[1] For moderate elevations it adds testing for acute hepatitis.^[1] If your last test was more than a year ago, your annual preventive check-up is a good time to include it.

Meanwhile, what adds most to the conversation is what you measure at home. The European guideline recommends physical activity for people with fatty liver, preferably more than 150 minutes a week of moderate intensity or 75 of vigorous intensity, tailored to each person, and discourages alcohol.^[3] Weight and waist with dates, steps and sleep from your watch, and an honest alcohol log are the part only you can contribute; if your weight is not moving as you expect, this piece covers what to measure.

Warning signs

A mild elevation without symptoms is worked up calmly. What changes the pace are symptoms of liver damage and very high values. MedlinePlus lists as symptoms of liver damage nausea and vomiting, loss of appetite, tiredness, weakness, yellow skin and eyes, swelling or pain in the abdomen, swelling in the ankles and legs, dark urine or pale stools, and frequent itching.^[4]

• Unexplained yellow skin or eyes (jaundice): the British guideline calls for immediate referral.^[2]
• Yellow skin with confusion, unusual drowsiness, or easy bleeding and bruising: in acute hepatitis with impaired clotting or mental status, the ACG guideline calls for immediate referral to a liver specialist, and acute liver failure is evaluated immediately whatever the ALT.^[1] This is care today, through the emergency room if needed.
• AST or ALT above 15 times the limit: a severe elevation according to the ACG guideline, which then looks for drug-related injury and reduced blood flow to the liver.^[1] Do not wait for the next check-up.
• 5 to 15 times the limit: the guideline adds testing for acute hepatitis A, B and C.^[1] See a doctor within days, not months.
• Dark urine, pale stools, abdominal pain or swelling, or vomiting that will not stop, at any value: see a doctor soon.^[4]

What to bring to the doctor

An appointment about high liver enzymes moves much faster when you arrive with the full series and the context, because the British guideline asks for each result to be read in light of the previous ones.^[2]

1. All your AST and ALT results with dates, from oldest to newest, with the limit each lab used.^[2]
2. The rest of the liver panel: alkaline phosphatase, GGT, bilirubin, albumin and your latest complete blood count.^[2][6] If you want to review it first, here is the complete blood count line by line.
3. List of medications, herbal products and supplements, with doses and start dates.^[1]
4. A two-week alcohol log: what, what size and how many days.^[1][3]
5. Exercise in the week before the test, especially weights or unusual efforts.^[9]
6. Weight, waist, glucose, triglycerides and HDL with dates; if you have your triglyceride/HDL ratio or your A1C, bring those too.^[8]
7. Symptoms with start dates, if any: tiredness, discomfort on the right side, itching, changes in urine or stool color.^[4]
8. History that matters for hepatitis: transfusions, procedures with equipment that may not have been properly sterilized, shared injection equipment, and whether you have ever been tested for hepatitis B or C.^[10]