AST/ALT Ratio Explained
The relationship between two liver enzymes tells your GP whether a result fits fatty liver, alcohol, cirrhosis, or a muscle problem that has nothing to do with your liver.
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The Quick Answer
AST (aspartate aminotransferase) and ALT (alanine aminotransferase) are both liver enzymes, and both are reported on almost every standard liver function test. The AST/ALT ratio, also called the De Ritis ratio, is simply AST divided by ALT. That one number narrows down what is driving an abnormal liver panel, which is why GPs look at it before ordering further tests.
Why the ratio works: ALT is found almost exclusively in the liver, while AST is also found in muscle, heart tissue and red blood cells. So when both enzymes are raised, which one is raised more tells you something about the mechanism of injury. A ratio under 1 (ALT higher than AST) points toward fatty liver disease. A ratio above 2, with a raised GGT, points toward alcohol. A rising ratio in someone with known liver disease can signal advancing fibrosis. A very high AST with a normal ALT points away from the liver entirely, toward muscle.
Typical Australian adult upper reference limits sit around 30 to 40 U/L for ALT and around 30 to 40 U/L for AST, with most laboratories quoting a slightly lower limit for women than for men. Assay methods and cutoffs differ between laboratories, so the interval printed on your own report always takes precedence.
Where ALT and AST Come From
Understanding why the ratio works at all starts with understanding that these two enzymes are not interchangeable measures of the same thing.
ALT (Alanine Aminotransferase)
Primary tissue: Liver (mostly cytoplasm of liver cells)
Plasma half-life: Approximately 47 hours
ALT is found in meaningful quantity almost exclusively in the liver, which is what makes it the more liver-specific of the two enzymes. A rise in ALT with a normal AST points strongly toward the liver as the source. Its longer half-life also means ALT stays elevated for longer after a single liver insult.
AST (Aspartate Aminotransferase)
Primary tissue: Liver, skeletal muscle, heart muscle, kidneys, red blood cells, brain
Plasma half-life: Approximately 17 hours
AST is present in many tissues besides the liver, so an isolated rise in AST is genuinely ambiguous until you know whether ALT, CK and the blood film are normal. AST also exists in two forms, a cytoplasmic form and a mitochondrial form, and the mitochondrial form is released preferentially in alcohol-related and severe hepatocyte injury.
Interpreting the AST/ALT Ratio
The ratio is most useful once at least one of the two enzymes is genuinely outside its reference interval. Read alongside GGT and the overall clinical picture, these patterns cover the great majority of cases seen in Australian general practice.
Ratio below 1, both AST and ALT mildly raised
The classic metabolic dysfunction associated fatty liver disease (MAFLD) picture
Common causes: Fatty liver disease from excess weight, insulin resistance or type 2 diabetes (most likely). Early or mild chronic hepatitis of any cause, where ALT typically still runs ahead of AST.
Ratio between 1 and 2
A non-specific, intermediate pattern
Common causes: More established chronic liver disease of almost any cause, including viral hepatitis B or C, autoimmune hepatitis, drug-induced liver injury, or fatty liver disease that is starting to scar. On its own this range does not point to one diagnosis.
Ratio above 2, with a raised GGT
The classic alcohol-related liver disease pattern
Common causes: Regular or heavy alcohol intake (most likely). Acute alcoholic hepatitis. The GGT rising alongside supports an alcohol source rather than a coincidental muscle cause of the high AST.
Ratio above 1, in someone with known or suspected cirrhosis
A marker that fibrosis has become advanced, regardless of the original cause
Common causes: Cirrhosis from any cause: long-standing fatty liver disease, chronic viral hepatitis, autoimmune liver disease, or alcohol. The ratio tends to climb as scarring advances, and a ratio above 1 in cirrhosis carries a different meaning to a ratio above 1 in an otherwise healthy liver.
AST very high, ALT normal or near-normal
Points away from the liver toward muscle
Common causes: Rhabdomyolysis, hard or unaccustomed training, statin-related muscle injury, a myopathy from an untreated underactive thyroid, or a haemolysed blood sample. Should prompt a creatine kinase (CK) test before assuming a liver cause.
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Causes of an Abnormal Ratio, in Detail
Ordered roughly by frequency in Australian general practice.
Metabolic dysfunction associated fatty liver disease (MAFLD)
Fat accumulation and low-grade inflammation inside liver cells damages the cell membrane, releasing the cytoplasmic enzymes, ALT slightly more than AST
The single most common cause of a low AST/ALT ratio with mild enzyme elevation in Australian general practice, closely tied to excess weight, insulin resistance and type 2 diabetes. Confirmed by liver ultrasound rather than by blood tests alone. Weight loss of 5 to 10 percent of body weight often improves both the enzymes and the ratio.
Alcohol-related liver disease
Chronic alcohol exposure preferentially damages mitochondria inside liver cells, releasing the mitochondrial fraction of AST, and also depletes vitamin B6, which blunts ALT production
The classic driver of a ratio above 2. GGT is usually the first enzyme to rise with regular drinking and the most sensitive marker of ongoing intake, though it is not specific on its own. Abstinence for 4 to 6 weeks often produces a clear fall in all three enzymes, which is itself a useful diagnostic and monitoring tool.
Cirrhosis of any cause
Reduced hepatic blood flow and clearance slow AST removal more than ALT, and vitamin B6 deficiency further lowers measured ALT activity
A rising ratio over serial tests in someone with chronic liver disease is a recognised, if imperfect, signal that fibrosis is advancing toward cirrhosis. Absolute enzyme levels can actually fall as cirrhosis progresses, because there are fewer functioning liver cells left to leak enzymes, which is why the ratio matters more than the raw numbers at this stage.
Acute viral hepatitis (A, B, C, E)
Direct viral injury to liver cells causes marked, usually ALT-predominant, enzyme release in the acute phase
Typically produces a ratio below 1, sometimes with ALT and AST both in the hundreds or thousands of U/L. As acute hepatitis evolves toward chronic infection or resolves, the ratio and absolute levels change accordingly. Viral serology confirms the diagnosis.
Drug-induced liver injury
Direct hepatocellular toxicity, an idiosyncratic immune reaction, or in some cases a cholestatic mechanism, depending on the drug
Paracetamol overdose classically causes a very high AST and ALT with a ratio that can exceed 1 due to the severity of hepatocyte necrosis. Many other medications, herbal supplements and some over-the-counter products can produce a wide range of patterns. A careful medication and supplement history is essential whenever the cause is not obvious.
When AST Is High but ALT Is Normal: Check Muscle Before Liver
A markedly raised AST alongside a normal or near-normal ALT is one of the more commonly misread patterns on a blood test. Because AST is not liver-specific, this combination should prompt a creatine kinase (CK) test before liver disease is assumed.
Rhabdomyolysis
Severe muscle breakdown, from extreme exertion, a crush injury, prolonged immobility, seizures, or certain drugs, releases very large amounts of AST and CK into the bloodstream. CK is typically raised far more dramatically than AST, often into the tens of thousands of U/L, and urine may appear dark from myoglobin. This is a medical emergency because myoglobin can cause acute kidney injury, and needs urgent assessment, intravenous fluids and monitoring of kidney function.
Hard or unaccustomed exercise
A new resistance training program, a marathon, downhill running, or a CrossFit-style session that involves a lot of eccentric muscle loading can raise AST (and to a lesser extent ALT) for several days afterward. CK rises alongside it and usually confirms the muscle source. Levels typically normalise within 5 to 7 days of rest, and repeating the blood test after a short break resolves any doubt.
Statin-associated muscle symptoms
Statins occasionally cause a mild to moderate myopathy, with muscle aches and a raised CK and AST, most often at higher doses or when combined with interacting drugs such as clarithromycin, some antifungals, or fibrates. Your GP may pause the statin temporarily to see whether CK and AST fall, then consider a lower dose, a different statin, or an alternative lipid-lowering agent.
Untreated hypothyroidism, and (separately) coeliac disease
An untreated underactive thyroid can cause a mild myopathy with a raised CK and a modest, AST-predominant rise in transaminases, which settles once thyroid hormone replacement is established. Coeliac disease also causes unexplained, usually mild, enzyme elevation in a meaningful minority of newly diagnosed patients, though that pattern is more often ALT-predominant than AST-predominant, and it typically normalises on a strict gluten-free diet. Thyroid function tests and coeliac serology (anti-tTG IgA with total IgA) are both reasonable, inexpensive additions when an unexplained enzyme pattern has no obvious cause.
Laboratory artefacts that can also distort the ratio
Haemolysed blood sample
Red blood cells contain a substantial amount of AST (and LDH), so if cells rupture in the collection tube, during transport, or on the centrifuge, before the plasma is separated, AST leaks out and falsely raises the result, sometimes markedly, while ALT is unaffected. A haemolysed sample is usually flagged by the laboratory and the correct response is simply to repeat the blood draw rather than to investigate a false AST/ALT ratio.
Macro-AST
A rare, benign phenomenon in which AST binds to an immunoglobulin, forming a large complex that the body clears from the bloodstream far more slowly than normal AST. This produces a persistently raised AST, sometimes for years, with an entirely normal ALT, GGT, ALP and bilirubin, and no evidence of liver, muscle or blood cell disease on any other test. It is analogous to macro-CK and macro-amylase, and is confirmed with a specific laboratory technique (polyethylene glycol precipitation) once the more common causes have been excluded.
Using AST to Estimate Fibrosis: FIB-4 and APRI
Beyond the simple ratio, AST also feeds into two widely used, free calculations that estimate the likelihood of significant liver scarring without needing a biopsy.
FIB-4
FIB-4 = (Age in years x AST) / (Platelets [10^9/L] x square root of ALT)
Below 1.3: advanced fibrosis unlikely (below 2.0 if you are over 65). 1.3 to 2.67: indeterminate. Above 2.67: high probability of advanced fibrosis, refer for specialist assessment.
The most widely used non-invasive fibrosis score in Australian and international guidelines because it needs only an age and three routine blood results, no special equipment. It was validated primarily in hepatitis C and MAFLD populations, so it is best used as a screening step that decides who needs a FibroScan or hepatology referral, not as a final diagnosis.
APRI (AST to Platelet Ratio Index)
APRI = ((AST / upper limit of normal for AST) / Platelets [10^9/L]) x 100
Below 0.5: significant fibrosis unlikely. 0.5 to 1.5: indeterminate. Above 1.5: suggests significant fibrosis, and above 2 raises concern for cirrhosis.
Older and simpler than FIB-4, originally developed and validated in chronic hepatitis C, and generally considered somewhat less accurate than FIB-4 in fatty liver disease, but still used as a quick first-pass check, particularly where a platelet count and AST are the only tests immediately available.
What Your GP Will Do Next
Repeat the full liver panel after a few weeks
A single abnormal result is often repeated after 2 to 4 weeks to see whether it was transient, for example after a hard training session or a big weekend, or whether the pattern persists. The repeat includes ALT, AST, GGT, ALP, bilirubin and albumin, not AST and ALT in isolation.
Take a careful alcohol and medication history
Your GP will ask directly about typical weekly alcohol intake, recent changes in drinking, all prescription and over-the-counter medications, and any supplements or herbal products, several of which are recognised, if under-reported, causes of abnormal liver enzymes.
Check creatine kinase (CK) if AST is disproportionately high
When AST is markedly raised relative to ALT, CK is the key next test. A raised CK confirms a muscle source and generally stops the liver work-up in its tracks. A normal CK redirects attention back to the liver or to a possible laboratory artefact.
Order a liver ultrasound
Ultrasound is usually the first imaging test, looking for fatty change, gallstones, bile duct dilation, and the size and texture of the liver. It is inexpensive, has no radiation, and is often enough to confirm fatty liver disease as the explanation for a ratio below 1 with mild enzyme elevation.
Consider a FibroScan (transient elastography)
If FIB-4 or APRI come back indeterminate or high, a FibroScan measures liver stiffness directly and non-invasively, giving a much more precise estimate of fibrosis stage than blood-based scores alone, and often avoids the need for a liver biopsy.
Test for viral hepatitis, iron overload, autoimmune disease and coeliac disease
When the cause is not obvious from history and imaging, hepatitis B and C serology, iron studies, autoimmune markers (ANA, smooth muscle antibody, immunoglobulins), thyroid function and coeliac serology (anti-tTG IgA with total IgA) round out the standard next-round work-up, particularly when the pattern is unexplained or AST-predominant.
Refer to a hepatologist or gastroenterologist when indicated
Referral is appropriate for a persistently high FIB-4 or APRI, an AST/ALT ratio that keeps rising over serial tests, evidence of cirrhosis on imaging, or any diagnostic uncertainty after the initial work-up.
When to Seek Urgent Care
Yellowing of the skin or eyes (jaundice)
Combined with a high AST/ALT ratio and other abnormal liver tests, jaundice suggests significant liver dysfunction and needs same-day medical assessment.
Confusion, drowsiness or a change in personality
These can be signs of hepatic encephalopathy in advanced liver disease and are a medical emergency requiring immediate hospital assessment.
Very dark, brown or cola-coloured urine with muscle pain or weakness
This combination, especially after intense exercise, a crush injury or a long period on the floor after a fall, raises concern for rhabdomyolysis and possible acute kidney injury, and warrants urgent same-day assessment or an emergency department.
Vomiting blood or passing black, tarry stools
These can indicate bleeding from oesophageal varices in advanced liver disease with portal hypertension, and require emergency department assessment.
Sudden abdominal swelling
New or rapidly worsening abdominal distension can reflect ascites (fluid accumulation) in decompensated liver disease and should be assessed promptly by your GP or an emergency department.
Sources and reference ranges
Adult reference ranges on this page follow the AACB and RCPA harmonised reference intervals unless stated otherwise; the range printed on your own report always takes precedence because laboratories differ.
- healthdirect Australia: liver function tests
- Pathology Tests Explained (Australasian Association for Clinical Biochemistry and Laboratory Medicine)
- Australasian Association for Clinical Biochemistry and Laboratory Medicine, publisher of the harmonised reference intervals
- healthdirect Australia: full blood count
AST/ALT Ratio (De Ritis Ratio): Frequently Asked Questions
What is a normal AST/ALT ratio?
The AST/ALT ratio, also called the De Ritis ratio, is simply your AST result divided by your ALT result. In adults without liver or muscle injury, serum ALT usually sits slightly higher than AST, which gives a ratio below 1. A ratio in the 0.7 to 1.0 range is generally considered unremarkable in someone with no other liver test abnormalities. The ratio only becomes clinically useful once at least one of AST or ALT is outside its own reference interval, because the ratio of two normal numbers still carries a wide range of possible values.
What does an AST/ALT ratio below 1 mean?
A ratio below 1, with both AST and ALT mildly raised, is the classic pattern of metabolic dysfunction associated fatty liver disease (MAFLD, previously called NAFLD), by far the most common cause of mildly abnormal liver enzymes in Australian adults. ALT tends to rise slightly more than AST because the fat accumulation and low-grade inflammation in fatty liver disease injures the cytoplasm of liver cells, where ALT is concentrated. This pattern is often accompanied by excess weight or waist circumference, insulin resistance, or an abnormal lipid panel, and is confirmed on liver ultrasound showing fatty change rather than by the ratio alone.
What does an AST/ALT ratio above 2 mean?
An AST/ALT ratio above 2, especially when the GGT is also raised, is the classic pattern of alcohol-related liver disease. Chronic alcohol use damages mitochondria inside liver cells, and AST is partly produced inside mitochondria while ALT is not, so AST rises disproportionately. This combination, sometimes summarised as the ratio being greater than 2 with a high GGT, has reasonable specificity for heavy alcohol intake, though it is not proof on its own. Your GP will ask about alcohol history directly and may repeat the tests after a period of abstinence to see whether the enzymes fall.
Can the AST/ALT ratio diagnose alcoholic liver disease by itself?
No single blood ratio can diagnose alcoholic liver disease on its own. The AST/ALT ratio above 2 with a raised GGT is a useful supporting pattern, but it can also occur in advanced cirrhosis from any cause, in some cases of acute alcoholic hepatitis where absolute enzyme levels are only mildly raised, and occasionally in non-alcoholic conditions. Diagnosis relies on the whole clinical picture: a careful alcohol history, examination findings, the pattern of other liver tests, and often imaging or a liver biopsy in ambiguous cases. Your GP uses the ratio as one clue among several, not as a stand-alone test.
Why does the AST/ALT ratio rise in cirrhosis even without alcohol?
As liver fibrosis advances toward cirrhosis, from any underlying cause, including viral hepatitis, autoimmune disease or long-standing fatty liver disease, the AST/ALT ratio tends to climb above 1 and eventually above 2. Two things drive this: measured ALT activity depends on vitamin B6 (as pyridoxal phosphate) as a cofactor, and B6 levels commonly fall in cirrhosis, blunting ALT more than AST. At the same time, reduced liver blood flow and impaired clearance in a scarred liver slow the removal of AST from the bloodstream more than ALT. So a rising ratio over time in someone with known liver disease is a recognised, if imperfect, marker that fibrosis may be progressing.
What does it mean if my AST is high but my ALT is normal?
A markedly raised AST with a normal or only mildly raised ALT points away from the liver and toward another tissue that also contains AST, most often skeletal muscle, heart muscle or red blood cells. Common causes include recent intense or unaccustomed exercise, rhabdomyolysis, statin-related muscle injury, and, less commonly, a myopathy from another cause such as an untreated underactive thyroid. Your GP will usually order a creatine kinase (CK) test next: a high CK alongside the high AST confirms a muscle source and takes the focus away from the liver. A normal CK instead points back toward liver causes or a laboratory artefact such as a haemolysed sample.
What is FIB-4 and how is it calculated from AST?
FIB-4 is a simple, free calculation that estimates the likelihood of advanced liver fibrosis using age, AST, ALT and your platelet count: FIB-4 equals age in years multiplied by AST, divided by platelets multiplied by the square root of ALT. A result below 1.3 (below 2.0 if you are over 65) makes advanced fibrosis unlikely, a result above 2.67 raises real concern and usually prompts referral, and a result in between is indeterminate and often followed up with an ultrasound-based elastography scan such as FibroScan. FIB-4 was developed and validated mainly in viral hepatitis and MAFLD, and is a screening tool, not a diagnosis.
Can exercise or hard training change my AST/ALT ratio?
Yes. Intense or unaccustomed exercise, particularly eccentric loading such as heavy squats, downhill running or a new resistance training program, can release AST from damaged muscle fibres within 24 to 48 hours, temporarily raising AST more than ALT and pushing the ratio upward. This is a normal physiological response, not liver disease, and it typically settles within 5 to 7 days as muscle repairs. Creatine kinase is usually raised at the same time, which is the clue that points to muscle rather than liver. If you have had a blood test shortly after a hard training session, mentioning this to your GP avoids unnecessary liver investigations.
Should I be worried about a mildly abnormal AST/ALT ratio?
A mildly abnormal ratio on its own, with AST and ALT only slightly outside their reference intervals, is common and usually reflects fatty liver disease, recent alcohol intake, medication effects or recent exercise rather than serious disease. It is worth taking seriously in the sense of repeating the test, reviewing alcohol intake and medications, and discussing it with your GP, but it is rarely an emergency. The pattern becomes more concerning when the ratio is combined with genuinely elevated absolute enzyme levels, an abnormal GGT or bilirubin, a low platelet count, or symptoms such as jaundice, abdominal swelling or unexplained weight loss, all of which warrant more urgent review.
Related Reading
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This page provides general educational information about the AST/ALT ratio and its use in assessing liver enzyme patterns. It is not a substitute for professional medical advice, diagnosis, or treatment. Always discuss abnormal blood test results with your GP, who has access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care.