By You’ve had bloodwork done and the report comes back labelled “liver function tests” or “liver panel.” There are six, seven, sometimes eight numbers on it – ALT, AST, ALP, GGT, bilirubin, albumin, total protein, and possibly prothrombin time. Some are flagged. Some aren’t. Your doctor may have said everything looks fine, or may have mentioned following up on something, and you’re left trying to understand what any of it means.
Here’s the full picture – what each marker measures, what the normal ranges look like, what causes abnormalities, and how the pattern across multiple markers tells a clearer story than any single number alone.
The Misnomer Worth Knowing
“Liver function tests” is actually a misleading name for most of what’s measured. The majority of markers in a standard LFT panel – ALT, AST, ALP, GGT, and bilirubin – don’t directly measure liver function at all. They measure liver cell damage or bile flow disruption.
True liver function markers – the tests that actually assess what the liver is doing – are albumin, total protein, and prothrombin time (PT/INR). These reflect the liver’s ability to synthesize proteins and maintain metabolic processes.
This distinction matters because a patient can have severely impaired liver function with relatively modest enzyme elevations (as happens in end-stage cirrhosis, when few cells remain to leak enzymes), and conversely can have dramatically elevated enzymes with intact liver function (as in mild acute hepatitis that resolves completely).
The practical rule: ALT, AST, ALP, and GGT tell you that something is injuring liver cells or disrupting bile flow. Albumin and PT/INR tell you how well the remaining liver is actually working.
ALT – Alanine Aminotransferase
Normal range: approximately 7 – 56 U/L (men); 7 – 45 U/L (women)
ALT is an enzyme found almost exclusively in liver cells (hepatocytes). It lives in the cytoplasm of the cell and participates in amino acid metabolism. Because it’s so concentrated in the liver, elevated ALT is highly specific for liver cell injury – when liver cells are damaged or dying, ALT leaks out into the bloodstream.
ALT is the primary marker for hepatocellular (liver cell) damage. It’s the first marker most clinicians look at when assessing whether the liver itself – as opposed to the bile ducts – is the source of a problem.
Common causes of elevated ALT:
- Non-alcoholic fatty liver disease (NAFLD) – by far the most common cause of mildly elevated ALT in the US. An estimated 25-30% of American adults have NAFLD, many with mild ALT elevations they don’t know about.
- Viral hepatitis (A, B, C, D, E)
- Alcoholic liver disease
- Drug-induced liver injury – NSAIDs, acetaminophen, statins, certain antibiotics, herbal supplements
- Autoimmune hepatitis
- Celiac disease – an underrecognized cause of mild ALT elevation that resolves with a gluten-free diet
- Thyroid disease
- Intense exercise (though less so than AST, since ALT is less abundant in muscle)
AST – Aspartate Aminotransferase
Normal range: approximately 10 – 40 U/L (men); 10 – 34 U/L (women)
AST is found in the liver but also in significant quantities in skeletal muscle, heart muscle, red blood cells, and kidneys. This makes it less liver-specific than ALT – an elevated AST alone doesn’t always point to liver disease.
Within liver cells, AST is present in both the cytoplasm and the mitochondria. Mitochondrial AST is released when liver cells suffer deeper, more severe injury – particularly the type caused by alcohol. This is the foundation of the clinically important AST/ALT ratio, which the site has covered in depth in a dedicated article.
Key patterns:
- AST/ALT ratio below 1 (ALT dominant): typical of NAFLD, viral hepatitis, most drug-induced liver injury
- AST/ALT ratio above 2 (AST more than double ALT): strongly associated with alcohol-related liver disease; also seen in advanced cirrhosis from any cause
- Isolated high AST with normal ALT: consider muscle damage (intense exercise, rhabdomyolysis, inflammatory muscle disease), cardiac injury, or hemolysis
ALP – Alkaline Phosphatase
Normal range: approximately 44 – 147 U/L (adults; varies significantly by age and sex)
ALP is found on the canalicular membrane of hepatocytes – the surface facing the bile ducts – and in bone, intestine, placenta, and kidneys. It rises when bile flow is impaired (cholestasis) because bile duct pressure increases ALP production and release.
This makes ALP the primary marker for biliary or cholestatic disease, rather than hepatocellular injury.
When ALP is elevated disproportionately to ALT/AST:
- Bile duct obstruction (gallstones, pancreatic cancer compressing the duct, strictures)
- Primary biliary cholangitis (PBC) – autoimmune destruction of small bile ducts
- Primary sclerosing cholangitis (PSC) – inflammatory bile duct disease, strongly linked to IBD
- Drug-induced cholestasis
- Liver infiltration (lymphoma, sarcoidosis, granulomatous disease)
When ALP is elevated without liver disease:
- Bone disorders (Paget’s disease, bone metastases, hyperparathyroidism, recent fracture) – bone ALP is a major source
- Pregnancy – placental ALP rises throughout pregnancy and can more than double the normal range in the third trimester
- Growing children and adolescents normally have ALP 2-3 times adult levels due to bone growth
If ALP is elevated and it’s unclear whether the source is liver or bone, GGT helps distinguish: GGT is elevated in biliary disease but not in bone disease.
GGT – Gamma-Glutamyl Transferase
Normal range: approximately 9 – 48 U/L (men); 9 – 32 U/L (women)
GGT is an enzyme found in the liver, bile ducts, kidneys, and pancreas. It’s exquisitely sensitive to bile duct irritation and to alcohol exposure, making it useful in two specific contexts:
1. Clarifying the source of elevated ALP: If ALP and GGT are both elevated, the source is almost certainly hepatobiliary. If ALP is elevated but GGT is normal, bone disease is the more likely source.
2. Alcohol use: GGT is one of the most sensitive markers for chronic alcohol use. It rises with regular alcohol consumption and can remain elevated for 2-6 weeks after abstinence. While not diagnostic of alcoholism on its own, a persistently elevated GGT alongside an AST/ALT ratio above 2 strongly points toward alcohol-related liver disease.
GGT is also elevated by many medications, obesity, diabetes, and metabolic syndrome – so an isolated elevated GGT without other liver abnormalities doesn’t automatically indicate a serious problem.
Bilirubin – Direct and Total
Normal range: Total bilirubin 0.1 – 1.2 mg/dL; Direct bilirubin 0.0 – 0.3 mg/dL
Bilirubin is the yellow pigment produced when red blood cells break down. The liver processes it and excretes it into bile. Because bilirubin production, processing, and excretion all involve the liver and bile ducts, bilirubin elevation can reflect hepatocellular injury, cholestatic disease, or increased red blood cell breakdown.
On the LFT panel, bilirubin serves as both an injury marker and a functional marker – a rising bilirubin in advanced liver disease signals declining synthetic and excretory capacity.
- Predominantly elevated direct (conjugated) bilirubin: points to cholestasis or hepatocellular disease where processed bilirubin can’t be excreted
- Predominantly elevated indirect (unconjugated) bilirubin: points to increased red blood cell breakdown (hemolysis) or Gilbert syndrome – a benign genetic variant affecting roughly 1 in 10 people
The bilirubin article on this site covers the full breakdown in depth, including the three-zone pre-hepatic/hepatic/post-hepatic framework for diagnosis.
Albumin
Normal range: 3.5 – 5.0 g/dL
Albumin is the most abundant protein in blood plasma. It’s produced exclusively by the liver, at a rate that reflects the liver’s synthetic capacity. Because of albumin’s long half-life of approximately 20 days, it’s a marker of chronic rather than acute liver function. A patient with acute hepatitis can have normal albumin for weeks while ALT is dramatically elevated, because albumin made before the injury is still circulating.
When albumin begins to fall, it indicates that liver synthetic capacity has been impaired for a sustained period. Low albumin in liver disease is associated with disease severity and is one component of the Child-Pugh score used to stage cirrhosis.
Low albumin can also reflect malnutrition, protein-losing enteropathy (gut disease causing protein loss), nephrotic syndrome (kidney disease causing protein loss in urine), or severe inflammation – albumin is a negative acute-phase reactant and drops during significant illness even with intact liver function.
Total Protein
Normal range: 6.3 – 8.2 g/dL
Total protein includes albumin plus globulins (immune proteins and other proteins). It’s less specific than albumin alone for liver synthetic function. An elevated globulin fraction (calculated as total protein minus albumin) can indicate chronic infection, autoimmune disease, or multiple myeloma. A low total protein in the context of low albumin reinforces the picture of reduced liver synthesis or protein loss.
Prothrombin Time (PT) and INR
Normal INR: 0.8 – 1.2 (no anticoagulation)
As covered in the dedicated PT/INR article on this site, prothrombin time is the most sensitive acute marker of liver synthetic function. The clotting factors it measures – particularly factor VII with a half-life of only 4-6 hours – are all made by the liver. A rising PT in acute liver disease signals failing synthetic capacity within hours to days, making it a critical early warning sign in acute liver failure.
In chronic liver disease, PT/INR is part of both the Child-Pugh score and the MELD score (Model for End-Stage Liver Disease), which is used to prioritize liver transplant allocation.
Reading the Pattern: Two Dominant Injury Types
Most LFT abnormalities fall into one of two broad patterns – hepatocellular or cholestatic – and distinguishing them guides the next diagnostic steps.
| Feature | Hepatocellular Pattern | Cholestatic Pattern |
|---|---|---|
| Dominant elevation | ALT and AST | ALP and GGT |
| Bilirubin | May be elevated | Often elevated (direct) |
| Common causes | Hepatitis, NAFLD, alcohol, drugs | Gallstones, PBC, PSC, drugs |
| AST/ALT ratio | Variable | Usually normal or mildly elevated |
Some conditions produce a mixed pattern – elevated enzymes from both categories – which requires broader investigation.
Degree of elevation matters too:
- Mild elevation (1-3x upper limit of normal): very common, often NAFLD, medications, or benign transient causes
- Moderate elevation (3-10x): viral hepatitis, alcoholic hepatitis, drug reactions, autoimmune hepatitis
- Severe elevation (above 10x): acute viral hepatitis, ischemic hepatitis (“shock liver”), acetaminophen toxicity, acute biliary obstruction – these require urgent evaluation
Frequently Asked Questions
If my liver enzymes are elevated but I feel fine, should I be worried? Most mild elevations are discovered incidentally and in otherwise healthy, asymptomatic people often reflect NAFLD, a medication effect, or a transient cause like recent alcohol use or intense exercise. They warrant follow-up and investigation but rarely indicate an acute emergency. Your doctor will typically review the full pattern, ask about medications and alcohol, and likely repeat the test to confirm persistence before pursuing imaging or further workup.
Can supplements cause elevated liver enzymes? Yes – more often than people expect. Herbal supplements are a significant and underrecognized cause of drug-induced liver injury. Products containing kava, green tea extract, high-dose vitamin A, anabolic steroids, and certain weight loss or bodybuilding supplements have well-documented associations with liver damage. Always tell your doctor about supplements when liver enzymes are being investigated.
What does it mean if my albumin is low but my enzymes are normal? Low albumin with normal enzymes is worth investigating because it suggests a cause other than liver cell injury – malnutrition, protein loss through the kidneys (nephrotic syndrome) or gut (protein-losing enteropathy), or an inflammatory state. It can also be seen in advanced cirrhosis where enzyme levels have “burned out” but synthetic capacity is severely impaired.
How do I know if my elevated liver enzymes need imaging? Persistent elevation of liver enzymes – particularly ALT or ALP above 1.5-2 times the upper limit of normal on repeat testing – typically warrants liver ultrasound to assess for fatty liver, gallstones, bile duct dilation, or other structural abnormalities. Your doctor will decide based on the pattern, degree of elevation, and clinical context.
Can exercise raise liver enzymes? Yes. AST in particular can rise dramatically after intense exercise – particularly weightlifting – because skeletal muscle is rich in AST. ALT rises less markedly but can also be affected. If you exercised heavily in the 24-48 hours before your blood draw, mention it. A repeat test after a rest period can determine whether the elevation is exercise-related.
Disclaimer
This article is for educational purposes only and does not constitute medical advice. LFT results must be interpreted by a qualified healthcare provider in the context of your full clinical history, symptoms, medications, and other laboratory findings. Do not draw conclusions about liver health based on individual markers without professional evaluation.
References
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- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Liver tests. https://www.niddk.nih.gov/health-information/diagnostic-tests/liver-tests
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- MedlinePlus – National Library of Medicine. Liver function tests. https://medlineplus.gov/lab-tests/liver-function-tests/
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