Blood Work Education
LIVER FUNCTION
Understanding your liver panel -- ALT, AST, ALP, bilirubin, albumin, and more explained with clinical context.
Medically reviewed by Missy Zammichieli, DNP, APRN, FNP-BC ยท Updated March 2, 2026
THE BOTTOM LINE
- • Your liver panel is a window into how your liver is handling everything you throw at it -- food, alcohol, medications, supplements, and training stress.
- • A single elevated number doesn't mean your liver is damaged. Context matters: your workout schedule, what you're taking, and what the other markers look like alongside it.
- • If you train hard, AST can spike from muscle breakdown, not liver injury. An elevated AST with a normal ALT in an active person is more likely from your last workout than your liver.
- • Supplements are an underappreciated cause of liver enzyme elevations. If your numbers are off, bring your full supplement list to your appointment.
INTRODUCTION
Your liver processes everything you eat, drink, and take as medication. When something is stressing it, these markers are usually the first signal.
A liver panel is one of the most frequently ordered blood tests -- and one of the most commonly misunderstood. A single elevated enzyme doesn't necessarily mean your liver is damaged, and a completely normal panel doesn't guarantee the absence of liver disease. Context matters: your activity level, medications, supplements, body composition, hydration, and the timing of your last workout can all influence these results.
Fatty liver disease (your lab report may call this NAFLD or MASLD) affects approximately 25% of adults globally, making it the most prevalent chronic liver condition worldwide. Many of those people have no symptoms and no idea their liver is affected until routine bloodwork flags an abnormality.
YOUR BIOMARKERS EXPLAINED
ALT (Alanine Aminotransferase)
What it is: ALT is an enzyme found predominantly in liver cells, making it the most liver-specific enzyme on the panel. When liver cells are injured or inflamed, ALT leaks into the bloodstream.
Why it matters: ALT is the most sensitive single marker of liver cell injury and the primary screening enzyme for liver disease.
Reference ranges: Traditional ranges are approximately 7-56 U/L for men and 7-45 U/L for women. Updated research suggests tighter thresholds: roughly 30-33 U/L for men and 19-25 U/L for women as levels that should prompt further evaluation.
Common causes of elevation:
- • Fatty liver disease
- • Medications: acetaminophen (even at standard doses in some people), statins, certain antibiotics, antiepileptics
- • Alcohol use
- • Viral hepatitis (B and C)
- • Herbal and dietary supplements (discussed below)
- • Autoimmune hepatitis
- • Hemochromatosis (iron overload)
Note for active patients: ALT can rise modestly after intense exercise, though it's less affected by muscle damage than AST. If your ALT is mildly elevated and you trained heavily in the days before your blood draw, that's worth factoring in -- but persistent ALT elevation warrants investigation regardless of exercise habits.
AST (Aspartate Aminotransferase)
What it is: AST is an enzyme found in the liver but also in skeletal muscle, heart muscle, kidneys, and red blood cells. This makes it less liver-specific than ALT.
Why it matters: AST's real value depends on reading it alongside ALT. The AST:ALT ratio helps differentiate patterns of liver injury.
Reference ranges: Typically 10-40 U/L.
The AST:ALT ratio:
- • Below 1 is typical of fatty liver disease and most chronic hepatitis.
- • Above 2 is strongly suggestive of alcoholic liver disease; above 3 is highly specific.
- • Above 1 in known chronic liver disease may indicate progression to cirrhosis.
Exercise effects -- important for active people: AST is released from skeletal muscle during and after intense exercise, with elevations persisting 24-72+ hours. Research shows AST can spike significantly after high-intensity training even in people with perfectly healthy livers. If you do CrossFit, heavy lifting, or endurance events, this matters. An isolated AST elevation with a normal ALT is more likely muscle breakdown than liver injury. If there's uncertainty, creatine kinase (CK) can clarify -- if CK is also elevated, the AST is almost certainly muscular.
Alkaline Phosphatase (ALP)
What it is: ALP is an enzyme found in bile duct cells, bone, intestine, kidneys, and placenta. In the liver context, it reflects bile duct health and flow.
Why it matters: ALP helps distinguish between liver cell injury (ALT/AST-driven) and bile duct problems. An isolated ALP elevation raises a different set of possibilities than combined elevations.
Reference ranges: Typically 44-147 U/L in adults, with higher levels normal in adolescents and during the third trimester of pregnancy.
Interpreting ALP elevation:
- • Isolated ALP elevation: Consider bone disease, vitamin D deficiency, pregnancy, or normal growth in adolescents. GGT can confirm whether the source is the liver -- if GGT is also elevated, it's biliary.
- • ALP elevated with elevated ALT/AST: Suggests bile duct involvement alongside liver cell injury. Consider medication effects, infiltrative diseases, or biliary obstruction.
- • Significantly elevated ALP (>3x upper limit) with modest ALT/AST: Classic bile duct obstruction pattern -- think gallstones, strictures, or primary biliary cholangitis.
Bilirubin, Total
What it is: A yellow pigment produced from the normal breakdown of old red blood cells. The liver processes bilirubin so it can be excreted in bile.
Why it matters: Elevated bilirubin can reflect increased red blood cell breakdown, impaired liver processing, or blocked bile flow. Significantly elevated bilirubin causes jaundice -- yellowing of skin and eyes.
Reference ranges: Typically 0.1-1.2 mg/dL.
Common causes of elevation:
- • Gilbert's syndrome: A benign genetic condition affecting about 5-10% of the population. It causes mildly elevated bilirubin (typically 1-3 mg/dL) that fluctuates with fasting, stress, illness, and dehydration. It requires no treatment and has no clinical consequences -- some research even suggests the mildly elevated bilirubin may have antioxidant benefits.
- • Hemolytic anemias (increased red blood cell destruction)
- • Liver damage (acute hepatitis, cirrhosis)
- • Biliary obstruction (gallstones, tumors)
- • Medications (certain antibiotics, antivirals)
Practical note: If your bilirubin is mildly elevated but all other liver markers are normal and you feel fine, Gilbert's syndrome is the most likely explanation, especially if you've seen this pattern on previous blood draws.
Albumin
What it is: The most abundant protein in your blood, produced exclusively by the liver. Half-life of about 20 days.
Why it matters: Albumin reflects your liver's manufacturing capacity. Because of its long half-life, it doesn't change quickly -- low albumin generally indicates a chronic process, not something acute.
Reference ranges: Typically 3.5-5.5 g/dL.
What abnormal levels suggest:
- • Low albumin: Chronic liver disease (cirrhosis), malnutrition or inadequate protein intake, chronic illness or inflammation, nephrotic syndrome (protein loss through kidneys).
- • High albumin: Most commonly reflects dehydration rather than a real problem.
Key point: Mildly elevated liver enzymes alongside normal albumin typically mean the liver's core manufacturing function is intact. Elevated enzymes combined with low albumin raises concern for more advanced or chronic liver disease.
Total Protein
What it is: Total protein is the sum of albumin and globulins in the blood.
Reference ranges: Typically 6.0-8.3 g/dL.
Why it matters: Total protein by itself is a blunt instrument. Its value comes from looking at the albumin and globulin components individually. A normal total protein can mask an imbalanced ratio (e.g., low albumin offset by high globulins).
Globulin
What it is: A diverse group of proteins including antibodies, transport proteins, and inflammatory mediators. Calculated by subtracting albumin from total protein.
Reference ranges: Typically 2.0-3.5 g/dL.
What abnormal levels suggest:
- • High: Chronic infection, inflammation, autoimmune conditions, multiple myeloma, chronic liver disease.
- • Low: Immune deficiency, protein loss, certain genetic conditions.
Albumin/Globulin (A/G) Ratio
What it is: The ratio of albumin to globulin, calculated automatically by the lab.
Reference ranges: Typically 1.1-2.5.
What it reflects: A low ratio can mean decreased albumin production (liver disease, malnutrition) or increased globulin production (chronic inflammation, infection, autoimmune disease). A high ratio is generally not concerning.
GGT (Gamma-Glutamyl Transferase)
Note: GGT may or may not be on your specific panel, but it's commonly ordered alongside standard liver tests.
What it is: An enzyme found primarily in bile duct cells. Highly sensitive to biliary obstruction, liver injury, and alcohol use.
Reference ranges: Typically 0-51 U/L for men and 0-33 U/L for women.
Clinical utility:
- • Confirming the source of elevated ALP: If both ALP and GGT are elevated, the ALP elevation is likely from the liver rather than bone.
- • Alcohol use assessment: GGT rises with regular alcohol consumption and is one of the first enzymes to normalize with abstinence.
- • Fatty liver disease: GGT elevation has been associated with metabolic syndrome and fatty liver disease, independent of alcohol intake.
HOW THESE MARKERS TELL A STORY TOGETHER
Individual biomarkers are useful, but the real power comes from reading them as a pattern.
Liver cell injury pattern (ALT and AST elevated, ALP normal or mildly elevated): Direct injury to liver cells. Common causes: fatty liver disease, medication effects, viral hepatitis, autoimmune hepatitis. The AST:ALT ratio narrows it further -- below 1 favors non-alcoholic causes, above 2 favors alcoholic liver disease.
Bile duct pattern (ALP elevated, ALT and AST normal or mildly elevated): Bile duct obstruction or damage. Causes include gallstones, strictures, and certain medications. GGT elevation alongside ALP confirms the liver as the source.
Mixed pattern (all enzymes elevated): Something affecting both liver cells and bile ducts -- drug-induced liver injury, infiltrative diseases, or advanced liver disease.
Elevated enzymes with low albumin: Raises concern for chronic liver disease where the liver's protein-manufacturing capacity is compromised -- generally a longer-standing process.
All-normal panel: Reassuring, but early-stage fatty liver can exist with entirely normal enzymes.
WHAT AFFECTS THESE RESULTS
Exercise
Intense exercise causes muscle cell disruption, releasing enzymes into the bloodstream. AST is the most affected liver panel marker due to its high concentration in skeletal muscle -- elevations can last 24-72 hours post-exercise. ALT can also rise modestly. If you trained hard in the 48-72 hours before your blood draw, mention this to your provider.
Medications
Common medications that can elevate liver enzymes:
- • Acetaminophen (Tylenol): Most common cause of acute liver failure in the U.S. at high doses; can cause mild elevations at standard doses in some people.
- • Statins: Mild, typically transient ALT elevations in a small percentage of users. Current guidelines no longer recommend routine liver monitoring for statins.
- • Antibiotics: Amoxicillin-clavulanate is the most common antibiotic cause of drug-induced liver injury.
- • NSAIDs: Rarely cause liver cell injury.
Herbal and Dietary Supplements
An underappreciated cause. Supplements account for roughly 20% of drug-induced liver injury cases in the U.S., and that proportion is increasing. Common offenders: high-dose green tea extract, kava, comfrey, and multi-ingredient bodybuilding or weight-loss supplements. Because supplements aren't regulated like pharmaceuticals, actual contents may differ from labels. If your enzymes are unexpectedly elevated, a thorough supplement review is essential.
Alcohol
Alcohol is a direct liver toxin. Even moderate intake can elevate GGT, and heavier use affects AST preferentially (contributing to the elevated AST:ALT ratio described above). Effects are dose-dependent and can be compounded by obesity or concurrent medication use.
Body Composition and Metabolic Health
There is a well-established link between elevated BMI, insulin resistance, and ALT elevation. Metabolic syndrome components -- central adiposity, elevated triglycerides, insulin resistance -- are key drivers and underlie the high prevalence of fatty liver disease.
Fasting State and Hydration
Bilirubin can rise with prolonged fasting, which is particularly relevant for individuals with Gilbert's syndrome. Dehydration can falsely elevate albumin and total protein concentrations. Standard liver panels don't require fasting, but if your draw was part of a comprehensive metabolic panel that included glucose or lipids, you may have been fasting, which is worth noting.
COMMON QUESTIONS
"My AST is high but ALT is normal -- could it be from exercise?"
Yes -- one of the most common explanations in active people. AST is abundant in skeletal muscle, and intense training (eccentric loading, heavy lifting, CrossFit-style conditioning) can release significant amounts into the bloodstream. Your provider may order CK to confirm a muscular source, or recommend repeating the panel after 3-5 days of reduced training. Persistent elevation warrants further evaluation regardless.
"What is fatty liver disease?"
Excess fat accumulates in liver cells in people who don't drink heavily. It exists on a spectrum: from simple fat accumulation to an inflammatory form that can progress to scarring (fibrosis) and eventually cirrhosis. It affects roughly 25% of adults globally and is strongly associated with insulin resistance, obesity, and metabolic syndrome. Liver enzymes can be normal even with fatty liver present -- imaging (ultrasound or FibroScan) is often needed for diagnosis. Lifestyle changes -- particularly 7-10% body weight loss, regular exercise, and dietary improvements -- are the cornerstone of treatment.
"Do supplements affect liver enzymes?"
Yes, and sometimes significantly. High-dose green tea extract, multi-ingredient pre-workouts, fat burners, and certain herbal remedies have been linked to severe liver toxicity. If your liver enzymes are elevated, bring a complete supplement list (including brands and doses) to your appointment -- protein powders, pre-workouts, fat burners, herbal teas, all of it.
"How often should liver function be rechecked?"
For routine wellness monitoring, annual liver panels are standard. If an abnormality shows up, the recommendation is to repeat after addressing modifiable factors (alcohol, medications, supplements, exercise timing) -- typically 3-6 months for mild elevations. Persistent elevations warrant further workup: viral hepatitis testing, iron studies, autoimmune markers, and imaging. Your provider will set a recheck interval based on severity and your risk profile.
References
- 1. Trefts E, Gannon M, Wasserman DH. The liver. Curr Biol. 2017;27(21):R1147-R1151.
- 2. Younossi ZM, Koenig AB, Abdelatif D, et al. Global epidemiology of nonalcoholic fatty liver disease -- meta-analytic assessment of prevalence, incidence, and outcomes. Hepatology. 2016;64(1):73-84.
- 3. Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18-35.
- 4. Giannini EG, Testa R, Savarino V. Liver enzyme alteration: a guide for clinicians. CMAJ. 2005;172(3):367-379.
- 5. Prati D, Taioli E, Zanella A, et al. Updated definitions of healthy ranges for serum alanine aminotransferase levels. Ann Intern Med. 2002;137(1):1-10.
- 6. Nathwani RA, Pais S, Reynolds TB, Kaplowitz N. Serum alanine aminotransferase in skeletal muscle diseases. Hepatology. 2005;41(2):380-382.
- 7. Sorbi D, Boynton J, Lindor KD. The ratio of aspartate aminotransferase to alanine aminotransferase: potential value in differentiating nonalcoholic steatohepatitis from alcoholic liver disease. Am J Gastroenterol. 1999;94(4):1018-1022.
- 8. Pettersson J, Hindorf U, Persson P, et al. Muscular exercise can cause highly pathological liver function tests in healthy men. Br J Clin Pharmacol. 2008;65(2):253-259.
- 9. Whitfield JB. Gamma glutamyl transferase. Crit Rev Clin Lab Sci. 2001;38(4):263-355.
- 10. Fevery J. Bilirubin in clinical practice: a review. Liver Int. 2008;28(5):592-605.
- 11. Bosma PJ, Chowdhury JR, Bakker C, et al. The genetic basis of the reduced expression of bilirubin UDP-glucuronosyltransferase 1 in Gilbert's syndrome. N Engl J Med. 1995;333(18):1171-1175.
- 12. Busher JT. Serum albumin and globulin. In: Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Butterworths; 1990.
- 13. O'Connell TX, Horita TJ, Kasravi B. Understanding and interpreting serum protein electrophoresis. Am Fam Physician. 2005;71(1):105-112.
- 14. Ruhl CE, Everhart JE. Elevated serum alanine aminotransferase and gamma-glutamyltransferase and mortality in the United States population. Gastroenterology. 2009;136(2):477-485.
- 15. Chalasani N, Younossi Z, Lavine JE, et al. The diagnosis and management of nonalcoholic fatty liver disease: practice guidance from the AASLD. Hepatology. 2018;67(1):328-357.
- 16. Fontana RJ. Pathogenesis of idiosyncratic drug-induced liver injury and clinical perspectives. Gastroenterology. 2014;146(4):914-928.
- 17. Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC guideline on the management of blood cholesterol. J Am Coll Cardiol. 2019;73(24):e285-e350.
- 18. Navarro VJ, Khan I, Bjornsson E, et al. Liver injury from herbal and dietary supplements. Hepatology. 2017;65(1):363-373.
- 19. Ioannou GN, Boyko EJ, Lee SP. The prevalence and predictors of elevated serum aminotransferase activity in the United States in 1999-2002. Am J Gastroenterol. 2006;101(1):76-82.