Quick answer
A liver function test is a group of blood tests. The enzymes ALT and AST rise when liver cells are injured; ALP and GGT rise when bile flow is blocked; bilirubin, albumin and clotting time (PT/INR) show how well the liver is actually working. The ACG prefers the term "liver chemistries" because most of these measure injury, not function. Six of them come on every CMP, which costs $49 at Labcorp OnDemand. The pattern of which values rise, and by how much, matters more than any single number.
Liver function test markers and ranges
| Marker | What it shows | MedlinePlus range | Cleveland Clinic range |
|---|---|---|---|
| ALT | Enzyme mostly in liver cells; the most liver-specific | 4 to 36 U/L | 0 to 45 IU/L |
| AST | Enzyme in liver, muscle, heart and red cells | 8 to 33 U/L | 0 to 35 IU/L |
| ALP | Enzyme in bile ducts and bone | 20 to 130 U/L | 30 to 120 IU/L |
| GGT | Bile duct enzyme; rises with alcohol; confirms a liver source for high ALP | Varies by lab | 0 to 30 IU/L |
| Total bilirubin | Pigment the liver clears from old red cells | 0.1 to 1.2 mg/dL | 2 to 17 µmol/L |
| Albumin | Protein the liver makes; falls in long-term liver disease | 3.4 to 5.4 g/dL | 40 to 60 g/L |
| Total protein | Albumin plus globulins | 6.0 to 8.3 g/dL | 6.3 to 8.0 g/dL |
| PT / INR | Clotting time; the liver makes clotting factors | Separate test | PT 10.9 to 12.5 seconds |
How high is too high for ALT
This is where lab ranges and specialists disagree most. The 2017 ACG guideline says a true healthy normal ALT is 29 to 33 U/L for men and 19 to 25 U/L for women, that levels above this should be assessed, and that a raised ALT is linked with higher liver-related mortality.
MedlinePlus Medical Encyclopedia, Cleveland Clinic and the ACG 2017 guideline (upper limits shown from 0; the ACG gives 29 to 33 and 19 to 25 as the healthy upper limit).
So a woman with an ALT of 34 U/L may see no flag at one lab and still be above what the ACG calls healthy. That is a reason to mention it to your doctor, not to panic.
Patterns: hepatocellular vs cholestatic
The ACG defines hepatocellular injury as ALT and AST rising out of proportion to ALP, and cholestatic injury as ALP rising out of proportion to ALT and AST. Many clinicians put a number on it with the R ratio: (ALT divided by its upper limit) divided by (ALP divided by its upper limit).
| Pattern | What rises | R ratio | Common causes |
|---|---|---|---|
| Hepatocellular | ALT and AST far more than ALP | Over 5 | Fatty liver, viral hepatitis, alcohol, medicines, hemochromatosis, autoimmune hepatitis |
| Cholestatic | ALP and GGT far more than ALT | Under 2 | Gallstones or bile duct blockage, primary biliary cholangitis, some medicines |
| Mixed | Both | 2 to 5 | Medicines, infiltrative disease |
| Isolated bilirubin | Bilirubin only, mostly indirect | Gilbert syndrome (harmless), red cell breakdown | |
| AST at least 2 times ALT | AST more than ALT | Suggests alcohol-related liver injury | |
| AST and ALT with high CK | Enzymes plus muscle enzyme | Muscle injury or hard exercise, not the liver |
For a raised ALT, the ACG's evaluation list includes testing for hepatitis A, B and C, checking for fatty liver and alcohol use, screening for hemochromatosis (ferritin and iron saturation), autoimmune hepatitis, Wilson disease and alpha-1 antitrypsin deficiency, and reviewing all medicines and supplements.
How big is the rise?
| Category (ACG) | Times the upper limit | Example with a 35 U/L limit |
|---|---|---|
| Borderline | Under 2x | ALT under 70 |
| Mild | 2x to 5x | 70 to 175 |
| Moderate | 5x to 15x | 175 to 525 |
| Severe | Over 15x | Over 525 |
| Massive | ALT over 10,000 U/L |
Most abnormal results in otherwise well people are borderline or mild, and the most common cause in the US is fatty liver linked to weight, triglycerides and blood sugar.
Worked example: working out the pattern
A made-up result for a 46-year-old woman, lab upper limits ALT 35 and ALP 120 U/L:
- ALT 140 U/L, AST 70 U/L, ALP 95 U/L, bilirubin 0.8 mg/dL, albumin 4.4 g/dL
- ALT is 140 / 35 = 4.0 times the limit: a mild rise
- ALP is 95 / 120 = 0.79 times the limit
- R = 4.0 / 0.79 = 5.1: hepatocellular
- AST:ALT = 0.5: does not suggest alcohol
- Normal bilirubin and albumin: the liver is still doing its job
With triglycerides of 210 mg/dL and a waist that has grown, fatty liver is the most likely explanation, but her doctor would still check hepatitis B and C and iron studies and may order an ultrasound. A second case: ALP 260 and GGT 180 with a normal ALT. GGT confirms the ALP is coming from the liver rather than bone (MedlinePlus), and R is well under 2, a cholestatic pattern that usually leads to imaging of the bile ducts.
Preparation and false alarms
- Fasting: MedlinePlus says liver tests often need a fast only when run as part of a CMP.
- Exercise: heavy lifting or a long run in the day or two before can raise AST and ALT from muscle.
- Alcohol: raises GGT, and a recent binge can raise enzymes temporarily.
- Medicines and supplements: acetaminophen, statins, some antibiotics and many herbal products can raise enzymes; tell your doctor what you take.
- Growth and pregnancy: ALP is normally higher in teenagers and in late pregnancy because of bone and placenta.
People on GLP-1 medicines often track liver enzymes as weight falls; see GLP-1 blood tests and blood tests for weight loss.
Liver markers on SiPhox panels
| Marker | Heart & Metabolic | Ultimate 360 | GLP Optimization | Thyroid Focus | Kidney, Liver and Lp(a) kit |
|---|---|---|---|---|---|
| ALT | Yes | Yes | Yes | Yes | Yes |
| AST | Yes | Yes | Yes | Yes | Yes |
| ALP | Yes | Yes | Yes | No | No |
| GGT | No | Yes | Yes | No | No |
| Total bilirubin | Yes | Yes | Yes | No | Yes |
| Direct bilirubin | Yes | Yes | Yes | No | No |
| Albumin | No | Yes | Yes | No | Yes |
| Total protein | Yes | Yes | Yes | No | No |
| AST:ALT ratio | Yes | Yes | Yes | Yes | Yes |
| Covered | 7 of 9 | 9 of 9 | 9 of 9 | 3 of 9 | 5 of 9 |
Heart & Metabolic covers the enzymes and bilirubin but not GGT or albumin. Ultimate 360 and GLP Optimization cover the full set. None includes PT/INR. Capillary samples agree well with venous blood for ALT, AST, ALP and bilirubin in published studies of upper-arm devices; see are at-home blood tests accurate. The kidney function test guide covers the kidney markers on the same panels.
Which test to choose
| If you want | Test | Choose |
|---|---|---|
| A one-off check with glucose and electrolytes | CMP (6 liver tests) | Labcorp OnDemand, $49 |
| To investigate an abnormal result | Repeat panel plus hepatitis, iron and imaging | Your doctor |
| To track enzymes every 3 months with lipids and HbA1c | ALT, AST, ALP, bilirubin | SiPhox Heart & Metabolic |
| The full liver set with GGT and albumin | All liver chemistries plus iron studies | SiPhox Ultimate 360, or GLP Optimization on GLP-1 medicine |
Heart & Metabolic
Lipids plus kidney and liver function: the panel for cardiovascular and metabolic risk.
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Ultimate 360
Everything on the four core panels plus iron studies, B12 and folate, GGT and PSA.
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GLP Optimization
Built for people on GLP-1 medication: metabolic, liver, kidney, nutrient and iron markers.
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Frequently asked questions
What is included in a liver function test?
Usually ALT, AST, ALP, total (and sometimes direct) bilirubin, albumin and total protein. Many labs add GGT, and a clotting test (PT/INR) is ordered separately.
What is a normal ALT level?
Lab ranges run up to about 36 to 45 U/L. The American College of Gastroenterology says a truly healthy ALT is 29 to 33 U/L for men and 19 to 25 U/L for women.
Do you need to fast for a liver function test?
Not usually on its own. MedlinePlus says fasting is often needed only when the liver tests are part of a CMP, because of the glucose.
What causes elevated liver enzymes?
The most common causes are fatty liver, alcohol and medicines. Others include viral hepatitis, hemochromatosis, autoimmune liver disease and muscle injury, which raises AST.
Can I check my liver function at home?
Yes, for the main enzymes. SiPhox Heart & Metabolic reports ALT, AST, ALP and bilirubin; Ultimate 360 adds GGT and albumin. Share any abnormal result with your doctor.
Sources
- MedlinePlus: Liver function tests
- Cleveland Clinic: Liver function tests, normal ranges
- MedlinePlus Medical Encyclopedia: Comprehensive metabolic panel, normal values
- Kwo PY et al. ACG clinical guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol 2017
- MedlinePlus: Gamma-glutamyl transferase (GGT) test
- MedlinePlus: Bilirubin blood test
- MedlinePlus: Fasting for a blood test
- Labcorp OnDemand: Comprehensive metabolic panel (price and fasting)
- SiPhox Health: Heart & Metabolic panel page
- SiPhox Health: Ultimate 360 panel page
- SiPhox Health: Kidney, Liver and Lp(a) panel (12 markers, checked 30 Sep 2026)
- SiPhox Health panel comparison