ALT (SGPT) Blood Test Checker

What is an ALT (SGPT) blood test?

ALT (alanine aminotransferase) is an enzyme found mainly inside liver cells. When liver cells are irritated or damaged, ALT leaks into the bloodstream, so a raised ALT is one of the most sensitive signs of liver-cell injury. You may also see it called SGPT (serum glutamic-pyruvic transaminase) – the older name for exactly the same test. ALT and SGPT are the same thing.

ALT is usually measured as part of a liver function test (LFT) panel or a comprehensive metabolic panel (CMP), alongside:

• AST (SGOT) – aspartate aminotransferase, found in liver but also in muscle, heart and red cells.
• ALP – alkaline phosphatase, from bile ducts and bone.
• GGT – gamma-glutamyl transferase, from bile ducts; raised by alcohol and some medicines.
• Bilirubin – a breakdown product of haemoglobin processed by the liver.
• Albumin and sometimes INR – measures of the liver's synthetic function.

The checker above shows how your ALT compares with the upper limit of normal – either the healthy upper limits recommended by the American College of Gastroenterology (ACG) or your own lab's limit if you enter it – grades the elevation as borderline, mild, moderate or severe, and, if you add AST, calculates the AST/ALT (De Ritis) ratio.

ALT normal range

There are two kinds of "normal" for ALT, and they differ more than for most tests:

The ACG guideline points out that many laboratory reference ranges were built from populations that included people with undiagnosed fatty liver disease, which pushed the upper limits up. Using lower, "healthy" limits catches more people with early liver disease. That is why an ALT of 38 U/L might be "normal" on your report but above the ACG upper limit, especially for a woman.

ALT is reported in U/L (units per litre) in most countries. Some European laboratories report µkat/L: 1 µkat/L ≈ 60 U/L. The checker accepts either.

How high is high? Grading ALT elevations

The ACG grades liver enzyme elevations by multiples of the upper limit of normal (ULN):

Worked examples

• ALT 28 U/L (man): within the ACG healthy upper limit of 33 U/L.
• ALT 64 U/L, AST 41 U/L (man): 1.9× the ACG limit – borderline; AST/ALT ratio 0.64, typical of fatty liver disease.
• ALT 52 U/L, AST 118 U/L: AST/ALT ratio 2.3 – a pattern classically associated with alcohol-related liver disease (or muscle injury).
• ALT 640 U/L, AST 410 U/L (man): about 19× the ACG limit – severe acute liver injury; same-day medical review.

Common causes of a high ALT

Metabolic dysfunction-associated steatotic liver disease (MASLD)

Formerly called non-alcoholic fatty liver disease (NAFLD), this is now the most common cause of a mildly raised ALT in many countries. Fat builds up in the liver in association with excess weight, type 2 diabetes, high triglycerides and high blood pressure. ALT is usually only mildly raised, and the AST/ALT ratio is usually below 1 – until fibrosis develops, when AST tends to rise relative to ALT. A normal ALT does not exclude fatty liver.

Alcohol

Alcohol can raise ALT and particularly AST and GGT. An AST/ALT ratio of 2 or more is a classic (though not definitive) clue to alcohol-related liver disease.

Medicines and supplements

Many medicines can raise ALT, from common painkillers and antibiotics to cholesterol-lowering statins, anti-seizure medicines and anti-tuberculosis drugs. Herbal and dietary supplements – including some bodybuilding, weight-loss and "detox" products and green-tea extract – are increasingly recognised causes. Do not stop a prescribed medicine on your own; discuss any rise with your prescriber.

Viral hepatitis

Hepatitis B and C cause chronic, often silent ALT elevations and are tested for in most liver screens. Hepatitis A and E cause acute hepatitis with high ALT that usually resolves.

Other causes

ALT, AST and the pattern of liver injury

Clinicians look at which liver tests are raised, not just how high:

The ACG guideline uses the R ratio to formalise this: R = (ALT ÷ ALT ULN) ÷ (ALP ÷ ALP ULN). An R above 5 suggests a hepatocellular pattern, below 2 a cholestatic pattern, and 2–5 a mixed pattern.

The AST/ALT (De Ritis) ratio

AST and ALT, together with age and platelet count, also feed into the FIB-4 score, which estimates the likelihood of advanced liver scarring – see the FIB-4 calculator.

Why ALT is in your liver – and why it leaks

ALT's job inside liver cells is to move an amino group from the amino acid alanine to a molecule called alpha-ketoglutarate, a step that links protein and sugar metabolism. It works in the fluid (cytoplasm) of the liver cell. When the cell membrane is damaged or becomes leaky, ALT escapes into the blood, where it is cleared over roughly two days. So:

• ALT reflects ongoing liver-cell injury, not how well the liver is working. A person with severe scarring (cirrhosis) can have a normal ALT because few active liver cells remain to leak enzyme.
• The height of ALT does not equal the severity of liver disease. Acute hepatitis A can produce an ALT in the thousands and resolve completely, while chronic hepatitis C may cause only mild elevations for decades while scarring progresses.
• Changes over time – a falling ALT after stopping a medicine or alcohol, for example – are often more informative than a single value.

The liver's actual function is assessed by albumin, bilirubin and clotting tests such as INR, along with platelet count and imaging.

Other tests on a liver panel

ALT is rarely ordered on its own. It is usually part of a liver panel or a comprehensive metabolic panel (CMP), and the other results help explain what a raised ALT means:

Clinicians distinguish liver enzymes (ALT, AST, ALP, GGT), which indicate injury, from true liver function tests (bilirubin, albumin, INR), which show how well the liver is working. A raised ALT with normal bilirubin, albumin and INR usually means the liver is still working normally.

FIB-4: from ALT to a fibrosis estimate

When ALT is raised because of fatty liver disease, the most important question is often whether there is scarring (fibrosis). The FIB-4 index combines four routine values (try the FIB-4 calculator):

FIB-4 = (age × AST) ÷ (platelet count × √ALT)

with AST and ALT in U/L and platelets in 10⁹/L. In adults with MASLD, a FIB-4 below 1.3 suggests a low likelihood of advanced fibrosis, while a value above 2.67 suggests a higher likelihood and usually prompts further assessment, such as elastography or a specialist review. Values in between are indeterminate. FIB-4 is less reliable in people under 35 and over 65, and it was not designed for acute hepatitis. Notice that ALT appears in the denominator: a higher ALT alone does not raise FIB-4 – it is the combination with AST, age and platelets that matters.

Factors that influence ALT

Fatty liver disease and the new terminology

In 2023 an international group of liver societies agreed new names: metabolic dysfunction-associated steatotic liver disease (MASLD) replaced NAFLD, and MASH (metabolic dysfunction-associated steatohepatitis) replaced NASH. The change reflects that fatty liver is driven mainly by metabolic factors – excess weight, insulin resistance, type 2 diabetes, high blood pressure and abnormal lipids. A new category, MetALD, covers people with metabolic risk factors who also drink alcohol above certain thresholds. You may see either set of terms on reports and in articles.

What usually happens after a raised ALT

For a mild elevation in someone who feels well, the ACG guideline approach is broadly:

1. Repeat the test to confirm the rise is persistent, after avoiding alcohol and strenuous exercise.
2. Review alcohol intake, medicines and supplements.
3. Check for common causes: hepatitis B and C tests, iron studies, metabolic risk factors (glucose/A1C, lipids, weight), and sometimes thyroid and coeliac tests.
4. Liver ultrasound to look for fatty liver and other changes.
5. Fibrosis assessment with FIB-4 or elastography in fatty liver disease.
6. Referral to a liver specialist if the cause is unclear, the elevation is moderate or severe, or there are signs of advanced disease.

Severe elevations need much quicker action, the same day if the person is unwell.

How to prepare for an ALT test

• No fasting is usually needed for ALT itself, though it is often measured with tests that do require fasting.
• Avoid strenuous exercise for a day or two beforehand – heavy weight training can raise AST and ALT.
• Avoid alcohol for a few days if your clinician is trying to establish a baseline.
• List all medicines and supplements, including herbal products.

Symptoms

Most people with a raised ALT have no symptoms – it is usually found on routine tests. Liver injury severe enough to cause symptoms may produce tiredness, nausea, pain under the right ribs, dark urine, pale stools, itching or jaundice (yellow skin or eyes).

Seek urgent care if you have jaundice, confusion, vomiting blood, black stools, a swollen abdomen, or if you may have taken too much paracetamol (acetaminophen) – even if you feel well, because liver damage from paracetamol can be silent at first.