ALT (Alanine Aminotransferase) Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is ALT (Alanine Aminotransferase)?

Alanine aminotransferase (ALT), sometimes referred to as SGPT (serum glutamic-pyruvic transaminase) in older literature, is an enzyme found predominantly in liver cells (hepatocytes). While small amounts exist in the kidneys, heart, and muscles, the liver contains by far the highest concentration — which is precisely what makes ALT such a specific marker for liver damage.

ALT plays a key role in amino acid metabolism. It catalyses the transfer of an amino group from alanine to alpha-ketoglutarate, producing pyruvate and glutamate. This reaction is part of the gluconeogenesis pathway — the process by which your liver manufactures glucose from non-carbohydrate sources, helping maintain blood sugar levels between meals.

Under normal circumstances, only small amounts of ALT leak from healthy liver cells into the bloodstream. When liver cells are damaged or destroyed — whether by infection, toxins, medications, or inflammation — ALT spills out in much greater quantities, causing blood levels to rise. This makes ALT one of the most sensitive indicators of hepatocellular injury.

Why Is ALT Tested?

ALT is a cornerstone of liver function testing and is requested in a wide range of clinical scenarios:

• Screening for liver disease: ALT is often the first marker to become elevated in conditions such as non-alcoholic fatty liver disease (NAFLD), viral hepatitis, and drug-induced liver injury.
• Monitoring hepatotoxic medications: Statins, methotrexate, anti-tuberculosis drugs, and certain anti-epileptics can cause liver damage. Regular ALT monitoring helps detect problems early.
• Investigating symptoms: Fatigue, jaundice, abdominal pain, dark urine, and unexplained nausea may prompt ALT testing.
• Viral hepatitis diagnosis and monitoring: ALT levels help assess the severity of hepatitis B and C infections and track response to antiviral treatment.
• Assessing alcohol-related liver disease: While AST typically rises more than ALT in alcoholic hepatitis (the AST:ALT ratio), ALT still plays an important role in the overall assessment.
• Metabolic health screening: Elevated ALT is increasingly recognised as an early marker of metabolic syndrome and insulin resistance, even before other features (such as raised blood glucose) become apparent.
• Pre-employment and insurance medicals: ALT is commonly included in routine health screening panels.

Normal ALT Ranges

ALT is measured in units per litre (U/L). Reference ranges have been debated in recent years, with some experts arguing that traditional upper limits are too high and miss early liver disease. The following ranges are used by most UK laboratories:

Group	Normal Range (U/L)
Adult men	10–49 U/L
Adult women	10–35 U/L
Children	10–40 U/L
Neonates	Up to 50 U/L (slightly higher is physiological)

Some hepatologists advocate for lower thresholds — 30 U/L for men and 19 U/L for women — based on research showing that even modestly elevated ALT within the traditional "normal" range correlates with increased risk of liver disease and cardiovascular mortality. If your ALT is in the upper part of the reference range, it may still be worth investigating, particularly if you have risk factors such as obesity, type 2 diabetes, or regular alcohol consumption.

ALT levels can fluctuate day to day. A single mildly elevated result does not necessarily indicate serious disease — your GP may repeat the test after 2–4 weeks before pursuing further investigation.

What Do High ALT Levels Mean?

Elevated ALT indicates that liver cells are being damaged. The degree of elevation can help narrow down the cause:

Mild elevation (1–3 times upper limit)

• Non-alcoholic fatty liver disease (NAFLD): The most common cause of mildly elevated ALT in the UK, affecting an estimated 20–30% of the adult population. NAFLD is strongly associated with obesity, type 2 diabetes, and metabolic syndrome.
• Alcohol-related liver disease: Chronic excessive alcohol intake causes a sustained, modest ALT rise.
• Medications: Statins, paracetamol (at therapeutic doses in some individuals), antibiotics, NSAIDs, and anti-epileptics can all raise ALT.
• Chronic hepatitis B or C: These viral infections can cause a persistent low-grade ALT elevation.
• Coeliac disease: Unexplained mild ALT elevation resolves with a gluten-free diet in many cases.
• Thyroid disorders: Both hypothyroidism and hyperthyroidism can affect ALT levels.
• Strenuous exercise: Intense physical activity, particularly resistance training, can cause a transient ALT rise that resolves within 7 days.

Moderate elevation (3–10 times upper limit)

• Acute viral hepatitis (A, B, C, E): Acute infection typically causes ALT to rise significantly.
• Autoimmune hepatitis: An immune-mediated attack on liver cells.
• Drug-induced liver injury (DILI): A more severe drug reaction than a mild elevation.
• Alcoholic hepatitis: An acute flare in the context of heavy drinking (though AST usually rises more than ALT).
• Bile duct obstruction: Gallstones or tumours can cause moderate ALT elevation alongside markedly raised ALP and bilirubin.

Severe elevation (more than 10 times upper limit)

• Acute viral hepatitis: ALT can exceed 1,000 U/L in severe acute hepatitis A or B.
• Paracetamol overdose: One of the most common causes of severe ALT elevation in the UK. This is a medical emergency.
• Ischaemic hepatitis: Sudden loss of blood supply to the liver (shock liver), seen in heart failure or hypotension.
• Autoimmune hepatitis flare: Severe exacerbations can push ALT above 1,000 U/L.
• Budd-Chiari syndrome: Hepatic vein thrombosis causing acute liver congestion.

What Do Low ALT Levels Mean?

Low ALT levels are generally not considered clinically significant and are not routinely investigated. However, some research has drawn associations between very low ALT and certain conditions:

• Vitamin B6 deficiency: ALT is a pyridoxal phosphate (vitamin B6)-dependent enzyme. Deficiency in B6 can reduce ALT activity. This is more common in elderly populations and those with poor dietary intake.
• Frailty and sarcopenia: Very low ALT in elderly patients has been associated with reduced muscle mass and increased frailty, likely because ALT is present in muscle tissue as well as the liver.
• Chronic kidney disease: Some studies have found lower ALT levels in patients on haemodialysis.
• Normal variation: Many healthy people have ALT at the lower end of the reference range without any clinical significance.

If your ALT is within or just below the reference range and you feel well, there is usually no cause for concern.

How to Improve Your ALT Levels

Since elevated ALT is far more common than low ALT, the focus here is on reducing raised levels:

Lifestyle changes

• Lose excess weight: Even a 5–10% reduction in body weight can significantly reduce ALT levels in people with NAFLD. A systematic review published in the Journal of Hepatology found that weight loss of 7% or more resolved steatohepatitis in the majority of patients.
• Reduce alcohol intake: If alcohol is the cause, reducing or eliminating consumption is the single most effective intervention. The liver has remarkable regenerative capacity — ALT levels can normalise within weeks of abstinence.
• Exercise regularly: Both aerobic exercise and resistance training reduce liver fat and ALT levels independently of weight loss. Aim for at least 150 minutes of moderate-intensity activity per week.
• Eat a Mediterranean-style diet: Rich in olive oil, oily fish, vegetables, legumes, and whole grains. This dietary pattern has been shown to reduce liver fat and ALT in clinical trials.
• Limit fructose and refined sugar: Excess fructose consumption (particularly from sugary drinks) drives hepatic fat accumulation.
• Drink coffee: Multiple large studies have found that coffee consumption (2–3 cups per day) is associated with lower ALT levels and reduced risk of liver fibrosis. The protective effect appears to be independent of caffeine content.

Medical review

• Review medications: If a drug is suspected, your GP may adjust the dose or switch to an alternative. Never stop prescribed medication without medical advice.
• Screen for hepatitis: If you have risk factors (travel, blood transfusion before 1991, injecting drug use), testing for hepatitis B and C is essential.
• Check for coeliac disease: A simple tTG antibody blood test can screen for coeliac disease, which is an underdiagnosed cause of elevated ALT.
• Investigate metabolic syndrome: Elevated ALT may be the earliest sign. Checking fasting glucose, HbA1c, lipid profile, and blood pressure can identify metabolic risk.

When Should You Get Tested?

Consider having your ALT levels checked if you:

• Are overweight or obese (BMI over 25)
• Consume alcohol regularly (more than 14 units per week)
• Have type 2 diabetes or metabolic syndrome
• Are taking medications known to affect the liver
• Experience fatigue, nausea, abdominal discomfort, or jaundice
• Have a family history of liver disease
• Have never been screened for hepatitis B or C
• Want a baseline health check, particularly if you are over 40

The NHS Health Check (offered every 5 years to adults aged 40–74) does not routinely include ALT testing, which means many people with early liver disease go undetected. Proactive testing is especially valuable given the rising prevalence of NAFLD in the UK.

Which Lola Health Tests Include ALT?

ALT is included in all Lola Health panels that assess liver function:

• Peak Insights (70 Biomarkers) — Comprehensive health screen with full liver function, metabolic markers, and more.
• Vital Check (56 Biomarkers) — Broad panel including ALT and other liver enzymes.
• Core Health (45 Biomarkers) — Essential health markers including a complete liver panel.
• Liver Health Blood Test — Focused panel for liver assessment including ALT, AST, ALP, GGT, bilirubin, and albumin.

All Lola Health tests use a venous blood draw at one of our nationwide partner clinics — never a finger prick. Results are reviewed by a doctor and returned within 4 working days.