Liver health: what your blood tests can tell you before problems develop

Non-alcoholic fatty liver disease and metabolic health

Non-alcoholic fatty liver disease, now more accurately referred to as metabolic dysfunction-associated steatotic liver disease (MASLD), is the most common liver condition in the UK and is closely linked to obesity, type 2 diabetes, insulin resistance and elevated blood lipids. Fat accumulates in liver cells when excess calories, particularly from refined carbohydrates and saturated fat, exceed the liver's capacity to process and export them. In its early stages, MASLD produces no symptoms and often no liver enzyme elevation at all, meaning that standard liver function tests can return normal results even when hepatic steatosis is already present. The key metabolic markers that indicate MASLD risk are elevated triglycerides, raised HbA1c or fasting glucose, elevated LDL cholesterol and rising ALT, assessed together rather than in isolation.

Alcohol and liver enzyme patterns

Alcohol is one of the most significant modifiable risk factors for liver disease in the UK. The liver preferentially metabolises ethanol, and when consumption is chronic or heavy, this process generates toxic byproducts that cause inflammation, fat accumulation and, over time, fibrosis. A characteristic pattern in alcohol-related liver disease is an AST:ALT ratio greater than 2, seen in approximately 70% of people with alcoholic liver damage. GGT (gamma-glutamyl transferase) is particularly sensitive to alcohol intake and rises reliably with regular consumption above 14 units per week, often before ALT or AST become abnormal. Regular monitoring of GGT alongside ALT and AST provides early visibility into alcohol's impact on liver health, before structural damage has occurred.

Medication monitoring: statins and other hepatotoxic drugs

Statins, anti-inflammatory medications, antibiotics, antidepressants and numerous other commonly prescribed drugs can elevate liver enzymes as a side effect. Statins are the most frequently monitored: mild ALT elevation is common and usually clinically insignificant, but persistent or significant elevation indicates the need for dose adjustment or an alternative. People who take long-term medications with known hepatotoxic potential benefit from regular liver enzyme monitoring, not only at the point of prescription, but as an ongoing health check. This is one of the most practical and underutilised reasons to include liver markers in a comprehensive blood panel.

Genetic liver conditions

Haemochromatosis, a genetic condition causing excessive iron absorption and accumulation in the liver, is one of the most common inherited liver disorders in Northern Europe, affecting approximately 1 in 150 people of Northern European ancestry at the genetic level (though clinical expression varies). Elevated ferritin and elevated transferrin saturation alongside abnormal liver enzymes raise suspicion for haemochromatosis. Wilson's disease causes copper accumulation and presents with abnormal liver enzymes, often in younger people. Non-alcoholic causes of persistently elevated ALT or AST should prompt consideration of genetic conditions, particularly in people without obvious metabolic risk factors.

Viral hepatitis

Hepatitis B and C are the most common causes of chronic viral liver disease globally, and both can be carried asymptomatically for years while causing progressive liver damage. In the UK, an estimated 215,000 people have chronic hepatitis B and around 80,000 have hepatitis C, with many undiagnosed. Persistently elevated ALT in the absence of alcohol, medication or metabolic causes warrants testing for hepatitis B surface antigen and hepatitis C antibody. This is particularly relevant for people with a history of intravenous drug use, blood transfusion before 1992, or healthcare work in countries with higher hepatitis prevalence.

Thyroid function and the liver

Hypothyroidism has a direct effect on liver metabolism: reduced thyroid hormone activity slows the processing of dietary fats, leading to elevated LDL cholesterol and triglycerides, both of which are risk factors for MASLD. Mild ALP elevation can also occur in hypothyroidism. In people with abnormal liver markers and elevated cholesterol who have no obvious explanation, thyroid function is worth investigating alongside the liver panel, as treating the thyroid dysfunction can normalise the liver picture.

The standard NHS liver function test, now more accurately called liver blood tests, measures a panel of enzymes and proteins: ALT, AST, ALP (alkaline phosphatase), GGT, albumin, total protein and bilirubin. Each provides different information:

ALT (alanine aminotransferase) is the most liver-specific enzyme. It is found predominantly in liver cells and rises when they are damaged or inflamed. The normal range is approximately 0-45 IU/L, though there is emerging evidence that even upper-normal ALT levels predict increased MASLD risk over time. ALT elevation with AST elevation roughly equally suggests non-alcoholic injury; when AST is elevated at more than twice the level of ALT, alcohol-related injury is more likely.

AST (aspartate aminotransferase) is also found in heart, muscle and other tissues, making it less liver-specific than ALT. Normal range is approximately 0-40 IU/L. It rises in liver injury but can also be elevated by vigorous exercise or muscle damage, which can produce false reassurance or false concern depending on context.

GGT (gamma-glutamyl transferase) is highly sensitive to alcohol consumption, certain medications and bile duct disease. It is often the first enzyme to rise with alcohol intake and the last to return to normal after abstinence, making it a useful marker for tracking the liver's response to alcohol reduction.

ALP (alkaline phosphatase) reflects mainly bile duct or bone activity. Elevated ALP with elevated GGT points toward bile duct obstruction or liver disease; elevated ALP with normal GGT is more likely to reflect bone rather than liver disease.

Albumin is produced by the liver and falls when liver synthetic function is impaired. Low albumin indicates compromised liver function and may also reflect malnutrition or chronic inflammatory states.

Bilirubin is a breakdown product of red blood cells, processed and excreted by the liver. Elevated bilirubin causes jaundice and may indicate liver cell damage, bile duct obstruction or increased red cell breakdown.

Cholesterol, triglycerides and HbA1c are not part of the standard liver function panel but are essential for understanding MASLD risk, since the metabolic drivers of fatty liver disease (dyslipidaemia, insulin resistance and elevated blood glucose) are the most modifiable factors in its prevention and progression.

For people with persistently elevated liver enzymes, further investigation through GP referral is appropriate: this may include ultrasound to assess hepatic steatosis or structural abnormalities, Fibroscan to estimate liver stiffness and fibrosis staging, or additional viral and genetic testing. Blood-based monitoring is a complement to imaging, not a substitute for it in cases where liver disease is already established.

Dietary approaches to reduce liver fat

The most evidence-supported dietary pattern for reversing early fatty liver disease is a Mediterranean-style diet: high in vegetables, legumes, wholegrains, olive oil and oily fish; low in refined carbohydrates, ultra-processed foods and red meat. A consistent finding across trials is that caloric restriction that reduces body weight by 5-10% measurably reduces hepatic fat content and improves liver enzyme profiles. Reducing refined sugar intake, particularly fructose from soft drinks and processed foods, is one of the most targeted single dietary changes for reducing hepatic fat accumulation.

Alcohol reduction and the liver

The liver has no lower safe threshold for alcohol when liver disease is already present. For people with elevated enzymes or established MASLD, reducing intake below 14 units per week (the UK guideline) is a minimum target; for those with confirmed fibrosis or cirrhosis, abstinence is typically recommended. GGT is a useful tracking marker: it typically falls significantly within 4-8 weeks of meaningful alcohol reduction, providing early feedback that the liver is responding.

Exercise and metabolic liver health

Both aerobic exercise and resistance training independently reduce hepatic fat content in people with MASLD, independent of weight loss. The mechanism involves improved insulin sensitivity, reduced systemic inflammation and increased fat oxidation in the liver. Even 150 minutes per week of moderate-intensity exercise shows measurable effects on liver enzyme profiles and hepatic fat over 3-6 months. Tracking ALT and metabolic markers before and after a sustained exercise programme is the most direct way to assess whether the liver is responding at a biochemical level.

Coffee and liver protection

Regular coffee consumption is one of the most consistently documented protective factors for liver health across the research literature. Multiple large cohort studies have found that consuming two or more cups per day is associated with lower rates of liver fibrosis, cirrhosis and liver cancer in people with established liver conditions. The mechanism appears to involve anti-inflammatory and antioxidant compounds in coffee beyond caffeine alone, as the protective effect is seen with both caffeinated and decaffeinated varieties. This is one of the most straightforward dietary recommendations with a solid evidence base for people concerned about liver health.