How to Detect Fatty Liver Disease: Blood Tests & Scans | YEARS

How to Detect Fatty Liver Disease: Which Blood Tests and Examinations Actually Matter

A vague feeling of pressure in the upper right abdomen. Unexplained fatigue in the afternoon. Or simply the awareness that your lifestyle has not always been optimal over the past few years. Fatty liver disease is now one of the most common chronic liver conditions. It often causes no symptoms for a long time and can therefore remain undetected.

So how can fatty liver disease be identified before clinically relevant damage develops? Many people rely on standard liver tests performed by their general practitioner. Yet normal liver enzymes do not rule out fatty liver disease. Reliable assessment combines laboratory results, individual risk factors and – depending on the level of risk – non-invasive scores and imaging.

This article explains which diagnostic methods are informative, why traditional liver tests alone are insufficient, and how a comprehensive preventive assessment can provide additional clarity.

1. What is fatty liver disease? MASLD, MetALD and alcohol-related liver disease

Fatty liver disease, medically known as hepatic steatosis, occurs when excessive amounts of fat accumulate in liver cells. Histologically, steatosis has traditionally been defined as fat accumulation in more than 5% of hepatocytes. Modern imaging methods can also assess liver fat.

A new international nomenclature has been in use since 2023. The umbrella term is steatotic liver disease (SLD). Several categories are distinguished:

1. Metabolic dysfunction-associated steatotic liver disease (MASLD): Hepatic steatosis is present together with at least one cardiometabolic risk factor such as excess weight, abnormal glucose metabolism, hypertension or dyslipidaemia.
2. MetALD: A combination of metabolic risk factors and higher alcohol intake within the defined range for this category.
3. Alcohol-related liver disease (ALD): Alcohol plays the central aetiological role.
4. There are also forms of steatotic liver disease caused by specific conditions as well as rarer cryptogenic forms.

Until 2023, the metabolically driven condition was predominantly known as non-alcoholic fatty liver disease, or NAFLD. MASLD has largely replaced this term, although the diagnostic definitions are not completely identical.

The condition is highly prevalent. A large meta-analysis estimated the global prevalence of what was previously referred to as NAFLD at around 32% of the adult population. For Germany, the previous S2k guideline estimated that around 20 to 30% of adults were affected.

The good news is that liver fat can be substantially reduced, particularly during earlier stages, through targeted changes in body weight, diet, physical activity and metabolic risk factors.

2. Why early detection matters

The challenging aspect of fatty liver disease is its often silent course. Some people develop progressive liver disease over time:

1. MASLD with simple steatosis: Fat accumulation without pronounced inflammatory activity.
2. Metabolic dysfunction-associated steatohepatitis (MASH): Steatosis is accompanied by inflammatory and cellular changes.
3. Liver fibrosis: Progressive scarring of liver tissue may develop over time.
4. Liver cirrhosis: Advanced scarring substantially changes the structure and function of the liver.
5. Hepatocellular carcinoma (HCC): The risk rises particularly in people with advanced fibrosis or cirrhosis.

This progression is not inevitable. Some people remain stable for many years, some progress, and in others the disease can regress.

The most important prognostic factor for liver-related complications is the degree of fibrosis. Modern guidelines therefore place major emphasis on reliably excluding or detecting advanced fibrosis in people at elevated risk.

MASLD also matters beyond the liver. It is closely associated with type 2 diabetes, obesity, insulin resistance and cardiovascular disease. People with MASLD have, on average, a higher cardiovascular risk, with underlying metabolic risk factors playing a central role.

3. Fatty liver blood tests: What ALT, AST, GGT and other markers actually tell you

Traditional liver tests provide useful information, but they cannot reliably confirm or rule out fatty liver disease.

• ALT (alanine aminotransferase, also ALAT or GPT): ALT is found predominantly in liver cells. Elevated values can indicate liver cell injury. In MASLD, ALT may be elevated, but many people still have values within the reference range.
• AST (aspartate aminotransferase, also ASAT or GOT): AST is also found in cardiac and skeletal muscle. The AST-to-ALT ratio can provide additional clues. A markedly elevated AST/ALT ratio can occur in alcohol-related liver disease. AST may also rise relative to ALT as fibrosis progresses, but the ratio alone cannot establish a diagnosis.
• GGT (gamma-glutamyl transferase): GGT responds to many factors including alcohol intake, metabolic factors, medication and diseases affecting the liver or biliary system. An isolated elevation is therefore relatively non-specific.
• ALP (alkaline phosphatase): Particularly relevant for disorders affecting the bile ducts. It may remain normal in uncomplicated steatosis.
• Bilirubin: Typically does not rise in simple fatty liver disease and becomes more relevant in other or more advanced hepatobiliary disorders.

Markers reflecting the underlying metabolic situation are also important:

• HOMA-IR: Calculated from fasting glucose and fasting insulin and used as an indirect estimate of insulin resistance. It is included in the YEARS Core® programme.
• Triglycerides: Elevated values can be part of metabolic dysfunction and are frequently associated with MASLD.
• Ferritin: Can be elevated in metabolic dysfunction and MASLD. However, ferritin is non-specific and can also be influenced by inflammation or disorders of iron metabolism.

4. Why normal liver tests do not rule out fatty liver disease

This is one of the most important points: fatty liver disease can be present even when ALT, AST and GGT are within the reference range.

Studies have shown that a substantial proportion of people with imaging- or biopsy-confirmed steatotic liver disease have normal aminotransferase levels.

Fat accumulation does not necessarily lead to a significant release of liver enzymes into the blood. Even MASH and, in some cases, advanced fibrosis can occur despite normal transaminase levels.

Laboratory tests therefore provide valuable information but are not reliable exclusion tests. In people at elevated risk, non-invasive risk scores and – where appropriate – further testing are increasingly used.

5. Imaging for fatty liver disease: Ultrasound, FibroScan and MRI

Modern imaging enables non-invasive assessment of the liver.

• Ultrasound: The most widely used imaging method. Steatosis can appear as increased liver echogenicity. The examination is quick, relatively inexpensive and involves no ionising radiation. Sensitivity declines in mild steatosis, and severe obesity can limit image quality. Abdominal ultrasound including assessment of the liver is a standard part of the YEARS Core® programme.
• FibroScan or transient elastography: Primarily measures liver stiffness and therefore helps estimate the risk of fibrosis. Modern devices can also provide information about liver fat using the Controlled Attenuation Parameter, or CAP. The test takes only a few minutes and is non-invasive.
• MRI: Dedicated techniques such as MRI-PDFF (proton density fat fraction) are among the most precise non-invasive methods for quantifying liver fat. Quantitative fat measurement requires appropriate MRI sequences. Whole-body MRI can additionally identify structural changes, more pronounced hepatic steatosis and abnormalities in other organs.

A whole-body MRI should therefore not automatically be considered equivalent to dedicated MRI-PDFF. Diagnostic accuracy depends on the imaging protocol that is actually used.

6. Liver biopsy: When is it still necessary?

A liver biopsy allows direct microscopic assessment of steatosis, inflammation, cellular injury and fibrosis.

Its role has changed substantially due to advances in non-invasive testing. In many situations, the risk of advanced fibrosis can first be assessed using blood-based scores and elastography.

A biopsy may still be appropriate:

• in diagnostically unclear cases
• when other liver diseases need to be ruled out
• in selected patients with suspected clinically relevant MASH or advanced fibrosis
• as part of certain clinical trials or treatment decisions

For routine initial assessment of suspected MASLD, biopsy is not required in many patients. At YEARS, the focus is on non-invasive diagnostics.

7. Scores and calculation tools: FLI, FIB-4 and NAS

Clinical scores can help estimate the probability of steatosis or the risk of advanced fibrosis.

Fatty Liver Index (FLI)

The FLI combines:

• BMI
• Waist circumference
• GGT
• Triglycerides

Traditional thresholds are:

• FLI <30: Fatty liver disease is less likely.
• FLI >60: Fatty liver disease is more likely.

The score was developed as a simple screening tool but does not replace individual medical assessment.

FIB-4 Score

The FIB-4 score is particularly relevant in current clinical practice. It is calculated using age, AST, ALT and platelet count and is primarily used to estimate the risk of advanced fibrosis.

For many adults:

• FIB-4 <1.3: low risk of advanced fibrosis
• FIB-4 between 1.3 and 2.67: intermediate range; further testing is often appropriate
• FIB-4 >2.67: elevated risk requiring further evaluation

Interpretation is age-dependent. Different cut-offs may apply in older adults, while its diagnostic value is more limited in younger people.

Current European guidelines recommend a stepwise approach for people with MASLD or elevated risk: an established blood-based score such as FIB-4 is used first, followed by further testing such as liver elastography when the risk is elevated or unclear.

NAS Score

The NAFLD Activity Score, or NAS, is derived from liver biopsy findings and assesses histological features such as steatosis, inflammation and cell injury. It is not suitable as a non-invasive screening tool.

8. Who should be assessed for fatty liver disease?

Intensive liver screening of all asymptomatic adults is not recommended. However, targeted assessment can be useful in people with specific risk profiles.

Particularly important risk factors include:

• Overweight or obesity, especially visceral adiposity
• Type 2 diabetes
• Insulin resistance or prediabetes
• Metabolic syndrome
• Hypertension
• Elevated triglycerides and other forms of dyslipidaemia

Other possible factors include:

• Higher alcohol consumption
• Certain medications
• Polycystic ovary syndrome
• Certain endocrine disorders

People with a normal body weight can also develop metabolically driven fatty liver disease. Normal weight does not rule out an unfavourable fat distribution or metabolic dysfunction.

The overall risk profile therefore matters more than BMI alone.

9. Detecting fatty liver disease early at YEARS: Our diagnostic approach

At YEARS, we assess liver health within the broader context of metabolic health and other risk factors. The diagnostic programme is non-invasive and designed around early detection.

The YEARS Core® programme (€1,900) includes:

• Liver and metabolic markers: including ALT, AST and GGT, as well as metabolic markers such as fasting glucose, fasting insulin and HOMA-IR, ferritin and a detailed lipid profile including triglycerides.
• Ultrasound imaging: The abdominal ultrasound includes assessment of liver structure for signs of steatosis and other abnormalities.

For a broader structural assessment, the YEARS Evolve® programme (€7,600) additionally includes:

• Whole-body MRI: The MRI protocol assesses numerous organ systems and can detect structural changes in the liver as well as relevant steatosis. Quantitative liver fat measurement requires appropriate dedicated sequences.
• Extended metabolic panel: More than 120 biomarkers allow a broader metabolic assessment.

All results are brought together in the YEARS Health Report and reviewed by a physician. If there are signs of relevant liver disease or an elevated risk of fibrosis, targeted hepatological or gastroenterological diagnostics may subsequently be required.

Please note: YEARS diagnostics are a preventive service focused on early detection and do not replace specialised hepatological or gastroenterological assessment in patients with known advanced liver disease.

10. Detecting fatty liver disease requires more than one blood test

Fatty liver disease cannot be reliably assessed using a single laboratory marker. What matters is the combination of metabolic risk profile, laboratory values and – depending on individual risk – validated scores and appropriate imaging.

The key message remains simple: normal liver enzymes do not rule out MASLD.

People with relevant risk factors should therefore discuss with their physician whether further risk stratification is appropriate. A comprehensive check-up can bring together laboratory values, metabolic markers and imaging and ensure that abnormal findings are followed up appropriately.

Book a consultation at YEARS or compare our diagnostic programmes.

Frequently Asked Questions

Can you have fatty liver disease even if your liver tests are normal?

Yes. A substantial proportion of people with MASLD have normal transaminase levels. Even more advanced changes can sometimes occur despite normal ALT and AST. Normal liver tests are therefore not sufficient to reliably exclude fatty liver disease or clinically relevant fibrosis.

Which blood test detects fatty liver disease most reliably?

There is no single reliable blood marker. ALT, AST and GGT provide useful information but need to be interpreted alongside metabolic risk factors and other investigations. FIB-4 now plays an important role in estimating fibrosis risk.

When is ultrasound useful if fatty liver disease is suspected?

Ultrasound can be useful in people with abnormal liver tests, metabolic risk factors or another clinically justified suspicion. It performs well in more pronounced steatosis but is less sensitive for mild disease. Additional methods such as elastography may be required to assess fibrosis.

Is fatty liver disease reversible, and how quickly can it improve?

Yes. Simple steatosis in particular can improve substantially through weight loss, exercise, dietary changes and better control of metabolic risk factors.

A weight reduction of approximately 5% can already reduce liver fat. Larger weight losses of around 7 to 10% are more often associated with improvements in inflammatory changes; with greater weight reduction, the probability of fibrosis regression also increases. Individual outcomes depend on disease stage and other risk factors.

This article is intended for general information only and does not replace individual medical advice, diagnosis or treatment. The information reflects the scientific evidence available at the time of publication.

Sources

• Bedogni, G., Bellentani, S., Miglioli, L., et al. (2006). The Fatty Liver Index: a simple and accurate predictor of hepatic steatosis in the general population. BMC Gastroenterology, 6, 33.
• EASL–EASD–EASO. (2024). Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD). Journal of Hepatology, 81(3), 492–542.
• Fracanzani, A. L., Valenti, L., Bugianesi, E., et al. (2008). Risk of severe liver disease in nonalcoholic fatty liver disease with normal aminotransferase levels: a role for insulin resistance and diabetes. Hepatology, 48(3), 792–798.
• Rinella, M. E., Lazarus, J. V., Ratziu, V., et al. (2023). A multisociety Delphi consensus statement on new fatty liver disease nomenclature. Journal of Hepatology, 79(6), 1542–1556.
• Riazi, K., Azhari, H., Charette, J. H., et al. (2022). The prevalence and incidence of NAFLD worldwide: a systematic review and meta-analysis. The Lancet Gastroenterology & Hepatology, 7(9), 851–861.