Autoimmune Hepatitis vs Fatty Liver: Key Differences

The difference between autoimmune hepatitis and fatty liver disease is fundamental: one is driven by immune dysfunction, the other by fat accumulation in liver cells. Autoimmune hepatitis (AIH) occurs when the immune system attacks the liver, causing progressive inflammation, while fatty liver disease results from metabolic or alcohol-related causes. Both conditions can lead to serious complications including cirrhosis, yet their symptoms, diagnostic pathways and treatments differ considerably. This article explains how each condition is diagnosed on the NHS, what symptoms to watch for, how each is treated, and whether both can occur together.

What is the difference between autoimmune hepatitis and fatty liver?

Autoimmune hepatitis is an immune-mediated inflammatory liver disease, while fatty liver disease results from fat accumulation linked to metabolic risk factors or alcohol. They have distinct causes, diagnostic features and treatments.

Autoimmune hepatitis and fatty liver disease are two distinct liver conditions with different underlying causes, mechanisms and long-term risks. Autoimmune hepatitis (AIH) is a chronic inflammatory condition in which the immune system mistakenly attacks the liver's own cells, causing progressive hepatocellular damage. Fatty liver disease, by contrast, results from an abnormal accumulation of fat (lipid) within liver cells, and is not driven by immune dysfunction.

Fatty liver disease is broadly divided into two categories:

• Metabolic dysfunction-associated steatotic liver disease (MASLD), the updated clinical term for what was previously called non-alcoholic fatty liver disease (NAFLD).^[1][2] NHS services and NICE guidance may still use the NAFLD terminology, and both terms refer to the same condition. MASLD is closely linked to obesity, type 2 diabetes, high blood pressure and raised cholesterol.

• Alcohol-related liver disease (ALD), caused by sustained excessive alcohol consumption.

Autoimmune hepatitis has no direct link to diet, alcohol or metabolic risk factors, though it is worth noting that AIH and MASLD can coexist, particularly as obesity becomes more prevalent, and this can complicate both diagnosis and management (discussed further below). AIH is more common in women and can occur at any age, including childhood. The condition is characterised by elevated liver enzymes, raised immunoglobulin G (IgG) levels and the presence of specific autoantibodies such as anti-nuclear antibody (ANA) and anti-smooth muscle antibody (ASMA).

In terms of progression, both conditions can lead to liver fibrosis and cirrhosis if left untreated, but the pathways differ significantly. AIH tends to progress more rapidly without immunosuppressive treatment, whereas fatty liver disease typically advances slowly over many years, often remaining asymptomatic for a long time. Understanding this distinction is important because the treatments for each condition are fundamentally different and should not be interchanged.

How are each condition diagnosed on the NHS?

AIH is diagnosed via autoantibody testing, raised IgG and liver biopsy, while MASLD is assessed using FIB-4 scoring, liver ultrasound and metabolic blood tests in line with NICE NG49.

Both autoimmune hepatitis and fatty liver disease are diagnosed through a combination of blood tests, imaging and, in some cases, liver biopsy, though the specific investigations differ between the two conditions. NHS diagnosis typically begins with a GP referral following abnormal liver function tests (LFTs) detected during routine blood screening or investigation of symptoms.

For autoimmune hepatitis, the diagnostic workup usually includes:

• Liver function tests showing elevated transaminases (ALT and AST)

• Raised serum immunoglobulin G (IgG)

• Autoantibody panel: ANA, ASMA, anti-liver kidney microsomal antibody (anti-LKM1)

• Liver biopsy, which remains the gold standard for confirming the diagnosis and assessing the degree of inflammation and fibrosis

• Exclusion of viral hepatitis (hepatitis B and C) and other liver conditions

The International Autoimmune Hepatitis Group (IAIHG) scoring system is a recognised tool that supports diagnosis alongside clinicopathological assessment, but it does not replace biopsy or specialist clinical judgement.^[5][6]

For fatty liver disease (MASLD/NAFLD), investigations typically follow a stepwise pathway in line with NICE guidance (NG49):

• Liver function tests (which may be normal in early disease)

• Fasting lipid profile, fasting glucose and HbA1c to assess metabolic risk

• Liver ultrasound, which can detect increased echogenicity consistent with steatosis

• Non-invasive fibrosis assessment using the FIB-4 score or NAFLD fibrosis score as a first step; where results are indeterminate or elevated, the Enhanced Liver Fibrosis (ELF) test or liver stiffness measurement (FibroScan/elastography) may be used as a second-line assessment

• Referral to secondary care is guided by fibrosis score thresholds set out in NICE NG49 and BSG/BASL guidance on abnormal liver blood tests

• Liver biopsy in selected cases where the degree of fibrosis or diagnosis remains uncertain

Early and accurate diagnosis is essential because misidentifying one condition as the other can lead to inappropriate treatment. Patients with suspected liver disease should be referred to a hepatologist or gastroenterologist for specialist assessment.

What symptoms should prompt you to see a doctor?

Persistent fatigue, jaundice, right upper abdominal discomfort, joint pain or dark urine should prompt a GP appointment, as both conditions can be silent until significant liver damage has occurred.

Both autoimmune hepatitis and fatty liver disease can be silent in their early stages, but certain symptoms should prompt a GP appointment. Many people with fatty liver disease have no symptoms at all until the condition has progressed to significant fibrosis or cirrhosis, which is why it is often detected incidentally during blood tests or abdominal imaging carried out for another reason.

Symptoms that warrant a GP review include:

• Persistent fatigue that is unexplained and does not improve with rest

• Right upper abdominal discomfort or a dull ache beneath the right ribcage

• Unexplained weight loss or loss of appetite

• Jaundice (yellowing of the skin or whites of the eyes)

• Dark urine or pale stools, which can indicate impaired bile flow

• Itching (pruritus) without an obvious skin cause

• Abdominal swelling (ascites), which may suggest advanced liver disease

• Joint pain, which can be an early feature of autoimmune hepatitis

Autoimmune hepatitis can sometimes present acutely, with a rapid onset of jaundice and markedly elevated liver enzymes, resembling acute hepatitis. In this situation, urgent assessment is needed and you should contact NHS 111 for guidance on the appropriate next step, or attend your GP as an urgent appointment.

If you develop sudden severe abdominal pain, confusion, or signs of bleeding such as vomiting blood or passing black tarry stools, these may indicate a serious complication of advanced liver disease and require immediate attendance at an emergency department (A&E) or a call to 999.

Routine monitoring of liver health is particularly important for people with known risk factors such as obesity, type 2 diabetes or a family history of liver disease.

How are autoimmune hepatitis and fatty liver disease treated?

AIH is treated with prednisolone and azathioprine; MASLD has no licensed UK pharmacotherapy and is managed through sustained weight loss, dietary change and optimising metabolic risk factors.

The treatments for autoimmune hepatitis and fatty liver disease are fundamentally different, reflecting their distinct underlying mechanisms.

Autoimmune hepatitis treatment follows hepatology guidelines (including EASL and BSG/BASL guidance) and typically involves:

• First-line induction therapy with prednisolone (a corticosteroid), often combined with azathioprine to allow steroid dose reduction over time^[10][11]

• Maintenance therapy with azathioprine alone in most patients who achieve remission

• Before starting azathioprine, testing for TPMT (thiopurine methyltransferase) or NUDT15 enzyme activity is recommended, as deficiency significantly increases the risk of serious bone marrow suppression

• Regular monitoring of full blood count (FBC) and liver function tests throughout treatment, to detect toxicity and assess treatment response

• Vaccination against hepatitis A and hepatitis B is recommended where patients are not already immune, as immunosuppression increases susceptibility to infection^[16][10]

• Bone protection measures (such as calcium, vitamin D supplementation and, where indicated, bisphosphonates) should be considered for patients on long-term corticosteroids, given the risk of steroid-induced osteoporosis^[16][10]

• Liver transplantation in cases of acute liver failure or end-stage cirrhosis that does not respond to medical therapy

If you experience suspected side effects from any of these medicines, you can report them to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Alcohol-related liver disease (ALD) treatment centres on:

• Complete alcohol cessation, which is the single most important intervention and can lead to significant improvement even in advanced disease

• Referral to local alcohol support services or structured alcohol treatment programmes

• Nutritional support, including thiamine (vitamin B1) supplementation where deficiency is suspected or confirmed, to reduce the risk of Wernicke's encephalopathy^[17]

• Management of complications such as ascites, variceal bleeding and hepatic encephalopathy by a specialist team

Fatty liver disease (MASLD/NAFLD) treatment currently has no licensed pharmacological therapy specifically approved in the UK for MASLD, though this is an active area of research. Management focuses on:

• Sustained weight loss of 7 to 10 per cent of body weight, which has been shown to reduce liver fat and inflammation (NICE NG49)

• Dietary modification, including a Mediterranean-style diet low in refined carbohydrates and saturated fat

• Regular physical activity, including both aerobic exercise and resistance training

• Optimising metabolic risk factors: blood pressure, blood glucose and lipid levels

• In people with type 2 diabetes, GLP-1 receptor agonists such as semaglutide may be considered in line with NICE guidance for type 2 diabetes management (NICE NG28) and, separately, for weight management where criteria are met (NICE TA875); these are not MASLD-specific indications, but weight loss and improved glycaemic control achieved through these treatments may benefit liver health

Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, as one option for people exploring medically supervised approaches to metabolic health alongside their NHS care.

Can you have both conditions at the same time?

Yes, AIH and fatty liver disease can coexist, particularly as obesity rates rise; distinguishing their contributions to liver injury requires specialist hepatology assessment and careful biopsy interpretation.

It is possible to have both autoimmune hepatitis and fatty liver disease simultaneously, and this overlap presents particular diagnostic and management challenges. The coexistence of the two conditions is sometimes referred to as an overlap syndrome, though this term more commonly describes the combination of autoimmune hepatitis with primary biliary cholangitis (PBC) or primary sclerosing cholangitis (PSC). The concurrent presence of metabolic steatotic liver disease alongside AIH is increasingly recognised as obesity rates rise in the general population.

When both conditions are present, distinguishing their relative contributions to liver injury can be difficult. Steatosis (fat accumulation) seen on biopsy in a patient with AIH may reflect true MASLD, the effect of corticosteroid therapy (which promotes weight gain and insulin resistance), or both. Conversely, elevated liver enzymes in a person with known fatty liver disease should not automatically be attributed to steatohepatitis without excluding autoimmune causes, particularly if the pattern of enzyme elevation or clinical features is atypical.

Management in this situation requires careful coordination between hepatology and, where relevant, endocrinology or metabolic medicine teams. Immunosuppressive therapy for AIH should generally be continued even when fatty liver disease is present, though the precise approach will be guided by specialist assessment and individualised to the patient's circumstances. Lifestyle interventions to reduce metabolic risk remain equally important. Corticosteroid use in AIH can worsen insulin resistance and promote weight gain, making dietary and physical activity support particularly valuable.^[16]

If you have a known liver condition and develop new or worsening symptoms, or if your liver function tests change unexpectedly, you should contact your GP or specialist team for review rather than assuming the change is explained by your existing diagnosis. Thorough reassessment is always preferable to diagnostic anchoring in liver disease.

Scientific References

1. A multisociety Delphi consensus statement on new fatty liver disease nomenclature.
2. Understanding the evolving nomenclature of steatotic liver disease.
3. Non-alcoholic fatty liver disease (NAFLD).
4. Hepatitis.
5. A diagnostic model of autoimmune hepatitis in unknown liver injury based on noninvasive clinical data.
6. Evaluation of Validity and Efficiency of Diagnostic Criteria in Autoimmune Hepatitis in Children.
7. Adequacy of scoring systems in diagnosing paediatric autoimmune hepatitis: retrospective study using a control group children with Hepatitis B infection.
8. Metabolic dysfunction-associated steatotic liver disease (MASLD/NAFLD): NICE guideline NG49.
9. Metabolic dysfunction-associated steatotic liver disease: recommendations for research (NG49).
10. British Society of Gastroenterology (BSG) guidelines for management of autoimmune hepatitis.
11. Comparative Efficacy of Mycophenolate Mofetil vs. Azathioprine in Autoimmune Hepatitis: A Systematic Review and Meta-Analysis.
12. An open-label randomised-controlled trial of azathioprine vs. mycophenolate mofetil for the induction of remission in treatment-naive autoimmune hepatitis.
13. Nudix hydrolase 15 deficiency and azathioprine toxicity in a liver transplant recipient: A case report.
14. Severe myelosuppression and alopecia after thiopurine initiation in a patient with NUDT15 deficiency.
15. Pharmacogenomic Assessment of Genes Implicated in Thiopurine Metabolism and Toxicity in a UK Cohort of Pediatric Patients With Inflammatory Bowel Disease.
16. EASL Clinical Practice Guidelines on the management of autoimmune hepatitis.
17. Alcohol-use disorders: diagnosis and management of physical complications (CG100).
18. GID-TA11477 draft scope: no medicines approved for MASLD or MASH in the UK.
19. Resmetirom (Rezdiffra) authorised to treat metabolic dysfunction-associated steatohepatitis (MASH) in adults.
20. Type 2 diabetes in adults: management (NG28) — summary of guidance for GLP-1 receptor agonists and tirzepatide.
21. Semaglutide for managing overweight and obesity (TA875).
22. Alcohol-related liver disease (ARLD).
23. Incidence and implications of abstinence-induced recompensation in alcohol-related cirrhosis.
24. Recompensation following first decompensation in patients with alcohol-related cirrhosis.

Frequently Asked Questions