Non‐alcoholic fatty liver disease: raising awareness of a looming public health problem

In Australia, there is a paucity of coordinated strategies for preventing, detecting, and managing NAFLD

Despite being the most frequent cause of chronic liver disease in Australia, the prevalence and clinical consequences of non‐alcoholic fatty liver disease (NAFLD) remain uncertain.1 Accurate population‐based data on the burden of NAFLD are crucial for guiding public health strategies and directing health care resources to reducing the incidence of NAFLD and associated metabolic conditions.

In their article published in this issue of the MJA, Roberts and colleagues report that the prevalence of NAFLD in regional Victoria is high; based on fatty liver index scores, the crude prevalence rate was 39%, the age‐ and sex‐standardised rate 36%.2 NAFLD is closely associated with components of the metabolic syndrome,3 and the prevalence of cardio‐metabolic risk factors in this rural sample was high, including obesity (36%), hypertension (55%), dyslipidaemia (44%), diabetes (12%), and metabolic syndrome (30%). The diagnosis of NAFLD requires the detection of hepatic steatosis and the exclusion of secondary causes, such as excessive alcohol use and other chronic liver diseases; excluding secondary causes of steatosis distinguishes NAFLD from the descriptive term “fatty liver”.4 In epidemiological studies, NAFLD can be inferred from the fatty liver index score,5 a clinical risk score based on body mass index, waist circumference, and serum γ‐glutamyltransferase and triglyceride levels. The prevalence of NAFLD in the four regional Victorian towns2 was higher than the estimated global prevalence of NAFLD diagnosed by liver imaging (about 25%6), probably reflecting the high frequency of comorbid metabolic conditions.

Once NAFLD is diagnosed, additional assessment of liver fibrosis severity is necessary for appropriate management decisions. Although most people with NAFLD do not develop clinically significant liver disease, as many as 10% develop advanced fibrosis and are at risk of complications of end‐stage liver disease and hepatocellular carcinoma emerging over 10‒20 years.7 The most important prognostic marker for adverse liver outcomes and overall mortality is advanced fibrosis, including bridging (stage 3) and cirrhosis (stage 4),7 which can be assessed with combinations of non‐invasive tests.8,9 In their population‐based study, Roberts and his colleagues found that 12.6% of people with NAFLD were at risk of advanced fibrosis, based on FibroScan liver stiffness measurements of 8 kPa or more. As noted by the study authors, their “findings confirm that NAFLD may become a significant public health problem during the next ten years.”2

The prevalence of NAFLD and the importance of liver fibrosis assessment are often not recognised by health care professionals and patients. As a consequence, advanced fibrosis or cirrhosis caused by NAFLD are often missed, and patients may present only after complications have developed, including liver cancer, by which time the therapeutic options are limited. Although screening the general population for NAFLD is not recommended, several clinical guidelines 4,10 advocate early detection of NAFLD in people at high risk — those with obesity, type 2 diabetes or metabolic syndrome — as these conditions are associated with increased risk of severe liver disease.

In Australia, there is a pressing need for a consensus statement on the assessment and management of NAFLD by primary care clinicians and specialists who treat patients with type 2 diabetes or other metabolic risk factors. Expert opinion recommends a pragmatic, two‐step pathway for assessing liver fibrosis severity in people with NAFLD. The first uses inexpensive simple fibrosis scores (NAFLD fibrosis score or Fibrosis‐4 index) to identify people at low risk of advanced fibrosis, who can be managed in primary care. These simple fibrosis scores combine routine biochemical tests with clinical risk factors for fibrosis; low scores have high negative predictive values for excluding advanced fibrosis.11 People with simple fibrosis scores indicating indeterminate or high risk need additional assessment with second‐step fibrosis tests, such as ultrasound elastography or serum enhanced liver fibrosis (ELF) tests. FibroScan has been validated for this fibrosis assessment step, but access to reliable tests for excluding advanced fibrosis in primary care can be difficult, and may require referral to secondary care. Irrespective of liver disease severity, all people with NAFLD should be evaluated for cardiovascular risk and metabolic conditions. Although Roberts and colleagues report high prevalence rates for metabolic risk factors in people with NAFLD, the inclusion of these factors in the fatty liver index used to identify NAFLD limits conclusions about their association.

The public health response to NAFLD in Australia is underdeveloped, with a paucity of coordinated strategies for preventing, detecting, and managing NAFLD. The study by Roberts and his colleagues raises awareness of the extent of NAFLD in regional Australia. Altering the course of this looming public health problem will require a coordinated, multidisciplinary approach from clinicians in primary care, liver clinics, and other specialities, as well as improved access to tests for assessing liver fibrosis and programs that facilitate healthy lifestyles and weight reduction.