CASL Advocacy Letter on Importance of AST in Non-Invasive Screening Strategies for MASLD-Related Liver Fibrosis

Dear Members of INESSS,

On behalf of the Canadian Association for the Study of the Liver (CASL), we are writing to commend your continued leadership in promoting the judicious use of biomedical analyses across Québec’s healthcare system. We strongly support efforts to optimize resource utilization while maintaining high standards of patient care.

We wish, however, to highlight an important and evolving clinical context in which the role of aspartate aminotransferase (AST) is both essential and evidence-based: the non-invasive screening of liver fibrosis in individuals at risk of metabolic dysfunction–associated steatotic liver disease (MASLD), including people living with diabetes, obesity, HIV, and other high risk populations.

As outlined in your clinical tool, AST is appropriately recognized as a component of validated fibrosis scores, including FIB-4. In recent years, the FIB-4 index has emerged as a cornerstone of first-line risk stratification for liver fibrosis, endorsed by all major international and national guidelines, including those from CASL, AASLD, EASL, and most recently, Diabetes Canada.

FIB-4 integrates AST, ALT, age, and platelet count into a simple, widely accessible, and low-cost tool that enables early identification of individuals at risk for advanced liver fibrosis. Its use is now firmly embedded in clinical pathways for populations at increased risk, including individuals with type 2 diabetes, obesity, and other cardiometabolic conditions. Importantly, the most recent Diabetes Canada guidelines—developed with leadership from CASL—explicitly recommend the use of FIB-4 as a first-line screening strategy in these high-risk populations.

In this context, AST is not a redundant or optional biomarker, but rather a critical component of an evidence-based, validated, and guideline-endorsed screening algorithm. Unfortunately, ALT alone is not an accurate test to rule-out liver fibrosis, as 20% of patients with advanced liver fibrosis have persistently normal ALT. As such, FIB-4 is essential and widely recommended by scientific societies. Restricting access to AST outside of narrowly defined indications risks undermining the implementation of these widely recommended care pathways.

From a health system perspective, the use of FIB-4 is highly aligned with the principles of value-based care. It is:

• Cost-effective, leveraging routinely available laboratory tests
• Scalable, enabling population-level screening in primary care
• Efficient, reducing unnecessary referrals for specialized imaging or invasive procedures
• Clinically impactful, allowing earlier identification and management of individuals at risk of advanced liver disease

Given the growing burden of MASLD—now the most prevalent liver disease in Canada, affecting 32% of the general population—and its strong association with cardiometabolic conditions, the implementation of simple, accessible, and validated screening tools such as FIB-4 is a public health priority.

We therefore respectfully suggest that the current framing of AST use be clarified to explicitly recognize its essential role within validated fibrosis scoring systems, particularly FIB-4, when used in guideline-directed screening strategies for MASLD-related liver fibrosis. Such clarification would support clinicians in aligning practice with contemporary evidence and ensure that efforts to reduce low-value testing do not inadvertently limit access to high-value, guideline-endorsed care.

CASL remains fully committed to collaborating with INESSS and partners across Québec to advance evidence-based, equitable, and sustainable liver care. We would welcome the opportunity to contribute to future updates of this clinical tool and to support the integration of MASLD screening pathways into routine clinical practice.

Sincèrement,
Giada Sebastiani
President of the Canadian Association for the Study of the Liver