**1. Introduction**

Autism spectrum disorder (ASD) is a developmental disorder with a variable phenotypic expression characterized by communication and socialization difficulties and repetitive and stereotyped patterns of behavior [1,2]. ASD is generally diagnosed in early childhood and is considered to be secondary to an alteration in early brain development and neural reorganization [3]. The core symptoms of ASD have an early onset in childhood and tend to persist throughout the lifespan.

The global estimated prevalence of ASD is 1–2% [4]. In Argentina there is a lack of data on the overall prevalence of ASD; however, isolated studies have found similar figures to the prevalence estimates for the Americas by the World Health Organization (WHO) 0.7% [5,6].

Early diagnosis of ASD guides individualized early intervention. ASD diagnostic assessment warrants a detailed evaluation of the behavioral features described in manuals of diagnosis and classification, including the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) [7] and the International Statistical Classification of Diseases and Related Health Problems 10th revision [8]. However, a timely diagnosis of ASD should be complemented with a comprehensive assessment of functional needs performing everyday life activities, to ensure meaningful and adequate interventions.

In 2001 the WHO proposed the use of the International Classification of Functioning, Disability, and Health (ICF) [9] to describe functioning and disability from a biopsychosocial perspective. *Functioning* is an umbrella term to describe what a person with a health condition does or is able to do in everyday life at home, school, and in the community [9,10]. In 2007 a Child and Youth version of the ICF (ICF-CY) [11] was published specifically to capture functioning in developing individuals by adding and expanding on the descriptions of categories provided in the ICF. The ICF-CY facilitates the description of functional *abilities* and limitations in each area of development, promoting a family/child-centered approach [11]. This is important because children with neurodevelopmental disorders and their families cherish the child's functional abilities rather than the physical challenges, limitations, and participation restrictions associated with a specific diagnosis [12].

Moreover, the ICF systematically incorporates the role of environmental factors, including family, friends, therapists, societal attitudes, services, health systems and policies, and products and technology, as essential elements that facilitate or hinder participation and social inclusion [9,11]. Additionally, all content in the ICF is in conformity with international conventions and declarations on the rights of children and persons with disabilities, encouraging a human rights-based approach [9,11].

The ICF structures health and health-related domains into a hierarchy starting with components, then chapters, followed by categories. An ICF category is represented by an alphanumeric code. This code contains a letter that denotes one of the components of the ICF: body functions (b), body structures (s), activities and participation (d), and environmental factors (e) [9,11]. The component index letters are followed by a numeric code starting with the chapter number adding one digit (e.g., b**1** mental functions), followed by a second-level category code adding two digits (e.g., b1**67** mental functions of language), and third and fourth level code by adding one digit respectively (e.g., b167**0** reception of language and b1670**0** reception of spoken language). The categories with their corresponding codes must be completed with a qualifier: one, or more numbers after a point which denotes the severity of the problem or the extent to which a factor is a facilitator or barrier [9].

A key contribution of the ICF is to provide a framework and a structure for collecting and organizing clinical information evaluated by professionals worldwide, providing a universal language [9,11]. As such, the ICF is an important contribution to the growing interest in identifying children's needs based on their profiles of functioning rather than using only diagnostic labels, including ASD [13–15].

The practical application of the ICF-CY (from here we use 'ICF' to refer to both classifications) has been a challenge in clinical practice, including in clinical assessments of children with ASD, as the entire classification is comprehensive, consisting of 1685 ICF categories, In 2018, Bölte et al. following a rigorous step-wise multiple study methodology specified by the ICF Research Branch of the WHO Collaborating Centre for the Family of International Classifications in Switzerland, developed ICF Core Sets for ASD to facilitate its use [16]. ICF Core Sets represent shortlists of ICF categories that cover the most relevant areas of functioning and disability in a specific condition, which facilitate the application of the ICF in day-to-day practice. The Comprehensive Core Set for ASD consists of 111 categories and the common abbreviated set has 60 categories; the version for children 0–5 years of age has 73 categories, the version for children 6–16 years of age 81 categories, and the version for adults 79 categories [16,17].

Even though the ICF Core Sets for ASD, developed for the international context, highlight the most relevant categories for ASD out of the entire ICF classification, the length and complexity of these ICF Core Sets make them still difficult to use in everyday clinical encounters in Argentina.

There are multiple benefits of adopting ICF-based tools in clinical practice [15,18]. The systematic use of ICF-based tools defining the minimal key areas of functioning to be measured and reported for a given condition may be helpful to guide treatment planning, to identify facilitators and environmental barriers, and to reduce disparities in services. Moreover, ICF-based tools facilitate involvement of parents as active participants in the decision-making process on treatment goals and evaluation of intervention outcomes.

In Argentina, there is consensus on the diagnosis and treatment of people with ASD [19], but there are no guidelines that standardize the assessment of daily functioning in children with ASD. This highlights the need of a tool to systematically describe functioning of children with ASD in a comprehensive way. To fill this gap, the overall purpose of this study was to create a brief ICF-based tool to standardize assessments of ASD, with the following specific aims: (1) to identify the most relevant categories from the ICF Core Sets for ASD in order to describe the daily functioning of children with ASD in our country; (2) to propose measurement scales to evaluate each ICF category identified in aim 1; (3) to assess the feasibility of using a self-developed shortlist of ICF categories in clinical encounters; and finally (4) to describe the profile of the functioning of children with ASD at our national referral center.
