To date, no universal biological (e.g., genetic) or behavioral (e.g., response to name) marker for ASD has been identified that meets all standards of sensitivity, specificity, PPV, and NPV (Barton, Dumont-Mathieu, & Fein, 2012). Until a universal marker has been identified for ASD, a combination of surveillance and screening practices is recommended for detecting ASD in the general population. For children with ASD, parents often identify first concerns about language development within the first 2 years of life. Language delay, however, is not specific to ASD; early social-communicative behaviors consistently predict ASD diagnosis in young children. For example, an early indicator of ASD includes lack of social responsiveness (e.g., child does not respond when name is called). Indeed, early in development, many parents question whether their child may be deaf or have a hearing impairment. Other social-communicative behaviors predictive of ASD diagnosis early in development (i.e., by around 18 months) are lack of response to name, lack of protodeclarative pointing (i.e., pointing out objects for the purpose of sharing interest with others), no pretend play, and poor response to joint attention (e.g., following another’s gaze to an object or person of interest). Recommended ASD screeners are those that sample such social-communicative behaviors and play, such as the Modified Checklist for Autism in Toddlers-Revised (MCHAT-R/F; Robins, Fein, & Barton, 2009). The MCHAT-R/F is designed for use with 16–30-month-olds and recommended for ASD screening in primary care.

Chapter 5 of the present volume provides a review of various methods and strategies for screening for ASD using both Level I and Level II screeners. Several general points warrant inclusion in this chapter, however. First, ASD screeners may be incorporated in various service delivery settings, such as primary care and preschools. Second, despite repeated calls for screening within primary care settings, many pediatricians do not routinely screen for ASD according to the recommendations published by the AAP (e.g., Arunyanart et al., 2012). As such, ASD screening efforts will likely need to extend to nontraditional settings and be administered by individuals outside of the traditional parameters of healthcare, such as individuals working in daycare settings. Third, although the focus of this section of the chapter is on young children, older children who show age-appropriate language and cognitive development accompanied by mild ASD symptomatology may not come to clinical attention to service providers early in development. Therefore, surveillance and screening efforts are also appropriate for children in kindergarten and elementary school. Several measures exist for screening older individuals, such as the Social Responsiveness Scale, Second Edition (Constantino & Gruber, 2012). Although the field has yet to identify a universally appropriate screening measure, sound measures and methods exist to identify risk of ASD for younger and older children.

When concerns are raised in the surveillance and screening process, a comprehensive diagnostic evaluation should be conducted. A diagnosis of ASD is made based on the presence of certain behaviors and the absence of others. The new diagnostic criteria for ASD, as presented in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5; APA, 2013), requires that during the early developmental period, a child demonstrates impairments in social communication and interaction and restricted and repetitive patterns of behaviors. Examples of social communication deficits that may be present include difficulties in social-emotional reciprocity, impaired nonverbal communication skills, and difficulties building and maintaining relationships with others. Restricted and repetitive behaviors (RRBs) that may be observed in individuals who meet criteria for an ASD diagnosis include stereotyped repetitive movements, object use, or speech; rigidity; highly fixated interests; and over or under reaction to sensory input. Although these core symptoms are common behaviors among individuals diagnosed with ASD, as a spectrum disorder, the presentation of symptoms are diverse. Prognoses vary from one child to the next based on the severity of the symptoms displayed. The best indicators of prognosis include cognitive ability (e.g., IQ), joint attention skills by age 4, and functional spoken language by age 5 (Johnson & Myers, 2007).

It is widely accepted that early diagnosis of ASD is imperative given the considerable effect early intervention has on later outcomes. The behavioral symptoms characteristic of ASD appears during the early developmental period, typically before age 3 (APA, 2013). Research has indicated that the core impairments associated with ASD are present and identifiable during the second year of life (Pierce, Carter, Weinfield, & Desmond, 2011), if not sooner (Kozlowski et al., 2011). From an early age, children with ASD often exhibit developmental delays in orienting to social stimuli, play skills, motor imitation, and joint attention skills (McConnell, 2002; Stone et al., 2000; Webster et al., 2003; Woods & Wetherby, 2003). Most commonly, parents of children later diagnosed with ASD identified concerns with speech/language development, social responses, and medical concerns within the first 2 years of their child’s development (De Giacomo & Fombonne, 1998). A study by Kozlowski et al. (2011) found that delays in communication are not necessarily ASD specific, although parents of children later diagnosed with ASD noted these concerns significantly earlier in their child’s development than parents of children with non-ASD-related developmental delays. Further, there was a significant positive correlation between the age at which parents first noted communication delays and age of evaluation. Thus, parental knowledge of delayed developmental milestones related to communication resulted in their children receiving evaluations at younger ages.

In addition to the social and communication impairments associated with ASD, the importance of RRBs in facilitating early diagnosis has been emphasized as well. More specifically, Kim and Lord (2010) demonstrated diagnostic differences in the prevalence and severity of RRBs among young children with ASD, developmental delays, or typical development. Utilizing semi-structured observation methods to assess for RRBs and social and communication deficits has been shown to increase the likelihood of a stable ASD diagnosis over time (Kim & Lord, 2010).

The new diagnostic criteria for ASD provided within the DSM-5 differ significantly from the previous versions of the manual. Likely, the most significant change to DSM-5 is the elimination of the separate diagnostic categories for the subtypes of pervasive developmental disorders (e.g., autistic disorder, Rett’s disorder, childhood disintegrative disorder, Asperger’s disorder, and pervasive developmental disorder, not otherwise specified (including atypical autism)). Instead, within the neurodevelopmental disorders, the DSM-5 provides a single diagnostic category of ASD.

When comparing the DSM-5 diagnostic criteria for ASD to the DSM-IV-TR (APA, 2000) diagnostic criteria for autistic disorder, there is a notable change to the required age of onset for the disorder. Previously, a child had to display symptoms prior to age 3; DSM-5 requires symptoms be present in the early developmental period. Furthermore, the previous diagnostic criteria for autistic disorder included three domains (i.e., impaired social interaction, impaired communication, and restricted repetitive and stereotyped behaviors). DSM-5 reorganizes the social communication/interaction domain by combining the previous versions social interaction and communication domains and omitting the first DSM-IV-TR criteria for autistic disorder, which required a delay/absence of speech accompanied by failure to compensate. In DSM-5, a child’s failure to speak in itself no longer serves as a diagnostic criteria for ASD. In comparison with previous diagnostic criteria for Asperger’s disorder , the presence or absence of language delays no longer preclude diagnosis of ASD in any way. Although understanding the role of delayed or disordered language is important in the interpretation of an individual’s specific features of ASD, language delays in themselves are not included in the diagnostic criteria of ASD. Another new addition to the diagnosis of ASD is the inclusion of sensory symptoms in the list of illustrative examples provided for repetitive behaviors.

The DSM-5 also includes specifiers for associated features of ASD by individual. This provides information regarding other disorders that may also be present (e.g., intellectual impairment, language impairment) and allows for the diagnosis of ASD in individuals with genetic conditions (e.g., Rett syndrome, fragile X syndrome) or other neurodevelopmental, mental, or behavioral disorders. Thus, the clinician does not have to choose between a genetic descriptor or a behavioral diagnosis, but can apply both when appropriate.

The changes to the diagnostic criteria presented in DSM-5 are not without controversy. Initial research has demonstrated that the DSM-5 diagnostic criterion for ASD results in increased specificity when compared with DSM-IV-TR, which may reduce the number of children who are diagnosed as having ASD when they do not (Frazier et al., 2012). However, there has also been concern that the new criteria may significantly alter the population of individuals diagnosed with ASD moving forward. Research has demonstrated that individuals previously diagnosed with PDD-NOS and Asperger’s disorder are less likely to exceed the diagnostic threshold required to receive an ASD diagnosis per the DSM-5 criteria (McPartland, Reichow, & Volkmar, 2012). Other studies have demonstrated that the prevalence of ASD would decrease only to the extent that the majority of children who no longer meet the diagnostic criteria for ASD would meet criteria for social (pragmatic) communication disorder (SCD) , which is a new diagnosis in the DSM-5. A diagnosis of SCD is appropriate for those individuals who demonstrate deficits in the use of verbal and nonverbal communication for social purposes. A diagnosis of SCD differs from ASD in that a diagnosis of ASD requires symptoms related to social communication and the presence of restricted, repetitive patterns of behavior, interests, or activities. Before diagnosing SCD, ASD must first be ruled out.

Kim et al. (2014) compared clinical diagnoses made with DSM-IV-TR criteria for subtypes of autistic disorder, Asperger’s disorder, and pervasive developmental disorder not otherwise specified (PDD-NOS), to that of DSM-5 diagnostic criteria for ASD and SCD. Overall, results indicated that 83 % of the children who received a diagnosis of autistic disorder using DSM-IV criteria would still receive a diagnosis of ASD using the new DSM-5 criteria. Specific results by diagnostic subtype indicated that, of the children previously diagnosed with autistic disorder, 99 % met criteria for ASD and 1 % met criteria for SCD. Of the children previously diagnosed with Asperger’s disorder, 91 % met criteria for ASD, 6 % met criteria for SCD, and the other 3 % were diagnosed with a non-autism spectrum disorder. Regarding children previously diagnosed with PDD-NOS, 71 % met criteria for ASD, 22 % met criteria for SCD, and 7 % were diagnosed with another non-autism spectrum disorder. Thus, the large majority of children previously diagnosed with autistic disorder and Asperger’s disorder using the DSM-IV-TR autism subtypes would still be diagnosed with ASD using the DSM-5 criteria. Those children who previously had received a diagnosis of PDD-NOS are more likely to receive the new diagnosis of SCD, as these children may not demonstrate high levels of the core symptoms associated with ASD, or may demonstrate significant language deficits, but, few to no RRBs. Currently, there are no treatment recommendations for SCD. Kim et al. suggests that treatment for ASD and SCD should be the similar or the same until future research indicates otherwise.

Although, it is possible to reliably diagnose children with ASD as young as 24 months of age (Johnson & Myers, 2007), the CDC established Autism and Developmental Disabilities Monitoring (ADDM) Network reported a much later median age (i.e., 4 years, 5 months) for earliest ASD diagnosis. While a diagnosis of ASD may be clear for some, it may be more difficult for other individuals given the presentation of behaviors and/or presence of comorbid disorders. ASD is a spectrum disorder, and, as such, it is associated with a broad range of symptoms that can affect individuals to varying degrees in severity, with the presentation of symptoms potentially changing over time (Lord, Corsello, & Grzadzinski, 2014). Further, barriers that families face when seeking a diagnostic evaluation for ASD may include a lack of access to highly qualified professionals, increased levels of parental stress and anxiety, and financial barriers (Matson & Goldin, 2014).

The “gold standard” for a diagnostic evaluation of ASD involves the clinical judgment of a qualified interdisciplinary team to determine diagnosis, which includes utilizing empirically—sound diagnostic instruments, clinical assessment, caregiver report, and behavior observations. Although a diagnosis made by an interdisciplinary team is the ideal, this is not always feasible due to availability in a given location and extensive waitlists for such evaluations. Individuals with expertise in ASD can also conduct evaluations independently. The core features of an evidence-based assessment for ASD in children and adolescents include caregiver reporting on interviews and questionnaires, autism-specific diagnostic tools and observation instruments, standardized assessment of intellectual functioning, speech/language assessment, and adaptive behavior assessment (Ozonoff, Goodlin-Jones, & Solomon, 2005).

The use of accurate, reliable, and valid diagnostic instruments is an essential part of the assessment process to identify and diagnose ASD. ASD-specific assessment measures differ in the degree to which they emphasize the presence of observable behavioral abnormalities and lack of typical-developing features (Lord et al., 2014). When diagnosing an individual with ASD, quantifying the presentation of social communication and RRB symptoms is important to determine the level of severity and support they may benefit from in each of these respective areas. For instance, the DSM-5 allows practitioners to delineate between three levels of support (i.e., very substantial support, substantial support, or support) for social communication deficits and RRBs. These designations will hopefully aid in the identification of areas of relative strengths and weaknesses as they relate to ASD core symptomology and facilitate individualized intervention planning.

There are a variety of autism scales available that clinicians may utilize to aid in the assessment and diagnosis of ASD (Matson, Nebel-Schwalm, & Matson, 2007). A systematic review of accuracy, reliability, validity, and utility of diagnostic tools and assessments conducted by Falkmer, Anderson, Falkmer, and Horlin (2013) found the Childhood Autism Rating Scales, Second Edition (CARS-2; Schopler, Van Bourgondien, Wellman, & Love, 2010), Autism Diagnostic Interview-Revised (ADI-R; Le Couteur, Lord, & Rutter, 2003), and Autism Diagnostic Observation Schedule (ADOS; Lord, Rutter, DiLavore, & Risi, 2002) were the three instruments that had the strongest evidence base and highest levels of sensitivity and specificity when diagnosing autism. Although the CARS-2 was found to have the overall strongest correct classification for ASD diagnosis (0.86), it is a measure that is not administered in isolation. As the CARS-2 is a rating form completed by the clinician, clinical observations, caregiver reporting, and the child’s performance on other testing measures also inform ratings. Although an in-depth review of these diagnostic measures is beyond the scope of this chapter, a brief description of the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2; Lord et al., 2012) and the ADI-R (Le Couteur et al., 2003) is provided here.

Autism Diagnostic Observation Schedule, Second Edition (ADOS-2 : Lord et al., 2012). The ADOS-2 is a play-based assessment that incorporates standardized social interactions and activities that enable examiners to observe behaviors that are considered to be integral to the diagnosis of ASD. The ADOS-2 is a semi-structured standardized assessment that typically takes at least 45 min to administer. The ADOS-2 consists of five different modules; the module chosen is determined by development and language level of the child. This instrument should not be used in isolation, but does provide examiners the opportunity to elicit and directly observe behaviors typically associated with ASD. The ADOS-2 should be always used in conjunction with developmental history, caregiver report, other standardized testing, and clinical observation to determine a diagnosis of ASD.

Autism Diagnostic Interview–Revised (ADI-R ; Le Couteur et al., 2003). The ADI-R is a semi-structured interview for caregivers of children and adults. The interview focuses on behaviors that align with the three diagnostic domains of the DSM-IV-TR ASD diagnosis (e.g., quality of social interaction, language and communication, and restricted repetitive and stereotyped behaviors). The measure typically takes about 90 min or more to administer and includes 94 questions regarding the individual’s current functioning, with the exception of certain items that specify age restrictions for the assessed behavior. For example, questions that assess group play are coded for behavior displayed between the ages of 4 and 10 years; items that assess reciprocal friendships are scored for children who are ages 5 and older; and questions related to circumscribed interests are scored only for children ages 3 and above. In addition to asking about current behavior, each question focuses on the developmental time period between the ages of 4 and 5 years, when these behaviors were likely to be the most pronounced.

Falkmer et al. (2013) found that when the ADOS (Lord et al., 2002) and ADI-R (Le Couteur et al., 2003) were used in combination, they yielded the strongest accuracy in classification of ASD as compared to using the current “gold standard” team diagnosis approach. It should be noted that when used independently, the ADOS demonstrated stronger utility for an autistic disorder diagnosis than an ASD diagnosis, and the ADI-R provided more accurate classification for children older than 3 years old. Thus, during the assessment process, these instruments were more effective at identifying the presence of ASD in those children who were older than 3 years old and who presented with symptomology more indicative of DSM-IV-TR’s diagnostic subcategory of autistic disorder (APA, 2000), a category distinction that is no longer made given the diagnostic criteria in DSM-5.

Mazefsky, McPartland, Gastgeb, and Minshew (2013) conducted an analysis to determine how well an individual’s performance on the ADI-R and ADOS predicted a diagnosis of ASD using the DSM-5 criteria. The research sample consisted of a large number of research participants who were verbally fluent and considered to be “high functioning” on the autism spectrum (i.e., those who using the previous DSM-IV-TR criteria had received diagnoses of PDD-NOS or Asperger’s disorder). Within this population, results indicated that when using the ADOS alone, there were a disproportionately lower number of individuals who met diagnostic criteria versus using the ADI-R alone (33 % and 83 %, respectively). However, when the ADOS and ADI-R were used in combination, 93 % of the participants in this study met diagnostic criteria for an ASD diagnosis in all categories. These results indicate that for those individuals who demonstrate repetitive behaviors at lower rates of frequency/intensity, additional assessment measures will be required to capture the range of repetitive behaviors included in the DSM-5 criteria. Thus, Mazefsky et al. supported the use of both the ADOS and the ADI-R as part of the interdisciplinary team’s assessment process.