There were 1392 children in the sample who had a documented autism spectrum disorder (ASD) diagnosis and documented age of first ASD diagnosis noted in surveillance records and included in analyses. A majority of the sample was male (84%), and the racial and ethnic distribution of the sample was 59% non-Hispanic white, 24% non-Hispanic black, 8% Hispanic, 3% non-Hispanic Asian or Pacific Islander, and 6% other or missing race. A total of 1090 children had cognitive test data available to assess whether the child had co-occurring intellectual disability (ID) and 45% had ID. Most of the 1392 children with a documented age of first ASD diagnosis met the surveillance definition for ASD (95%).

Of the 1392 children in the sample, 59% were first diagnosed with autism, 40% were first diagnosed with another ASD, and 1% did not have a first ASD subtype noted. The mean age at first reported ASD diagnosis was 57 months (range, 12–106 mo). Children with a first known diagnosis of autism were, on average, diagnosed earlier than children with a first diagnosis of another ASD (52 vs 64 mo, respectively, p < .01). The types of community professionals who recorded the first known ASD diagnosis were PhD psychologists (23%), MD developmental pediatricians (22%), professional not stated (19%), other health professional (11%, such as master’s level psychologists and speech/language pathologists), MD neurologists (9%), EDD or EDS educators (7%), MD other (6%), and PhD other (3%, most of the professionals in this category did not have a specialty stated). The types of community professionals who ruled out an ASD diagnosis after one had been recorded in education or health records were MD developmental pediatricians (31%), PhD psychologists (28%), EDD or EDS educators (10%), PhD other (10%), other health professional (6%), MD other (7%), professional not stated (5%), and MD neurologists (3%).

There were 61 children who had a change in ASD classification from ASD to non-ASD (4% of the sample). The mean age at first reported ASD diagnosis for children who later had an ASD excluded was 49 months (range, 18–95 mo) and the mean age when this ASD diagnosis was excluded was 69 months (range, 25–97 mo). The mean time between an ASD diagnosis and an ASD exclusion was 19 months (range, 1–69 mo); 14 children had a change in classification less than 6 months from first ASD diagnosis and 47 children had a change in classification 6 months or more from first ASD diagnosis. The percent of children with a change in classification from ASD to non-ASD would decrease from 4% to 3% if the 14 children with a change in classification less than 6 months from first ASD diagnosis were excluded. The most common diagnoses given at the time an ASD was excluded were language delay or disorder (39%), other specific developmental delay (adaptive, cognitive, motor, or social; 20%), and attention-deficit hyperactivity disorder (ADHD; 20%); 59 of the 61 (97%) children who had a change in ASD classification from ASD to non-ASD had at least 1 alternative diagnosis recorded when an ASD was excluded. Fifty children who had an ASD excluded after diagnosed were being served in a public school special education classroom at 8 years of age. The special education eligibility categories for these 50 children were autism (30%), learning disability (16%), speech/language impairment (16%), ID (12%), other health impairment (10%), emotional disturbance (8%), orthopedic impairment (4%), and developmental delay (4%).

There were several child factors that influenced whether a child had a change in classification from ASD to non-ASD (Table 1). We present data on only those developmental conditions that were commonly diagnosed when an ASD was excluded (noted above); the presence of these conditions indicates that a diagnosis was reported in education and/or health records (Table 1). There were no significant differences in proportions of children who had a change in ASD classification and those who did not have a change in ASD classification on child race, child sex, or ASD subtype noted at first documented ASD diagnosis. Children were more likely to have a change in classification from ASD to non-ASD if they were first identified as having an ASD at 30 months or younger; did not experience a developmental regression (or loss of previously acquired skills); or had ADHD, language delay or disorder; or other specific developmental delay diagnosed in evaluation records. Only 11% of children in the sample were first diagnosed with ASD at 30 months or younger. Children were also more likely to have a change in ASD classification from ASD to non-ASD if they were being served in a public school special education classroom other than autism at 8 years of age.

There were also several surveillance factors that influenced whether a child had a change in classification from ASD to non-ASD (Table 2). Record source (i.e., education only, health only, or both education and health) and type of professional who noted the first documented ASD diagnosis did not influence whether a child had a change in ASD classification from ASD to non-ASD. However, all other surveillance variables significantly influenced changes in ASD classification (i.e., final surveillance definition [i.e., whether the child met ASD surveillance criteria], number of records reviewed, surveillance site, and surveillance year [SY]).

Child and surveillance factors were then entered into a multivariable logistic regression model to determine factors most strongly associated with change in ASD classification from ASD to non-ASD when all factors were considered simultaneously. The presence of language delay or disorder and other specific developmental delays were combined into 1 variable (i.e., presence of language or other specific delays) due to the significant correlation between these variables (r = .12–.42, p < .01). Results indicated that identification of a language or other specific delay, presence of developmental regression, professional who noted first documented ASD diagnosis, timing of first documented ASD diagnosis, and type of special education classroom at 8 years of age were associated with whether a child had a change in ASD classification from ASD to non-ASD. Specifically, children who had a language or other specific delay or ASD onset not characterized by developmental regression were more likely to have an ASD excluded after diagnosed than children who did not have a language or other specific delay or ASD onset characterized by development regression. Children first diagnosed by a professional with a PhD, but no specialty stated or no degree or specialty stated, were also more likely to have a change in classification from ASD to non-ASD than children first diagnosed by other professionals. Children served (at the time of record review) in a special education classroom with an eligibility designation other than autism (such as ID or learning disability) were also more likely to have a change in classification from ASD to non-ASD. Finally, having a first ASD diagnosis at 30 months or younger was strongly associated with subsequent change in ASD classification from ASD to non-ASD (Table 3). These results were similar when children who had a change in classification less than 6 months from the first ASD diagnosis (n = 14) were excluded from regression analyses.

To our knowledge, this is the first population-based study of factors associated with change in classification from autism spectrum disorder (ASD) to non-ASD. We found that most children diagnosed before 8 years retain an ASD diagnosis at 8 years based on documented education and health records. ASD classification changed from ASD to non-ASD for only 4% of children in our sample (or 3% when children who had a change in ASD classification less than 6 months from initial ASD diagnosis were excluded). Our sample was unique because children were ascertained for ASD surveillance using population-based record-review surveillance instead of direct screening or clinical referral and changes in diagnosis from ASD to non-ASD were clearly documented in education or health records. Thus, our findings reflect documented community practices and indicate that young children diagnosed with an ASD in educational or health settings are likely to still meet criteria for an ASD when evaluated several years later,^9,10,12 which underscores the need for continued services. Although we could not assess symptom improvement in our study, some longitudinal analyses show that ASD symptoms may improve with age and intervention despite diagnostic retention.^8,19

Our findings differ from reports suggesting that up to 20% to 30% of children will have a change in classification from ASD to non-ASD.^13–15 However, key differences between ours and these other studies are methodology and timing of first ASD diagnosis. Children in our study were identified from population-based surveillance methods and diagnosed on average at 57 months, whereas children in some other studies were identified from direct screening and/or clinical referral in the toddler years.^13,14 Therefore, the earlier an ASD diagnosis is noted, the more likely a child may experience change in classification from ASD to non-ASD. In fact, we found that children diagnosed with an ASD at 30 months or younger were more likely to have a change in ASD classification from ASD to non-ASD than children diagnosed with an ASD at 31 months or older. These results might indicate that children identified earlier are more apt to respond to interventions during a key period of development. Likewise, children identified later may present with more diagnostic clarity; thus, overdiagnosis at younger ages cannot be ruled out. Overdiagnosis may be especially relevant for those children who received a change in classification from ASD to non-ASD less than 6 months from their first ASD diagnosis (n = 14, for children in our sample); however, exclusion of these children did not change results of multivariate analyses that show earlier diagnosis is associated with greater probability of change from ASD to non-ASD.

Other factors associated with change in ASD classification in our study were onset other than developmental regression, presence of language or other specific delays, and participation in a special needs classroom other than autism at 8 years of age. It has been reported that children who have an ASD and experience loss of skills have more cognitive and general impairment than children who have an ASD and do not experience loss of skills.^20,21 Thus, children who were not reported to have developmental regression (who may have less impairment than children who were reported to have developmental regression) may be more responsive to early intervention efforts or present with less diagnostic clarity in early childhood. Interestingly, children who had a language or other specific developmental delay were more likely to move from ASD to non-ASD than children who did not have another specific delay noted in evaluation records. This particular finding could imply difficulty with differential diagnosis between ASDs and language or other specific developmental delays in young children and need for more professional training on signs and symptoms that distinguish children with an ASD from children with other developmental concerns.

Children who had a first ASD diagnosis recorded by a professional with a PhD but no specialty stated or a professional who did not have a degree or specialty stated were more likely to change classification from ASD to non-ASD. However, the confidence intervals surrounding these estimates were wide, reflecting a great deal of uncertainty in the estimates. We did not have additional information in our dataset to further explore characteristics of these professionals, although professionals with no degree or specialty stated likely constitute a diverse group of professionals (e.g., nurses, occupational therapists, and physical therapists). Moreover, although child race only approached statistical significance in our final multivariable model, non-Hispanic black or African-American children were less likely to move from ASD to non-ASD than non-Hispanic white children. Other studies have found that non-Hispanic black children with ASD are, on average, identified later than non-Hispanic white children with ASD.²² If timing of first ASD diagnosis is one of the most important predictors of changes in ASD classification, as we report, and if that change is based at least partly on a lessoning of symptomatology in response to early intervention, then these data underscore the need to reduce racial disparities in ASD identification.

We did not find that subtype of first recorded ASD diagnosis predicted change in ASD classification. This finding contradicts other studies that suggest ASD diagnoses are less stable over time if the child was first diagnosed with pervasive developmental disorder—not otherwise specified (PDD-NOS) rather than autistic disorder.^12,16 Our subtype data could only be categorized into autism, other ASD, and ASD subtype not stated because some children had a 299.8 billing code, which applies to both PDD-NOS and Asperger’s disorder. Nonetheless, this particular finding suggests that autism spectrum diagnoses are more stable than subtype diagnoses, possibly because the subtype of PDD-NOS includes a broad range of symptoms and functional impairments. Consequently, ASD subtype may be a poor predictor of diagnostic trajectory and treatment response. Although children with ASD without an intellectual disability (ID) have shown greater symptom improvement than those with an ID,¹⁹ we did not find that the presence or absence of ID predicted a change in ASD classification from ASD to non-ASD in our sample. These results indicate that variables such as timing of first documented ASD diagnosis may be associated more with change in ASD classification than the presence of ID when considered simultaneously.

There are a few limitations to our analysis that warrant discussion. First, change in ASD classification from ASD to non-ASD was defined by information contained in education and health records rather than direct assessment of the child (although previous analyses suggest that most children who meet our ASD surveillance definition also meet clinical criteria for the disorders³). Change in ASD classification less than 6 months from first ASD diagnosis could represent overdiagnosis rather than improvement in ASD symptoms. However, factors that influence change in ASD classification did not change when children who had an ASD excluded within 6 months of diagnosis were removed from the multivariate analysis. Furthermore, change in classification from ASD to non-ASD was defined by the earliest documented ASD diagnosis found in surveillance records, although a child could have been diagnosed with an ASD before this first recorded date. Nonetheless, information contained in surveillance records reflects community perceptions of ASDs according to the professional who conducted an evaluation of the child, which is useful for assessment of variations in clinical practice.

There could be many reasons why a child has a change in classification from ASD to non-ASD, including possible overdiagnosis and improvement due to participation in early intervention programs. Consequently, one other consideration in interpreting these data is whether participation in early intervention programs in the surveillance sites examined differs from national averages, which could affect whether these results can be generalized to other states. However, early intervention participation in our 4 sites in 2006 was generally comparable to the national average (i.e., 2.33% of the total population in our 4 states compared with the 2.41% national average). We therefore conclude that early intervention participation rates in the surveillance sites examined were comparable to national averages and not indicated as a confounding factor in our analyses.

Another consideration is that 1 previous study found that the surveillance system had moderate sensitivity, indicating some children with ASDs were not identified by Autism and Developmental Disabilities Monitoring (ADDM) record-review methods.³ However, 11 of the 12 children with ASD who were not detected by ADDM methods in this study did not have an ASD diagnosis recorded in surveillance records.³ Thus, the less than ideal sensitivity reported in this study could represent difficulty detecting children without a clear presentation of symptoms that warrant an ASD diagnosis, and all children in our study had an ASD diagnosis noted in service records. Furthermore, ADDM surveillance identifies service records available from birth to 8 years of age and symptoms of high-functioning autism or Asperger’s disorder which may not be recognized in some children until later in childhood, or even later in life. Therefore, the proportion of children who experience a change in classification form ASD to non-ASD may be higher in samples that include children older than 8 years.

Although we could not assess the type or amount of intervention the child received since this information is not collected for ASD surveillance, we found the mean time between first diagnosis and exclusion of an ASD was 20 months. It is important to note the mean time between first ASD diagnosis and exclusion of an ASD also relied on age of first documented ASD diagnosis (and may be longer if the child received an ASD diagnosis before this time). Future analyses should consider type of treatment, length of treatment (from first ASD diagnosis and beyond 8 years of age), and number of treatment hours and how these variables interact with timing of first ASD diagnosis to influence change in ASD classification from ASD to non-ASD.

Despite these limitations, our results support past research that suggests children with ASDs are likely to retain their ASD diagnosis up to 8 years of age, which indicates the need for continued support and treatment for children with ASDs and their families. Up to 4% of children with ASDs may experience a change in diagnostic classification from ASD to non-ASD as they move through the course of childhood. Although we cannot determine the underlying reason for the change in diagnosis from ASD to non-ASD, our findings might indicate some children may be overdiagnosed whereas other children may experience a positive change in symptomatology, particularly those children who have an onset other than developmental regression, language or other specific developmental delays and are identified at 30 months or younger. Nonetheless, only 11% of children in our sample were first diagnosed with an ASD at 30 months or younger (Table 1). Furthermore, children were diagnosed with a wide array of co-occurring developmental delays and conditions other than ASDs. Given the small percent of children with ASDs identified early and the developmental concerns noted by other diagnoses, these data support the American Association of Pediatrics’ recommendations for early identification of symptoms of ASDs and developmental delays to help ensure children reach their maximum potential.^23,24