The aim of this research is to explore whether the number of new diagnoses of autism spectrum disorder (ASD) recorded in primary care records is changing, and describe any such changes.
Some studies suggest that diagnoses of autism in developed countries are increasing: recorded diagnoses of autism in the US rose from 2.2% in 2014 to 2.8% in 2016. The CPRD is the most accurate, complete and representative database available in which to study recording of ASD diagnoses in primary care.
We will use patient-level data to estimate trends in diagnosis rates over 20 years (1998 2018) in several ways.
First, by age group mirroring NICE guidelines for recognition and referral of autism in children and young people: pre-school (0 5 years), primary school (6 11 years), secondary school (12 19 years) with a group to capture the trend in adult diagnosis (over 19 years).
Second, by functional impairment, using the diagnoses of Aspergers syndrome and infantile autism as proxy measures for high functioning and severe autism respectively. This analysis will capture the influence of changes to diagnostic criteria from the publication of the DSM-5 in 2013.
Third, by gender: largely an exploratory study of time trends in recognition and recording in primary care broken down by gender.
Data will provide information on the number of recorded diagnoses of ASD in primary care and whether and how diagnosis is increasing over the different age groups to inform policy and planning of services for people with ASD and their families.
The objectives are to explore time trends in the diagnosis of ASD from 1998 to 2018. We are concerned not with absolute prevalence of autism, but of autism diagnosis as recorded in primary care itself. Our focus is on trends in recognition of autism, rather than on autism incidence and prevalence per se.
We will examine ASD using all relevant diagnostic codes (Appendix 1). This study will be largely descriptive, focussed on painting a picture of the current situation revealed by UK primary care data, rather than undertaking detailed comparative analysis or any attempt to define causal links.
Based on available evidence, we anticipate the number of people of any age receiving any ASD diagnosis will be increasing, year on year.
For separate developmental stages we have separate hypotheses:
1/ That the modal age of diagnosis in the pre-school age group (0 5 years) is dropping as awareness of early diagnosis of autism increases and diagnostic tools improve.
2/ That an increase in diagnosis in the adolescent (12 - 19 years) and adult groups will be largely driven by the increase in diagnoses of AS and HFA.
3/ In adults (over 19 years) a sharp rise is anticipated in previously undiagnosed Aspergers with a peak after the Autism Act (2009) required all local authorities to provide adult assessment for autism.
We will also explore the age-distribution of diagnoses to examine whether there are peaks in diagnosis for example at transition from nursery to primary school (age 4) and to secondary school (age 11). Here difficulties in adjusting to a new environment or new set of expectations will necessitate increased support precipitated by diagnosis.
We hypothesise that diagnoses of HFA will increase more than SA over the twenty years based on findings of a similar US study in 2002.
Percentage (%) of children, adolescents and adults with a new record of an autism diagnoses in each year (1998-2018).
Autism incidence will be obtained by dividing the number diagnosed as autistic by the number with acceptable data in the population. At each age-band (either preschool, child, adolescent or adult) incidence will be the number of patients with a new diagnosis divided by the total number of patients active in the study population in the age-band for that year, a method in common with Taylor et al. (2009).
Ginny Russell - Chief Investigator - University of Exeter
Sally Stapley - Corresponding Applicant - University of Exeter
Andrew Salmon - Collaborator - University of Exeter
Anita Pearson - Collaborator - NHS England
Tamsin Ford - Collaborator - University of Cambridge
Tamsin Newlove-Delgado - Collaborator - University of Exeter