Validation of autism spectrum disorder diagnoses recorded in the Clinical Practice Research Datalink, 1990–2014

Figures & data

Table 1 Read codes indicating ASD

Read code	Read code description
ASDs
E140.00	Infantile autism
E140000	Active infantile autism
E140100	Residual infantile autism
E140.12	Autism**
E140.13	Childhood autism
E140000	Active infantile autism
E140z00	Infantile autism NOS
Eu84000	[X]Childhood autism
Eu84011	[X]Autistic disorder**
Eu84012	[X]Infantile autism
Eu84100	[X]Atypical autism
Eu84z11	[X]Autistic spectrum disorder
Asperger’s syndrome
Eu84500	[X]Asperger’s syndrome**
Pervasive developmental disorder
Eu84.00	[X]Pervasive developmental disorders
Eu84y00	[X]Other pervasive developmental disorders
Eu84z00	[X]Pervasive developmental disorder; unspecified

Notes:

** Indicates Read codes most commonly used by GPs to indicate ASD in the CPRD.

Abbreviations: ASD, autism spectrum disorder; CPRD, Clinical Practice Research Datalink; GP, general practitioner; ICD, International Classification of Diseases; NOS, not otherwise specified.

Table 2 Characteristics of ASD cases, overall and by sex

Characteristics	All ASD cases N=2154 (%)	Male ASD cases N=1810 (%)	Female ASD cases N=344 (%)
Child sex
Male	1810 (84.0)	–	–
Female	344 (16.0)	–	–
Year of first ASD diagnosis
<1995	3 (0.1)	2 (0.1)	1 (0.3)
1995–1999	55 (2.6)	50 (2.8)	5 (1.5)
2000–2004	254 (11.8)	208 (11.5)	46 (13.5)
2005–2009	657 (30.5)	568 (31.4)	89 (25.9)
2010–2014	1185 (55.0)	982 (54.3)	203 (59.0)
Age at ASD diagnosis (years)
<2.0	22 (1.0)	18 (1.0)	4 (1.2)
2.0–2.9	198 (9.2)	160 (8.8)	38 (11.1)
3.0–3.9	373 (17.3)	311 (17.2)	62 (18.0)
4.0–4.9	310 (14.4)	267 (14.8)	43 (12.5)
5.0–5.9	223 (10.4)	193 (10.7)	30 (8.7)
6.0–6.9	197 (9.2)	172 (9.5)	25 (7.3)
7.0–7.9	165 (7.7)	136 (7.5)	29 (8.4)
8.0–8.9	159 (7.4)	136 (7.5)	23 (6.7)
9.0–9.9	119 (5.5)	101 (5.6)	18 (5.2)
10.0–10.9	122 (5.7)	97 (5.4)	25 (7.3)
11.0–11.9	84 (3.9)	68 (3.8)	16 (4.7)
12.0–12.9	60 (2.8)	51 (2.8)	9 (2.6)
13.0–13.9	38 (1.8)	31 (1.7)	7 (2.0)
14.0–14.9	36 (1.7)	31 (1.7)	5 (1.5)
≥15.0	48 (2.2)	38 (2.1)	10 (2.9)
Number of ASD diagnoses
1	1688 (78.4)	1413 (78.1)	275 (79.9)
2	312 (14.5)	267 (14.8)	45 (13.1)
3+	154 (7.2)	130 (7.2)	24 (7.0)
ASD code
Autism spectrum disorder	1708 (79.3)	1440 (79.6)	268 (77.9)
Asperger’s	433 (20.1)	362 (20.0)	71 (20.6)
PDD	13 (0.6)	8 (0.4)	5 (1.5)
Supporting clinical codes
Core ASD signs
Behavioral problem	662 (30.7)	567 (31.3)	95 (27.6)
Developmental delay	259 (12.0)	206 (11.4)	53 (15.4)
Speech delay	431 (20.0)	365 (20.2)	66 (19.2)
Number of core signs
0	1062 (49.3)	889 (49.1)	173 (50.3)
1	859 (40.0)	729 (40.3)	130 (37.8)
2	206 (9.6)	167 (9.2)	39 (11.3)
3	27 (1.3)	25 (1.4)	2 (0.6)
Therapy	220 (10.2)	190 (10.5)	30 (8.7)
Specialist referral or visit	553 (24.7)	439 (24.3)	94 (27.3)
Letter from specialist on ASD diagnosis date	366 (17.0)	317 (17.5)	49 (14.2)
Suspected autism	41 (1.9)	38 (2.1)	3 (0.9)
Other characteristics
Repetitive movement	23 (1.1)	18 (1.0)	5 (1.5)
Gait abnormality	270 (12.5)	226 (12.5)	44 (1.8)
Parental concern	235 (10.9)	196 (10.8)	39 (11.3)
School problem	45 (2.1)	37 (2.0)	8 (2.3)
Sleep problem	329 (15.3)	271 (15.0)	58 (16.9)
ADHD	242 (11.2)	212 (11.7)	30 (8.7)
ADHD prescription	202 (9.4)	181 (10.0)	21 (6.1)
Epilepsy	96 (4.5)	79 (4.4)	17 (4.9)
Birth order
First	1092 (50.7)	928 (51.3)	164 (47.7)
Second	651 (30.2)	542 (29.9)	109 (31.7)
Third or more	277 (12.9)	233 (12.9)	44 (12.8)
Unknown	134 (6.2)	107 (5.9)	27 (7.9)

Abbreviations: ADHD, attention deficit hyperactivity disorder; ASD, autism spectrum disorder; PDD, pervasive developmental disorder.

Figure 1 General practitioner recorded ASD diagnosis subtype by birth year.

Abbreviations: ASD, autism spectrum disorder; DSM-IV, Diagnostic and Statistical Manual of Mental Disorders Fourth Edition; DSM-5, Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition.

Table 3 Characteristics of ASD cases, by birth cohort

Characteristics	Born in 1990–1999 N=562 (%)	Born in 2000–2004 N=831 (%)	Born in 2005–2009 N=660 (%)	Born in 2010–2011 N=101 (%)
Child sex
Male	471 (83.8)	716 (86.2)	537 (81.4)	86 (85.1)
Female	91 (16.2)	115 (13.8)	123 (18.6)	15 (14.9)
Year of first ASD diagnosis
<1995	3 (0.5)	n/a	n/a	n/a
1995–1999	55 (9.8)	n/a	n/a	n/a
2000–2004	192 (34.2)	62 (7.5)	n/a	n/a
2005–2009	191 (34.0)	378 (45.5)	88 (13.3)	n/a
2010–2014	121 (21.5)	391 (47.1)	572 (86.7)	101 (100)
Age at ASD diagnosis (years)
<2.0	7 (1.3)	7 (0.8)	6 (0.9)	2 (2.0)
2.0–2.9	37 (6.6)	50 (6.0)	77 (11.7)	34 (33.7)
3.0–3.9	50 (8.9)	114 (13.7)	158 (23.9)	51 (50.5)
4.0–4.9	46 (8.2)	95 (11.4)	155 (23.5)	14 (13.9)
5.0–5.9	32 (5.7)	93 (11.2)	98 (14.9)	n/a
6.0–6.9	41 (7.3)	83 (10.0)	73 (11.1)	n/a
7.0–7.9	37 (6.6)	69 (8.3)	59 (8.9)	n/a
8.0–8.9	43 (7.7)	91 (11.0)	25 (3.8)	n/a
9.0–9.9	41 (7.3)	69 (8.3)	9 (1.4)	n/a
10.0–10.9	38 (6.8)	84 (10.1)	n/a	n/a
11.0–11.9	46 (8.2)	38 (4.6)	n/a	n/a
12.0–12.9	34 (6.1)	26 (3.1)	n/a	n/a
13.0–13.9	29 (5.2)	9 (1.1)	n/a	n/a
14.0–14.9	33 (5.9)	3 (0.4)	n/a	n/a
≥15.0	48 (8.5)	n/a	n/a	n/a
Number of ASD diagnoses
1	387 (68.9)	653 (78.6)	554 (83.9)	94 (93.1)
2	109 (19.4)	120 (14.4)	77 (11.7)	6 (5.9)
3+	66 (11.7)	58 (7.0)	29 (4.4)	1 (1.0)
ASD code
Autism spectrum disorder	364 (64.8)	653 (78.6)	592 (89.7)	99 (98.0)
Asperger’s	193 (34.3)	173 (20.8)	65 (9.9)	2 (2.0)
PDD	5 (0.9)	5 (0.6)	3 (0.5)	0 (0.0)
Supporting clinical codes
Core ASD signs
Behavioral problem	222 (39.5)	278 (33.5)	149 (22.6)	13 (12.9)
Developmental delay	74 (13.2)	87 (10.5)	86 (13.0)	12 (11.9)
Speech delay	96 (17.1)	166 (20.0)	142 (21.5)	27 (26.7)
Number of core signs
0	251 (44.7)	404 (48.6)	352 (53.3)	55 (54.4)
1	239 (42.5)	335 (40.3)	244 (37.0)	41 (40.6)
2	63 (11.2)	80 (9.6)	59 (8.9)	4 (4.0)
3	9 (1.6)	12 (1.4)	5 (0.8)	1 (1.0)
Therapy	84 (15.0)	72 (8.7)	58 (8.8)	6 (5.9)
Specialist referral or visit	119 (21.2)	202 (24.3)	182 (27.6)	30 (29.7)
Letter from specialist on ASD diagnosis date	56 (10.0)	154 (18.5)	140 (21.2)	16 (15.8)
Suspected autism	3 (0.5)	19 (2.3)	16 (2.4)	3 (3.0)
Other characteristics
Repetitive movement	9 (1.6)	13 (1.6)	1 (0.2)	0 (0.0)
Gait abnormality	99 (17.6)	119 (14.3)	49 (7.4)	3 (3.0)
Parental concern	37 (6.6)	90 (10.8)	96 (14.6)	12 (11.9)
School problem	26 (4.6)	15 (1.8)	4 (0.6)	0 (0.0)
Sleep problem	107 (19.0)	130 (15.6)	79 (12.0)	13 (12.9)
ADHD	91 (16.2)	108 (13.0)	43 (6.5)	0 (0.0)
ADHD prescription	84 (15.0)	83 (10.0)	35 (5.3)	0 (0.0)
Epilepsy	48 (8.5)	26 (3.1)	19 (2.9)	3 (3.0)
Birth order
First	299 (53.2)	401 (48.3)	337 (51.1)	55 (54.5)
Second	162 (29.0)	258 (31.1)	203 (30.8)	27 (26.7)
Third or more	64 (11.4)	113 (13.6)	88 (13.3)	13 (12.9)
Unknown	37 (6.6)	59 (7.1)	32 (4.9)	6 (5.9)

Abbreviations: ADHD, attention deficit hyperactivity disorder; ASD, autism spectrum disorder; n/a, not applicable; PDD, pervasive developmental disorder.