Introduction:

Autism or Autism spectrum disorder ( ASD) is a neurodevelopmental disorder that begin in the first 3 years of life and led to lifelong disability, specially to communications with people and world around these patients(1).Autism was first described in 1943 by Kanner(2) Patients withautismhave specialmedical,educational and socialneeds, andcorrectestimateof its prevalencein planningis important. Until the 1990s, autism estimationprevalencewas 4 to 5 persons per 10000 people, but recently prevalence ofall autism spectrum disorders increased(30-90cases per 10000). The causes of this increase includes: increase  number of true diagnose, changing diagnostic  criteria,  different  methods  of  ascertainment, and use of screening tests (3).

Studies have shown that autism is three to four times more common among boys than girls(Fombonne, 2005). Autism has various symptoms raised from neurobiological malfunction of brain, but three symptoms are more common in autistic persons and so used for diagnose autism. These symptoms are including: (1) difficulties in social interaction (nonverbal communication such as: lack of eye contact, facial expression and age-appropriate peer relationships),(2) restricted, repetitive or stereotyped behaviors and activities (inflexible adherence  to specific routines, pronounced preoccupation with one or more unusual and  restricted  interests) (3) Defects in language development and other  communication  skills (delays or lack of language acquisition, inability  to initiate or maintain a conversation and lack of age appropriate play). Nevertheless, non-specefic symptoms such as; abnormal sensory perception skills and experiences, motor awkwardness and insomniaThe complexityand diversity ofautismsymptoms, makedifficult toidentifythe causes it (6)

The etiology of autism is not well-known but studies revealed may be genetic susceptibility and environmental factors are involved. Genetic disorders include fragile X syndrome and tuberous sclerosis(1, 7). Environmental causes divided into pre-natal (e.g. congenital rubella  syndrome,  teratogen  exposure and pesticide exposure), peri-natal (e.g. associated with obstetric situations like low birth  weight,  abnormal  gestation  length  and  birth  asphyxia) and post-natal factors (e.g. autoimmune disease, gut  syndrome, viral  infection, amygdala developmental failure, oxidative stress, vitamin D deficiency, mercury toxicity and  the controversial  MMR  vaccine)(1,8-12) .

The DSM-IV-TR category of pervasive developmental  disorders  included  autistic  disorder, Rett’s  disorder,  Asperger’s  disorder,  childhood disintegrative  disorder,  and  pervasive  developmental  disorder  not  otherwise  specified  (PDD-NOS) (2).There is variability in the age at which children may present the features essential for this diagnosis. Its onset is before three years old. Despite the early onset of symptoms, oftendiagnose of thissyndromedoes not happenuntil severalyears later. Often Parents ofautistic children mention the child'ssymptoms  at 12-18monthsof age  but the diagnosisis usuallydelayeduntil4 years oldorlater (13).So,many childrenlosethe opportunityfor earlyintervention. Standardizedobservations, parentinterviews, and theevaluationbyprofessionals, are reliablediagnostic toolson theautismspectrum.Abig factorthat led to delay in diagnosis is professionalwhoperformsa preliminaryinvestigationwithout enough trainingand criteriafor diagnose ofautisticchildren. There aredifferent toolsforscreening anddiagnosis, buttheirdesign,strengths and weaknesses aredifferent. ADOS-G[1] is Gold standard in the diagnosis of autism. But it is expensive test and need long time andspecialists. Behavioral checklist that completed with parent are Often the only standard tools for screening (14) .Standardized screening test for general developmental problems recommended at the 9, 18 and 24 or 30 months old. Use of standard tools for screening in primary  care  surveillance is a effectiveness way to decline in complications caused bydelayed diagnosis (13-15).Today,there is considerable attentionto screening tools and various tools made for screening,thateach of them has its own advantagesand problems (16). Nevertheless, 22% of pediatricians use of these tools (17).

The screening tools must contain 4 characterizes:sensitivity, specificity,  positive predictive value (PPV), and negative predictive  value  (NPV). But most of researchersfocused on sensitivity and specificity.  Sensitivity and specificity of tools should be high. According to increased prevalenceof autism, health care providers have to focus on symptoms of autism andneed ability to detectearly diagnose to reduce theeffectsof delay intreatment(3).

To our knowledge any study is available aboutcomparing between advantages and weaknesses of different screening tools, soaim of this study was investigated these tools fromvarious aspects to provide a comprehensive view.

Search strategy:

Overthe past 15 years, there has been increasing documentation of the early signs of autism spectrum disordersthrough both individual retrospective parental reports and screening studies.

This study is a narrative literature review. Comprehensive searches of the scientific literature were conducted in 8 electronic databases(proquest,wiley,google scholar,SID,Scopus, Web of Science ،Science Direct ،Medline and prdiatric books.  language restriction was applied. The search strategy consisted of keywords and medical subject headings for autism and various screening tests. In addition, manual searches of the reference lists and searches of personal collections were conducted to identify additional citations.

Study selection:

The authors defined a search strategy to identify studies for inclusion. In addition, the inclusion criteria of the reviews must have addressed Screening tests which uses for identification the following ASD conditions: autistic disorder, Asperger syndrome, atypical autism, high-functioning autism, and suspected but not yet diagnosed autism.

The studies identified in the search were initially screened for relevance by one reviewer on the basis of their titles and abstracts, using broad criteria that were intended to be overly inclusive. Subsequently, two reviewers independently assessed the full text of potentially relevant studies and selected the studies using a standard form that outlined the eligibility criteria. Disagreements were resolved by consensus.

Results:

In this study, 28 screening tests were identifiedfrom 1992 to 2014. CHAT[2] is the Oldest test and the most recent test is CAST[3], which were built1992 and  2014. The maximum number of items were (113 items) in CBCL[4]screening test and the minimum number of test items were in  contrast  and  the rest of the interview and observation  .

According to these tests, the minimum age that can perform the screening is sixmonths that related to ITC. The highest age are RAADS-R[5] and AQ[6], that  theyare used for more than 18 years.

 Test duration was varied. Minimum time of 5 minutes for CHAT and the maximum time 90-120 minutes for ASIEP-3[7].

 In terms of sensitivity and specificity of the tests the highest sensitive is CASTtest with a sensitivity of 100% and the lowest  sensitive is M-ABC[8] test with a sensitivity of  41% .

The highest specificity is RAADS-R[9] test with a specificity 100% and the lowest specificity is ESAT test with a14%.The findings are summarized in Table 1.

Discussion:      

The purpose of this study was the evaluation and availability of the autism screening tests. The results show that none screening tools is not completely and better of  outhers.

In this study, 28 screening tests were identified. In study of Ghorbani et al,25 tests were reviewed of which 14 tests were related to screening and11tests were used for diagnosis (14).

In study of Meng-Chuan Lai, 13 screening tools find out and divided them into 3 sections including:

1)        Screening tools for  young children :Checklist for autism in toddlers (CHAT[10]) 18 month, Early screening of autistic traits (ESAT[11]) ,Modified checklist for autism in toddlers (M-CHAT[12]),Infant toddler checklist (ITC[13]) ,(Q-CHAT[14]),Screening tool for autism in children aged 2 years(STAT[15]).

2)         Screening tool for autism in older children and adolescents  : Social communication questionnaire (SCQ[16]) ,Socialresponsiveness scale, first or second edition (SRS, SRS-2),Childhood autism screening test (CAST),Autism spectrum screening questionnaire (ASSQ),Autism spectrum quotient (AQ).

3)        Screening: adultsAutism spectrum quotient (AQ), adult version,The Ritvo autism Asperger diagnostic scale-revised (RAADS-R) ( 18).

Handout in  his article about  screeining for autisem shows only 6 tools for autisem ,CHAT (Checklist for autism in toddlers),M CHAT(Modifi ed checklist for autism in toddlers), STAT(Screening tool for autism in children aged 2 years), CAST(Childhood autism screening test),PDDS_II(The Pervasive Developmental Disorders Screening Test-Second Edition),CSBS DP(Devalopmental Behavior Checklist-AutismScreening) ( 19).

In study of Marianne, only 8 screening scale for  young children find out which include (Checklist for autism in toddlers),M CHAT(Modifi ed checklist for autism in toddlers),  CHAT 23, ESAT (Early screening of autistic traits),PDDST-II ,FYI ,DBC-ES  and ITC(Infant toddler checklist)(15).

Study findings show that the majority of the questionnaires filled byparents . The reason is that parents have more information from children .This leads to faster and more accurate diagnosis. Early detection andintervention has an important role in reducing the negative effects of disorder.Based on these results, some tools for early and some are used for older ages.For example, the screening tool like CHAT used for ages 18-24 months(15).

CHAT was the first to be made(Baron-Cohen S 1992)(21). According to theBern study, after7 yearsfollow-up of 16235 children (mean age of 18/7months)reported that,94 case 0f ASD were identified. But CHAT reported only 33 children, which is a rate 2/03 per 1000. As a result, CHAT has a specificity of 97/7%, but a sensitivity of 35/1%and  a positive predictive value of 8/1%. Low sensitivity and high false-negative  rate indicate that the CHAT is not valid screening tool at 18 months(20).  Studies showed thatcombination screening tool such as  M- CHAT and interview reduce  false positivesand avoid parent concern (22) .

ITC is designed as a broadband screener for communication delays in6-12 months old children.It is designed to measure the following 7 language predictors that havebeen identified: Emotion, use of eye gaze, communication, gestures, sounds, words , understanding of words, and use of objects.

Wetherby et al (2003) compared validity of the ITC to standardized testing on 232 children between 12–24 months old and half with delay language and half with typical development.Sensitivity was 87.4% and specificity was 75.2% using the bottom 10^thpercentile or 1.25 standard deviations below average risk (22-23).

In study Of Wetherby et al (2008) that to examine the validity of  ITC in 5385 children  9-24 months  showed that,56 of 60 children that diagnosed with ASD , had positive test in ITC (23).

Results suggest that the ITC has high sensitivity and specificity (both 88.9%) for catching toddlers at risk for ASD and other developmental delays from a general pediatric sample. The ITC is a broadband screener, and therefore, a positive screen indicates that the child is at-risk for a communication delay but does not differentiate a child with ASD from a child with other developmental problems(23).

One of the most comprehensive screening tests  isESAT. It designed for 14-15 month old children, which has been studied in a population sample.The ESAT consists of fourteen parent report items, which include a variety ofplay skills, verbal and nonverbal communication, interest in others, emotional reaction, joint attention, social interaction, and eye contact (24). Distinction this test compared to other tests is broad domains are considers, as well as, it evaluate non –verbal aspects of autism.

The majority of the tests were attention to the main aspects of the communication disorder.Over time, the tests were more specialized than before.In specialized tests are attention to detail, imagination, pretend play and social interaction.for example, CAST is one of the new tools for autism screening.CAST is designed for children 4 to 11 years old. It is a parent questionnaire designed to screen for Asperger Syndrome and other social and communication disorders. The test consists of a 37-item yes/no parent questionnaire and cutoff at 15(25)

 Screening autism tools for older children are different from younger children .Tools for older children concentrate mainly on social communication.Total area of this test are including social behavior, peer relationships, imaginative play(26-27).  AQ test were designed toadult over 18 years, that attention to detail, imagination, communication(27).

Conclusion:

The results of this study indicate that any of the autism screening tools consider specific skill and various aspects of the disease, careful evaluation is need to choose proper test. No way is treat these patients via drug therapy. The only treatment is early detection through screening test. Early detection is the goal of the World Health Organization. Early diagnosis of autism before age 2 is a global challenge.