This pilot clinical trial tests the hypothesis that certain blood metabolite levels can be used to predict Autism Spectrum Disorder (ASD). The study cohort will consist of 200 participants between the ages 18 and 60 months who have been referred to a developmental pediatric center for clinical evaluation of ASD or other developmental delay. Two selected sites will enroll 75 participants each with another 50 typically developing participants. Participants will receive a physical exam (including a dysmorphology evaluation), ADOS, VABS, MSEL, DSM-5, and M-CHAT assessments, and receive a diagnosis. A fasting blood draw is required, consisting of 2 mL vacutainer tubes (max 4 mL). Sites must process blood according to sponsor requirements (outlined in the Sponsor's Laboratory Manual). Certain metabolite levels in the blood will be used for diagnostic screening test development.

The primary objective is to conduct a double-blind, proof-of-concept, two-site, prospective study of 200 children aged 18-60 months that have been referred for an ASD evaluation by a physician to assess the feasibility of a blood test that measures a set of blood plasma metabolites and the classification algorithm developed thereof to predict the risk of ASD.

The secondary objective is to collect additional information for sub-classification of participant cohorts including Vineland Adaptive Behavior Scale (VABS) and Mullen Scale of Early Learning (MSEL) as well as any comorbidities that may correlate with blood test scores.

Inclusion Criteria:

In order to be eligible to participate in this study, an individual must meet all of the following criteria:

1. 18-60 months of age
2. Primary language is English (this is due to the evaluation instruments being used, which are in the English language).
3. Suspected developmental concern and referral to the developmental center by child's physician
4. Parental informed consent to participate in the study (based on the age range of the children in this study, assent is being waived)
5. Willingness to comply with all study procedures
6. Not currently enrolled in another clinical trial

Exclusion Criteria:

An individual who meets any of the following criteria will be excluded from participation in this study:

1. Previous diagnosis of ASD or DD
2. Prematurity < 34 weeks' gestation
3. Has a sibling already enrolled in the trial
4. Profound sensory deficits (e.g., hearing and vision deficits) that could interfere with the interpretation of study results
5. Documented current or active seizures, as defined by a clinical seizure or abnormal EEG within the past six months
6. Major genetic defect as determined by chromosomal microarray or other method of genetic detection
7. Currently taking any high dose (greater than recommended daily allowance) dietary supplements
8. Diagnosis or suspicion of recent viral/bacterial infection within 2 weeks of enrollment
9. Diagnosis with congenital brain malformations, moderate to severe traumatic brain injury, congenital or acquired microcephaly, or infection of the central nervous system (e.g., meningitis, viral encephalitis)
10. Fetal alcohol syndrome, Down syndrome, or another recognized syndrome
11. Usage of acetaminophen (e.g., Tylenol) within the past 72 hours
12. Fever (temperature > 100 degrees Fahrenheit) within the past 72 hours
13. Any other reason that the clinical investigator feels may place the participant at an unnecessary risk to participate

Up to 250 participants, ages 18-60 months suspected of ASD or a developmental delay who are referred for evaluation at participating pediatric developmental centers.