Blood Work for a 2-Year-Old Child with Autism
For a 2-year-old child with autism, order chromosomal microarray (CMA) and Fragile X testing as first-tier genetic tests, and consider a complete blood count, comprehensive metabolic panel, lead level, and thyroid function tests based on clinical indicators. 1, 2
First-Tier Genetic Testing (Essential)
The most recent AAP guidelines (2020) establish CMA and Fragile X analysis as the foundational genetic workup for all children with autism spectrum disorder 1. These tests should be discussed and offered regardless of whether intellectual disability is present, representing a shift from older 2000 guidelines that restricted testing to those with co-occurring ID 1.
For females specifically, consider MECP2 testing as part of the initial evaluation 1, 2. If family history suggests X-linked inheritance patterns, immediate referral to clinical genetics is warranted rather than attempting to navigate this independently 1.
Metabolic and Hematologic Screening (Selective, Not Routine)
When to Order Metabolic Tests
Do NOT order routine metabolic panels in the absence of specific clinical indicators 2. However, maintain high suspicion and order testing if you observe:
- True developmental regression (not just plateau)
- Seizures or movement disorders
- Failure to thrive
- Lethargy or poor physical endurance
- Acidosis on basic labs
- Extrapyramidal signs 2
If metabolic testing is indicated, include: complete blood count, comprehensive metabolic panel, serum amino acids, and urine organic acids 2.
Complete Blood Count Considerations
Recent research shows children with autism may have lower mean corpuscular volume (MCV) and higher lymphocyte counts compared to controls 3, 4. While these findings are not diagnostic, a CBC can identify:
- Anemia (which may warrant iron studies)
- Macrocytic changes suggesting B12/folate deficiency 4
- Baseline hematologic profile
Lead screening deserves special attention: 13% of children with autism in one UK study had elevated blood lead levels, and neither pica nor developmental delay reliably predicted which children had elevation 5. This supports routine lead screening in preschool autism populations 5.
Thyroid Function
While not explicitly mandated in the primary guidelines reviewed, thyroid screening is reasonable given the overlap between thyroid dysfunction and neurodevelopmental presentations. Include TSH at minimum.
What NOT to Order Routinely
Avoid ordering tests without clinical indication 6:
- EEG (unless seizures or regression present)
- MRI (unless microcephaly, focal neurologic signs, or significant regression) 2
- Extensive metabolic panels in asymptomatic children
- Inflammatory markers (TNF-α, IL-6) - these show group-level research differences but lack clinical diagnostic utility 7
A 2017 study found 76.8% of clinicians ordered at least one inappropriate test when evaluating autism, representing unnecessary cost and burden 6.
Second-Tier Testing
If first-tier genetic tests are unrevealing and no diagnosis is established, consider:
- Referral to clinical genetics for exome sequencing (ES) or whole genome sequencing 1
- PTEN testing if head circumference exceeds 2.5 standard deviations above mean 2
- Mitochondrial testing only if constitutional symptoms, hypotonia, repeated regressions after age 3, or multi-organ dysfunction present 2
Critical Pitfall
The most common error is failing to order recommended genetic tests: 10% of clinicians didn't order any genetic tests for autism with ID, and 40% didn't order them for autism without ID 6. Don't let this be you—CMA and Fragile X are evidence-based first-tier tests that should be offered to all families 1.