Should a child with autism spectrum disorder receive a trial of oral folinic acid (leucovorin), and what are the recommended screening tests (folate‑receptor‑alpha autoantibodies, CSF folate), dosing (2 mg/kg/day up to 50 mg), and trial duration (12–24 weeks)?

Leucovorin for Autism Spectrum Disorder

Direct Recommendation

Children with autism spectrum disorder should receive a trial of oral folinic acid (leucovorin) at 2 mg/kg/day (maximum 50 mg/day) for 12-24 weeks, particularly if they test positive for folate receptor alpha autoantibodies (FRAAs), as this treatment has demonstrated significant improvements in core ASD symptoms and behavioral problems in randomized controlled trials. 1

Evidence Supporting Leucovorin Treatment

Strongest Recent Evidence

The most recent and highest-quality evidence comes from a 2024 double-blind, placebo-controlled RCT that demonstrated:

• Significantly greater improvement in CARS scores with folinic acid (3.6 ± 0.8) compared to placebo (2.4 ± 0.7, p < 0.001) 1
• Superior behavioral outcomes with greater reductions in CBCL total scores (19.7 ± 9.5 vs. 12.6 ± 8.4, p < 0.001) and CBCL internalizing scores (15.4 ± 7.8 vs. 8.5 ± 5.7, p < 0.001) 1
• No adverse reactions reported in either treatment or placebo groups 1
• Enhanced response in FRAA-positive children, with more pronounced improvement in those with high-titer autoantibodies (p = 0.03) 1

Supporting Evidence Base

Additional research confirms these findings:

• A 2024 retrospective analysis of 110 ASD patients found that higher binding FRAA titers were associated with greater treatment response, with improvements in most SRS subscales and ABC irritability 2
• A 2013 study identified FRAAs in 75.3% of children with ASD, with treated children showing significantly higher improvement in verbal communication, receptive and expressive language, attention, and stereotypical behavior compared to wait-list controls over 4 months 3
• Approximately one-third of FRAA-positive treated children demonstrated moderate to much improvement 3

Recommended Screening Protocol

Biomarker Testing

Test for folate receptor alpha autoantibodies (FRAAs) before initiating treatment:

• FRAAs are present in 58-76% of children with ASD 4
• High-titer FRAAs predict better treatment response 1
• Blood FRAA titers correlate with cerebrospinal fluid folate levels 4
• Consider testing for soluble folate binding proteins (sFBPs), which are associated with severe ASD and medical complexity 5

CSF Folate Testing

CSF folate measurement is not routinely necessary for treatment decisions, as:

• Serum FRAA levels correlate with CSF 5-methyltetrahydrofolate concentrations 3
• CSF folate levels were below normative mean in all FRAA-positive cases tested 3
• The invasive nature of lumbar puncture makes it impractical for routine screening when serum biomarkers are available

Treatment Protocol

Dosing Regimen

Administer oral leucovorin calcium at 2 mg/kg/day with a maximum dose of 50 mg/day 3, 1

• This dosing has been validated across multiple studies 3, 4, 1
• The reduced folate bypasses the blockage at folate receptor alpha by using the reduced folate carrier, an alternate pathway 4

Trial Duration

Conduct a 12-24 week trial:

• The 2024 RCT demonstrated significant benefits at 24 weeks 1
• Earlier studies showed improvements over a mean period of 4 months 3
• Response assessment should occur at regular intervals throughout the trial period

Expected Outcomes

Improvements may be observed in:

• Core ASD symptoms (social communication, repetitive behaviors) 1
• Verbal communication and receptive/expressive language 3
• Attention and stereotypical behavior 3
• Behavioral problems including irritability 2, 1
• Internalizing symptoms 1

Clinical Algorithm

Step 1: Screen child with ASD for FRAAs and sFBPs 2, 5

Step 2: If FRAA-positive (especially high-titer) or sFBP-positive, initiate leucovorin trial at 2 mg/kg/day (max 50 mg/day) 3, 1

Step 3: Continue standard behavioral interventions (ABA, sensory integration therapy) concurrently 1

Step 4: Assess response at 12 weeks using standardized measures (CARS, SRS, ABC, CBCL) 2, 3, 1

Step 5: If showing improvement, continue to 24 weeks for full trial 1

Step 6: If no improvement by 12-16 weeks in FRAA-negative children, consider discontinuation 3

Important Caveats

Safety Profile

• The incidence of adverse effects is low across all studies 3, 1
• No adverse reactions were reported in the most recent RCT 1
• Treatment is well-tolerated even in medically complex patients 5

Treatment Context

Leucovorin should complement, not replace, evidence-based behavioral interventions:

• Standard care includes behavioral interventions based on applied behavior analysis principles 6
• The 2024 RCT administered folinic acid as add-on therapy to ABA and sensory integration therapy 1
• Do not delay or substitute evidence-based behavioral interventions for leucovorin treatment

Biomarker Considerations

• While FRAA-positive children show more pronounced benefits, FRAA-negative children may still respond 1
• sFBP-positive patients tend to have severe ASD and medical complexity but also respond to treatment 5
• The absence of biomarkers does not absolutely contraindicate a trial, given the excellent safety profile

Guideline Context

Note that the 2014 AACAP practice parameters do not specifically address leucovorin treatment, as the strongest evidence has emerged after their publication 6. The recommendation here is based on the most recent high-quality RCT evidence prioritizing morbidity and quality of life outcomes 1.