Is a serum vitamin B12 level of 818 pg/mL normal for a 1‑year‑old child?

A serum vitamin B12 level of 818 pg/mL is elevated but generally benign in a 1-year-old child and does not require treatment, though clinical follow-up is warranted to rule out rare underlying conditions.

Understanding the Normal Range

The reference range for vitamin B12 in 1-year-old children is approximately 345-1154 pg/mL 1. Your child's level of 818 pg/mL falls within the upper portion of this normal range, though it is on the higher side. Research specifically examining children aged 1-3 years establishes this range, and another study confirms that infants aged 0-1 year typically have values between 168-1116 pmol/L (approximately 227-1511 pg/mL when converted) 2.

Clinical Significance of This Level

This level is not concerning for deficiency and does not indicate toxicity. The 2024 NICE guidelines focus primarily on vitamin B12 deficiency (levels <180 ng/L or <133 pmol/L, which equals <180 pg/mL) rather than elevated levels 3. Your child's level is well above any deficiency threshold.

What Elevated B12 Might Mean

While elevated B12 is usually benign in children, recent evidence suggests monitoring is appropriate:

• Most cases are benign: A 2021 study following 40 children with B12 levels >1000 pg/mL found that most were otherwise healthy, with levels slightly decreasing at 3 months then remaining stable 4. Your child's level of 818 pg/mL is below this threshold.

• Rare associations with neurologic conditions: A 2025 study found elevated B12 levels (>660 pg/mL) were more common in children with neurologic disorders, particularly epilepsy, cerebral palsy, and developmental delays 5. However, this association doesn't mean elevated B12 causes these conditions—it may simply be a marker.

• Very rare malignancy risk: In the small subset of children with persistently very high levels (>1000 pg/mL), 2 out of 40 later developed leukemia 4. However, at 818 pg/mL, this risk is extremely low.

Recommended Clinical Approach

For a 1-year-old with B12 of 818 pg/mL:

1. Assess for symptoms: Look specifically for:

   • Developmental delays or regression
   • Seizures or abnormal movements
   • Feeding difficulties
   • Unexplained irritability

2. Review dietary intake:

   • Is the child receiving B12 supplementation or fortified formula?
   • Recent multivitamin use?
   • These are common benign causes of mildly elevated levels

3. Check for underlying conditions:

   • Liver disease (though structural liver disease is more relevant in adults) 6
   • Family history of autoimmune conditions
   • Any signs of hematologic abnormalities

4. Follow-up testing:

   • Recheck B12 in 3 months if no concerning features are present 4
   • If level remains >1000 pg/mL on repeat testing, consider complete blood count to screen for hematologic disorders
   • If neurologic symptoms are present, pursue appropriate neurologic evaluation regardless of B12 level

Key Pitfalls to Avoid

• Don't treat elevated B12: There is no indication for reducing B12 intake unless levels are persistently very high (>1000 pg/mL) and associated with supplementation
• Don't ignore persistent elevation: While one elevated value at 818 pg/mL is likely benign, persistently rising levels warrant investigation
• Don't assume elevated B12 means "too much supplementation": In the absence of exogenous B12 administration, elevated levels may reflect an underlying process

In practical terms, at 818 pg/mL with no symptoms, simple observation with repeat testing in 3 months is the most appropriate management 4.