ICD-10 Code D51.2 – Transcobalamin II deficiency (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code D51.2 – Transcobalamin II deficiency
What it is
D51.2 identifies a congenital problem with transcobalamin II, the protein that transports vitamin B12 into cells. It is used when the deficiency causes impaired cellular B12 delivery and related hematologic or metabolic disease.
Clinical signs
Clinical features vary; refer to documentation. Commonly documented findings include megaloblastic anemia, poor growth or failure to thrive, recurrent infections, and neurologic or developmental concerns related to vitamin B12 deficiency.
When to use this code
Use D51.2 when the provider documents transcobalamin II deficiency, congenital B12 transport defect, or a confirmed inherited disorder of cobalamin transport. You may also use it when the chart clearly links the anemia or metabolic findings to this specific deficiency.
Do not substitute this code for nonspecific vitamin B12 deficiency unless transcobalamin II deficiency is stated or clearly established. Check documentation if the record only mentions low B12, anemia, or malabsorption without the transport defect.
Do not use for
Do not use D51.2 for dietary vitamin B12 deficiency, pernicious anemia, or other causes of B12 deficiency that are separately documented. Check documentation when the cause is unclear.
Coding tip
Look for wording such as “transcobalamin II deficiency” or “B12 transport defect” in the assessment before assigning D51.2.