What is the ICD‑10‑CM code for vitamin B12 deficiency (including both anemia and non‑anemic forms)?

ICD-10-CM Codes for Vitamin B12 Deficiency

The ICD-10 code for vitamin B12 deficiency is D51, which encompasses all forms of vitamin B12 deficiency anemia. 1

Primary Code Structure

• D51 is the root code for vitamin B12 deficiency anemia in ICD-10-CM, covering both pernicious anemia and other forms of cobalamin deficiency with anemia. 1

Important Clinical Context for Coding Accuracy

Diagnostic Accuracy Concerns

• The positive predictive value of the D51 code in administrative databases is only 31.5-36.8% when validated against biochemical confirmation of B12 deficiency with anemia, meaning this code is frequently misapplied in clinical practice. 2
• When B12 deficiency without anemia is used as the reference standard, the PPV improves to 51.3%, but this still represents substantial coding inaccuracy. 2
• The PPV is significantly lower (22.2%) in patients actually receiving B12 supplementation compared to those not supplemented (63.9%), suggesting the code is often applied inappropriately to patients already treated or without true deficiency. 2

Clinical Definitions for Proper Code Application

• Only 18.9% of patients with documented vitamin B12 deficiency meet WHO criteria for pernicious anemia (Hb <13 g/dL for men or <12 g/dL for women, MCV ≥100 fL, serum B12 <200 pg/mL, and positive gastric parietal cell antibodies). 3
• Among B12-deficient patients, 38.9% have anemia by hemoglobin criteria, 41.1% have macrocytosis (MCV ≥100 fL), and 47.8% have positive gastric parietal cell antibodies, but these features do not always overlap. 3

Coding Guidance Based on Clinical Presentation

When D51 is Appropriate

• Use D51 when the patient has confirmed vitamin B12 deficiency (serum B12 <180 pg/mL or <150 pmol/L) AND documented anemia (Hb <13 g/dL for men, <12 g/dL for women). 1, 4
• The code applies regardless of whether the deficiency is due to pernicious anemia, dietary insufficiency, malabsorption, or medication-induced causes. 4, 5

When Alternative Coding May Be Needed

• For patients with biochemically confirmed B12 deficiency (low serum B12, elevated methylmalonic acid >271 nmol/L) but without anemia, consider that D51 may not accurately capture the clinical scenario, as this code specifically denotes deficiency anemia. 1, 2
• Up to 50% of patients with metabolic B12 deficiency have normal serum B12 levels but elevated methylmalonic acid, representing functional deficiency that may not be captured by standard coding. 1

Common Clinical Pitfalls in B12 Deficiency Coding

• Neurological manifestations of B12 deficiency often appear before hematological changes, so patients may have severe neurological symptoms (paresthesias, ataxia, cognitive impairment) without meeting anemia criteria for D51. 4, 6
• Macrocytosis (MCV ≥100 fL) precedes anemia development and is often the earliest laboratory sign, but macrocytosis alone without anemia may not warrant the D51 code. 1
• Food-bound cobalamin malabsorption is now the most common cause of B12 deficiency, not pernicious anemia, yet the coding system does not distinguish between etiologies. 6

High-Risk Populations Requiring Screening

• Adults >75 years (18.1% have metabolic deficiency), metformin use >4 months, PPI or H2-blocker use >12 months, gastric/intestinal resection, inflammatory bowel disease, and strict vegetarians/vegans all warrant screening. 1, 5
• Post-bariatric surgery patients have permanent B12 malabsorption requiring lifelong supplementation. 1, 5