B12 Deficiency-Induced Hemolytic Anemia With an Extensive Deep Vein Thrombosis.

Vitamin B12 deficiency is a commonly encountered condition in both inpatient and outpatient settings. However, in severe cases, it can have many hematologic complications that can be life-threatening. We present a 56-year-old African American female patient presenting with fatigue found to have a B12 deficiency with elevated methylmalonic levels with simultaneous hemolytic anemia, pancytopenia, and an extensive deep vein thrombosis (DVT) involving her lower extremities. Labs showed anemia, thrombocytopenia, macrocytosis, elevated lactate dehydrogenase (LDH), low haptoglobin, elevated D-dimer, and a positive intrinsic factor blocking antibody leading to a diagnosis of pernicious anemia. Along with anticoagulation, the patient was recommended intramuscular B12 injections daily for seven days followed by weekly and then monthly. Here, we emphasize that B12 deficiency can be life-threatening and requires a high index of suspicion for early recognition of various downstream effects for appropriate management and treatment.