P2.207: A Hidden Past: An Unexpected Anemia in an Adopted Adolescent

Introduction: We present a case of a rare etiology of anemia which was further masked by an incomplete medical history due to an undisclosed adoption history.

Case Description: A 16-year-old male presented with two weeks of jaundice, pallor, and intermittent vomiting. He experienced dizziness when standing and breathlessness while running. He reported unintentional 20-lb weight loss over six months but denied fatigue, pruritus, or chest pain. He and his parents reported no past medical history and no family history of anemia or hematologic disorders.

On exam, he was comfortable appearing with scleral icterus, jaundice, and pallor. He had a normal abdominal exam without hepatosplenomegaly. He had no lymphadenopathy, petechiae, or bruising.

Complete blood count revealed leukopenia (WBC 3.86 thou/uL), macrocytic anemia (Hb 6.8 g/dL, MCV 113.2 FL), and normal platelet count (162 thou/uL). Absolute reticulocyte count was not increased (27.2 BIL/L). Lactate dehydrogenase was elevated (7500 U/L). Uric acid was also elevated (7.4 mg/dL) with elevated plasma free hemoglobin (130 mg/dL).

A metabolic panel revealed a transaminitis (AST 258 U/L, ALT 114 U/L) with mild hyperbilirubinemia (Tbili 1.9 mg/dL). His blood type was O positive, DAT negative. A peripheral blood smear was obtained (Figure 1).

Given his macrocytosis, his ED workup included B12 and folate levels, which later returned with markedly low B12 ( < 50 pg/mL). He was admitted to the Hematology service. His B12 deficiency was further supported by elevated methylmalonic acid (3.84 umol/L) and homocysteine (150 umol/L). Additional laboratory tests, including flow cytometry, copper level, plasma free hemoglobin, and hemoglobin electrophoresis, were normal. ADAMTS13 activity was higher than 10%, which was reassuring against thrombotic thrombocytopenic purpura.

During hospitalization, the family revealed the patient was adopted and previously needed "B vitamin injections." His former out-of-state medical team was contacted and revealed his B12 deficiency was due to an underlying rare autosomal recessive intrinsic factor deficiency.

He was diagnosed with microangiopathic hemolytic anemia secondary to B12 deficiency due to autosomal recessive intrinsic factor deficiency. He was re-initiated on B12 injections, and follow-up lab work showed an appropriate response.

Discussion: This case underscores the diagnostic complexity of an incomplete medical history. Severe B12 deficiency can cause life-threatening hematologic abnormalities, including pancytopenia, microangiopathy, and severe anemia. Congenital intrinsic factor deficiency is rare, affecting less than one in a million. The initial presentation is often nonspecific, including failure to thrive, symptomatic anemia, and peripheral neuropathies. It is typically diagnosed before age five and responds well to B12 supplementation via intramuscular injections. In this case, delayed discovery of his adoption and previous B12 treatment further complicated his diagnostic picture.

Conclusion: This case underscores the importance of a thorough medical and social history and emphasizes the need for broad diagnostic consideration in unexplained anemia.