Patients with sickle cell anemia often are given folate supplementation on the premise that their chronic hemolytic anemia might lead to folate depletion. However, clinical folate deficiency rarely occurs in patients with sickle cell anemia, and folate supplements carry the risk of partially concealing the megaloblastic changes that would typically occur in patients who develop concomitant vitamin B₁₂ deficiency. Dhar and colleagues present a case report of a patient with sickle cell anemia in whom B₁₂ deficiency remained undetected until severe neuropsychologic sequelae occurred.

The patient was diagnosed with sickle cell anemia when she was eight years old. After the initial diagnosis, no sickle crises or transfusions occurred until she became pregnant in her adolescent years. At this time, folate supplementation was initiated. An elevated red blood cell mean corpuscular volume was noted during her first pregnancy, but her serum cobalamin level was normal. Seven years later, she began to develop frequent painful sickle crises. Despite oral iron and folate supplements, her hemoglobin level declined to as low as 5.4 g per dL (54 g per L), necessitating frequent transfusions. Over the following year, her mental status declined markedly, and congestive heart failure developed because of severe anemia.

A subsequent hospitalization for a fall and ankle injury led to recognition of the pernicious anemia that was complicating her sickle cell disease. Her serum cobalamin level was mildly depressed at 124 ng per L (92 pmol per L; normal range, 211 to 911 ng per L [156 to 672 pmol per L]), but her serum methyl-malonic acid level was elevated at 1,320 mcg per L (normal range: 6.6 to 37.0 mcg per L). The detection of serum antibodies to intrinsic factor and an elevated serum gastrin level confirmed the diagnosis of pernicious anemia. Her mental status and anemia rapidly improved with vitamin B₁₂ supplementation, and she achieved complete normalization of both factors after nine months of treatment. No further sickle crises or transfusions occurred.

The authors conclude that routine folate supplementation in patients with sickle cell anemia deserves reconsideration, because few of them are folate-depleted, and those who develop concomitant vitamin B₁₂ deficiency may be harmed by delayed diagnosis.