The patient returned to her physician's office eight months later, again complaining of increased fatigue during the past
The physical examination was unremarkable, and the stool was negative for occult blood. Blood testing showed a hemoglobin level of 10.7 gm/dL; MCV, 79 Ám3; RDW, 13.3%; white blood cell count, 8,800/mm3; and platelet count, 248,000/mm3.
One month later, the hemoglobin level was 10.3 gm/dL; MCV, 79 Ám3; white blood cell count, 6,600/mm3; and platelet count, 261,000/ mm3. The patient's symptoms had not resolved, and she mentioned feeling cold even though it was late spring. Thyroid testing showed a free thyroxine level of 0.4 ng/dL (normal, 0.8-2.8) and a thyroid-stimulating hormone (TSH) level of 29.5 U/L (normal, 2-11). Thyroid hormone supplements were prescribed, resulting in resolution of all symptoms and restoration of normal hematologic values.
The recurrence of fatigue was cause for concern. Gastric cancer was a possibility, but there had been no evidence of bleeding or weight loss, and the earlier endoscopy had shown no evidence of cancer. The patient did note slight constipation, so the colonoscopy was justified, especially considering her age. Increasing the frequency of the B12 injections was not justified. Relapses of anemia can occur when patients stop taking the vitamin, but this patient had missed only one injection in the past eight months. Even if she had stopped the injections entirely, her body's reserve of B12 was so large that symptomatic deficiency would not have recurred for a year or two.
One clue to the source of her new symptoms was in the CBC. The hemoglobin level had dropped slightly, to 10.7 gm/dL, and the MCV had risen to 79 Ám3, while other values remained normal. Even though the MCV technically indicates microcytic anemia, in this patient it indicated a macrocytic condition.
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