You are answering a USMLE-style medical question. Question: A 54-year-old woman presents with fatigue, malaise, and shortness of breath over the past 5 months. Past medical history is significant for rheumatoid arthritis diagnosed 23 years ago for which she takes naproxen as needed. Her vital signs include: temperature 36.9°C (98.4°F), blood pressure 135/88 mm Hg, pulse 92/min. Physical examination is significant for conjunctival pallor and bilateral ulnar deviation of the metacarpophalangeal joints. Laboratory findings are significant for the following: Hemoglobin 9.2 g/dL Mean corpuscular volume 76 fL Leukocyte count 7,000/mm3 Platelet count 220,000/mm3 Serum ferritin 310 ng/mL Erythrocyte sedimentation rate 85 mm/h Which of the following is a feature of this patient's anemia? Options: A) ↑ serum transferrin receptors B) ↑ transferrin saturation C) Upregulation of hepcidin D) ↑ reticulocyte count Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.