Figure 1. Hemoglobin and MCV correlate with clinical hyperthyroidism. (A) Plot of Hemoglobin level (Hgb, g/dL) versus date is shown in the left panel. The vertical dotted line indicates the time of initiation of therapy for hyperthyroidism. (B) Plot of mean corpuscular volume (MCV, femtoliters, fL) versus date is shown in the right panel. Again, the vertical dotted line indicates the time of initiation of therapy for hyperthyroidism. Our patient developed clinical manifestations of hyperthyroidism/Graves’ disease beginning Sept 2020. Diagnosis was made and treatment started on 3/28/21 with methimazole 20 mg/d. The Hgb and MCV were decreased when the patient was floridly hyperthyroid, and then slowly returned to normal while he was under treatment for hyperthyroidism.