An older adult client with new-onset atrial fibrillation is sweating excessively. After reviewing the client's recent laboratory results, the nurse concludes that which might be causing the client's symptoms?
A) A hemoglobin (Hgb) level of 11.0 g/dL
B) A thyroid-stimulating hormone (TSH) level of 0.25 mU/mL
C) A TSH level of 18 mU/mL
D) A Hgb level of 13.8 g/dL