A family brings their 82-year-old grandmother to the emergency room stating that they cannot care for her anymore. They tell you, "She has just been getting sicker and sicker." Now she stays in bed and won't eat because of abdominal pain. She is too weak to go to the bathroom on her own. Her symptoms have been worsening over the past year, but she has refused to see a doctor. The patient denies symptoms of depression. Blood pressure is 90/54 with the patient supine; it drops to 76/40 when she stands. Heart and lungs are normal. Skin examination reveals a bronze coloring to the elbows and palmar creases. What laboratory abnormality would you expect to find in this patient?