A 43-year-old woman has had increasing difficulty swallowing over the past year. She notices that her hands turn white and are painful on exposure to cold. She remarks, "I may be getting older, but at least I don't have any wrinkles on my face or hands yet." On physical examination, her blood pressure is 115/75 mm Hg. The skin of her face and hands appears taut and shiny. A punch biopsy specimen of the skin of the hand shows dermal collagenous fibrosis and focal calcification. She receives yearly esophageal dilation for the next 20 years, during which time she develops no serious illnesses. Which of the following serologic test results is most likely to be positive in this woman?