Mild Positive Human Chorionic Gonadotropin in a Perimenopausal Female: Normal, Malignancy, or Phantom?

Patient: A 47-year-old female who was in good health. Past Medical and Laboratory History: A fine-needle aspiration biopsy of a dominant thyroid nodule in a multinodular goiter was performed and revealed papillary thyroid cancer. The patient underwent a total thyroidectomy complicated by transient post-operative hypocalcemia. The patient was withdrawn from thyroid hormone replacement therapy 6 weeks prior to referral for radioactive iodine remnant ablation therapy. Her past and current clinical laboratory results are shown in Table 1. Chief Complaint: None. Laboratory Findings: Table 1 shows thyroid laboratory values consistent with hypothyroidism as expected in the setting of withdrawal from levothyroxine therapy. A routine quantitative human chorionic gonadotropin (hCG, Centaur, Siemens Medical Solutions, Tarrytown, NY) was ordered to rule out pregnancy prior to radioactive iodine therapy. The patient was perimenopausal and last had menses a year ago although she had a recent episode of vaginal bleeding. The patient denied sexual intercourse over the previous 5 years. Based on the initial result, a urine hCG and repeat quantitative hCG was ordered 72 hours later to determine if the levels were changing (Table 1). The attending endocrinologists contacted the laboratory to determine if the hCG results were correct or whether there was some interference with the test result. The clinical laboratory conducted an investigation as to the potential cause of this mildly increased and unchanging value.