1. Presented by Robert Kruse, MD, PhD and prepared by Lori Sokoll, PhD

Clinical Vignette

An elderly female presents with an unexpected hCG positive result at hospital admission. The patient has a past medical history of end-stage renal disease (ESRD) on dialysis, hypertension, secondary hyperparathyroidism, hypercalcemia, who now presents with left hip pain. Imaging reveals a femoral neck fracture. Of note, she also has a family history of osteoporosis and a smoking history.

At the time of her admission, her serum hCG (human chorionic gonadotropin) level was unexpectedly positive on a routine screen for female patients. Urine hCG testing was not performed since the patient is anuric secondary to ESRD. Creatinine was 4.5 mg/dL on the date of admission. The clinician initially paged the pathology resident in the chemistry lab asking if this hCG result could be a false positive. Upon quantification, the patient's serum hCG concentration was determined to be 177.4 mIU/mL.

Question:
Which of the following is the most likely source of this patient's positive hCG test?