A 16-year-old girl (gravida 0, para 0) presented to the emergency department with a 2-week history of nausea, vomiting, vaginal spotting, and lower leg edema. On examination we found a palpable lower abdominal mass. The patient acknowledged recent sexual activity but denied having any sexually transmitted diseases. Molar pregnancy was suspected because of the typical “snowstorm” appearance observed with ultrasound examination. The quantitative serum β-subunit of human chorionic gonadotropin (β-hCG) concentration was 746.20 IU/L (reference interval, <0.5 to 2.90 IU/L; reportable interval, 0.5–1000 IU/L). The result of a qualitative urine hCG test, however, was negative. Human error was initially suspected as the cause of the negative result in the first qualitative urine hCG test. Two experienced and well-trained senior medical technologists repeated the urine hCG test twice, but the results were still negative. The patient’s nurse also indicated that she did not think there had been mislabeling of the urine sample. Because of this discrepancy, we …
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