False elevation of human chorionic gonadotropin in a patient with testicular cancer

Background. A 44-year-old, HIV-positive man presented with a painless swelling of his left testicle. He underwent left radical orchiectomy for a pathological stage T1 nonseminomatous germ cell tumor (NSGCT). A persistently elevated postoperative human chorionic gonadotropin (hCG) level resulted in the patient being diagnosed as having low-risk, stage 1S disseminated NSGCT. He was treated with four cycles of etoposide and cisplatin chemotherapy, but his hCG level had not returned to normal at the end of the treatment. Postchemotherapy CT showed no evidence of metastatic disease. Investigations. Measurement of serum levels of tumor markers, including a-fetoprotein, hCG and lactate dehydrogenase, scrotal ultrasonography, HIV-1 reverse transcriptase polymerase chain reaction, CT of the thorax, abdomen and pelvis, assessment of kidney function, and measurement of follicle-stimulating hormone and luteinizing hormone levels. Diagnosis. Falsely elevated serum hCG level caused by heterophile antibody interference in the hCG immunoassay. Management. The patient's postchemotherapy serum samples were reanalyzed using a heterophile antibody blocking agent, the results of which showed no detectable hCG. No salvage therapy was required, and the patient remains in complete remission.