Persistent low levels of serum hCG due to heterophilic mouse antibodies: an unrecognized pitfall in the diagnosis of trophoblastic disease

Abstract

Phantom hCG refers to persistent mild elevations of hCG, leading physicians to unnecessary treatments whereas neither a true hCG nor a trophoblastic disease is present. We report the case of a 23-year-old woman with persistent low levels of serum hCG detected one month after miscarriage. As choriocarcinoma was suspected, a chemotherapy trial of methotrexate was prescribed, without any hCG reduction. Subsequently, laparoscopy ruled out a trophoblastic residue and the patient was referred to the Endocrine Unit for further investigations. While low levels of hCG were still detected in serum, no hCG was detected in the urine. In addition, when serum was processed in a HBT tube for revealing heterophilic antibodies, hCG was no longer detected. Such finding indicated the presence of phantom hCG due to heterophilic mouse antibodies interaction. This case raises the need of clinico-biological discussion to avoid inappropriate therapeutic decisions. Based on this case experience and after review of the literature, we suggest that current gynecological protocols for the diagnosis and treatment of trophoblastic disease should consider the inclusion of urinary hCG and/or a test for serum heterophilic antibodies when appropriate.

Chinese abstract

幻影hCG是指既没有真正的hCG升高也无滋养层细胞疾病存在，血清中出现持续低水平的hCG，导致医生进行不必要的治疗。我们报告的一个23岁的女性在流产一个月后存在持续低水平的血清hCG。怀疑绒毛膜癌，行甲氨蝶呤化疗，但没有任何hCG的减少。随后，腹腔镜检查排除了滋养层的残余，病人被送往内分泌科进一步诊治。尽管血清hCG持续低水平，尿hCG检测并未显示升高。此外，当血清放置在HBT管以排除异嗜性的抗体的干扰时，则检测不到hCG。这些发现表明了存在与异嗜性的老鼠抗体的相互作用的幻影hCG。这例病人引发了为避免不恰当的治疗的临床生物学讨论。回顾这个案例，我们建议目前妇科诊断与治疗滋养层疾病的方案应该适当考虑检测尿hCG以及血清异嗜性抗体。

• Heterophilic mouse antibodies
• phantom hCG
• serum hCG
• trophoblastic disease

Acknowledgements

The authors are grateful to Dr J. Texeira and Dr J. Haleng for the technical assistance and to Dr GL Tamagno (Mater Misericordiae University Hospital, Dublin, Ireland) for revising the manuscript.

Declaration of interest

The authors report the absence of conflicts of interest.