Mismanagement of choriocarcinoma due to a false low HCG measurement.

Accurate measurement of HCG is essential for the diagnosis and management of patients with choriocarcinoma. It is therefore important that clinicians are aware of the possible analytical problems associated with the HCG assay if delay in the diagnosis of this curable tumor is to be avoided. We describe the case of a 43-year-old woman with extensive lung metastases who had an unnecessary hysterectomy and lung biopsy and in whom the diagnosis of this potentially rapidly fatal tumor was delayed because of a falsely low HCG level measured by a commercial kit. This underestimation of HCG was due to the 'high dose hook' effect, which is described in detail, and methods for avoiding this analytical problem are described.