Received on November 21, 2008
Accepted on March 27, 2009

Endocrinology and Metabolism

False-Negative Results in Point-of-Care Qualitative Human Chorionic Gonadotropin (hCG) Devices Due to Excess hCG Core Fragment

¹ Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO
² Department of Clinical Chemistry, Helsinki University Central Hospital, Helsinki, Finland
³ Department of Pathology, Vanderbilt University, Nashville, TN
⁴ Barnes-Jewish Hospital, St. Louis, MO

^* To whom correspondence should be addressed. E-mail: gronowski{at}wustl.edu.

BACKGROUND: During pregnancy, hCG immunoreactivity in urine consists of intact hCG as well as a number of hCG variants including the core fragment of hCG (hCGcf). We identified 3 urine specimens with apparent false-negative results using the OSOM® hCG Combo Test (Genzyme Diagnostics) qualitative hCG device and sought to determine whether an excess of 1 of the fragments or variants might be the cause of the interference.

METHODS: We measured concentrations of hCG variants in the urine from 3 patients with apparent false-negative hCG results. Purified hCG variants were added to urines positive for hCG and tested using the OSOM, ICON® 25 hCG (Beckman Coulter), and hCG Combo SP® Brand (Cardinal Health) devices.

RESULTS: Dilution of these 3 urine samples resulted in positive results on the OSOM device. Quantification of hCG variants in each of the 3 patient urine specimens demonstrated that hCGcf occurred in molar excess of intact hCG. Addition of purified hCGcf to hCG-positive urines caused false-negative hCG results using the OSOM and ICON qualitative urine hCG devices.

CONCLUSIONS: Increased concentrations of hCGcf can cause false-negative results on the OSOM and ICON qualitative urine hCG devices.