Quantitative analysis of total β-subunit of human chorionic gonadotropin concentration in urine by immunomagnetic reduction to assist in the diagnosis of ectopic pregnancy

Background: The initial diagnosis of ectopic pregnancy depends on physical examination, ultrasound, and serial measurements of total beta-subunit of human chorionic gonadotropin (hCG beta) concentrations in serum. The aim of this study was to explore the possibility of using quantitative analysis of total hCG beta in urine rather than in serum by immunomagnetic reduction (IMR) assay as an alternative method to diagnose an ectopic pregnancy. Methods: We established a standard calibration curve of IMR intensity against total hCG beta concentration based on standard hCG beta samples, and used an IMR assay to detect total hCG beta concentrations in the urine of pregnant women with lower abdominal pain and/or vaginal bleeding. The final diagnosis of ectopic pregnancy was based on ultrasound scans, operative findings, and pathology reports. In this prospective study, ten clinical samples were used to analyze the relationship of total hCG beta IMR signals between urine and serum. Furthermore, 20 clinical samples were used to analyze the relationship between urine IMR signals and serum levels of total hCG beta. Results: The calibration curve extended from 0.01 ng/mL to 10,000 ng/mL with an excellent correlation (R-2=0.999). In addition, an excellent correlation of total hCG beta IMR signals between urine and serum was noted (R-2=0.994). Furthermore, a high correlation between urine IMR signals and serum levels of total hCG beta was noted (R-2=0.862). Conclusion: An IMR assay can quantitatively analyze total hCG beta concentrations in urine, and is a potential candidate for point-of-care testing to assist in the diagnosis of ectopic pregnancy.