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 β-subunit of human chorionic gonadotropin (hCGβ) concentrations in serum. The aim of this study was to explore the possibility of using quantitative analysis of total hCGβ 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 hCGβ concentration based on standard hCGβ samples, and used an IMR assay to detect total hCGβ 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 hCGβ 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 hCGβ. 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 hCGβ 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 hCGβ was noted (R(2)=0.862). CONCLUSION An IMR assay can quantitatively analyze total hCGβ concentrations in urine, and is a potential candidate for point-of-care testing to assist in the diagnosis of ectopic pregnancy.