Comparison of 2 human chorionic gonadotropin immunoassays commercially available for monitoring patients with gestational trophoblastic disease

Abstract

Objective: The aim of this study was to compare serumhuman chorionic gonadotropin (hCG) levels in patients with gestational trophoblastic disease (GTD) using 2 commercially available hCG immunoassays. Methods: Serum samples were obtained from patients with GTD attending the Botucatu Medical School Trophoblastic Diseases Center of São Paulo State University (UNESP), from November 2014 to October 2015. Serum hCG levels were measured with both Architect i2000SR and Immulite 2000 XPi chemiluminescence assays. Serum hCG levelswere compared against the null hypothesis. Agreement in clinical management decisions based on the hCG results was determined by comparing baseline hCG measurements and the hCG curves obtained with both assays. Results: Seventy-three patients with GTD were included in the analysis. Of these, 45 had hydatidiform mole and spontaneous remission, whereas 28 had gestational trophoblastic neoplasia (GTN).Therewas a perfect (zero difference) agreement in mean hCG levels between Immulite 2000 XPi and Architect i2000 when hCG is less than 100 mIU/mL. For hCG values greater than 100 mIU/mL, there was a significant difference between assays (P < 0.05), with levels measured via Architect i2000SR being higher than those measured by Immulite 2000 XPi in patientswith hydatidiform mole/spontaneous remission (R2= 90%, P < 0.01) and GTN (R2 = 98%, P < 0.01). Baseline clinical management decisions showed agreement in 100% (73/37) of cases (κ = 1.0, P < 0.001), whereas decisions based on hCG curve agreed in 98% (71/72) of cases (κ = 0.93, P < 0.001). Conclusions: Immulite 2000 XPi is the most frequently recommended assay for diagnosing and monitoring patients with GTD. However, our results suggest that because Immulite 2000 XPi and Architect i2000 show very similar performance in measuring hCG levels and in determining clinical management, Architect may be used as an alternative.