Immunoassays for quantifying choriogonadotropin compared for assay performance and clinical application

Area of Science:

• Clinical Chemistry
• Immunoassay Technology
• Reproductive Endocrinology

Background:

• Accurate measurement of human chorionic gonadotropin (hCG) is crucial for diagnosing and monitoring various conditions, including pregnancy and trophoblastic diseases.
• Evaluating the performance of new automated immunoassay systems is essential to ensure reliable diagnostic capabilities.
• Comparison with established methods, such as immunoradiometric assays, provides a benchmark for assessing new technologies.

Purpose of the Study:

• To evaluate the calibration, accuracy, precision, sensitivity, specificity, and hook effect of revised automated hCG immunoassay systems (Baxter-Dade Stratus II, Abbott IMx intact hCG, and total beta hCG).
• To compare the performance of these automated systems with a widely used immunoradiometric assay (Hybritech).
• To assess the reliability of hCG measurements across different patient populations, including pregnant women, those with trophoblastic disease, and non-pregnant individuals.

Main Methods:

• Assessed calibration against the 3rd International Standard for all assays.
• Evaluated within-run and between-run precision for automated and immunoradiometric assays.
• Determined specificity for intact hCG and quantified free beta subunit and intact hCG beta subunit for the IMx total beta assay.
• Investigated hook effect and potential cross-reactivity in various patient samples.
• Assessed reliability at extreme calibration curve points and potential sample-probe carryover.

Main Results:

• All assays demonstrated clinically unimportant differences in calibration and were traceable to the 3rd International Standard.
• Automated instruments showed superior within-run precision, while between-run precision was similar across all assays.
• The Hybritech assay exhibited a clinically significant hook effect, absent in the Stratus and IMx assays up to 1.2 x 10(6) int. units/L.
• Results for pregnant women were comparable across all four assays.
• The IMx diluting module and extreme calibration points (<10, 800-1200 int. units/L) were found unreliable, unlike the Stratus system.
• Automated systems provided significantly faster hCG concentration estimates than the Hybritech assay.

Conclusions:

• Revised automated hCG immunoassays offer comparable clinical performance to traditional methods, with enhanced precision and a lack of hook effect.
• Automated systems provide a significant advantage in turnaround time for hCG testing.
• Limitations in the IMx system's calibration range necessitate careful interpretation of results at extreme values.
• Both automated systems, despite limited throughput, represent a valuable advancement in rapid hCG testing.