Abstract
Abstract Objective Decreased unconjugated estriol (uE3) concentrations increase calculated risk of Down syndrome. Therefore, falsely low uE3, due to assay interference, have the potential to cause false-positive screening results. Here we present a 35 years old woman with a pregnancy of 17+2 weeks. Materials and methods Second-trimester screening test was performed on the UniCelDxI 800 (Beckman Coulter, Brea, CA, USA) analyzer and her uE3 level was 0.21 ng/mL (0.21 MoM). Risk calculated for DS was 1/8. Measurements were repeated on IMMULITE 2000 XPi (Siemens Healthcare Diagnostics Inc., USA). uE3 result was 0.614 ng/mL (0.97 MoM). The risk for DS was negative with this system. There was no sign of fetal anomaly on three-dimensional ultrasound examination and cell-free fetal DNA screening test. We suspected assay interference for uE3. Results Serial dilutions of serum samples revealed nonlinearity. 36.3% increase was observed with heterophile antibody blocking tubes. The post-polyethylene glycol treatment resulted approximately the same uE3 levels as IMMULITE system. Addition of alkaline phosphatase Scavenger to serum increased the result by 90% showing that falsely low E3 result was due to an interferent reacting on assay medium. Conclusion Laboratories should be aware that falsely low uE3 results due to interference may be obtained.
Highlights
UE3 is measured, as a part of second-trimester DS screening tests and analysis of uE3 is always performed by immunoassay technique [1]
In enzyme-labeled immunoassays, the presence of inhibitors or activators of the detection enzyme may alter the signal and thereby the immunoassay results. This interference in immunoassays can be more difficult to identify in the setting of prenatal screening programs [3], where laboratory testing is applied to identify those at risk of a disorder, in a population who have not sought medical attention on account of symptoms of that disorder [4]
Three-dimensional ultrasound examination by an expert gynecologist was performed and there was no sign of fetal anomaly
Summary
UE3 is measured, as a part of second-trimester DS screening tests and analysis of uE3 is always performed by immunoassay technique [1] Interferents such as heterophile antibodies, human anti-animal antibodies, autoanalyte antibodies, rheumatoid factors (RFs) and other proteins in a patient sample, cross-react with the antibodies used [2] or assay detection components, such as streptavidin or ALP labels of reagents. In enzyme-labeled immunoassays, the presence of inhibitors or activators of the detection enzyme may alter the signal and thereby the immunoassay results This interference in immunoassays can be more difficult to identify in the setting of prenatal screening programs [3], where laboratory testing is applied to identify those at risk of a disorder, in a population who have not sought medical attention on account of symptoms of that disorder [4]. A percentage difference of ±25% was expected if no interference was present
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