A-296 Streck Urine Preserve Provides Sample Stability for Cepheid Xpert CT/NG test
Authors: Connelly C M , Li J 
Published: October 2024

Background

Sexually transmitted infections (STIs) are one of the most common communicable diseases worldwide and are associated with significant morbidity and mortality. Data indicates that the four curable STIs - chlamydia, gonorrhea, trichomoniasis, and syphilis - cause over 375 million infections annually. Further, the infection rate for gonorrhea has increased by 63% in the United States and the emergence of resistant gonorrhea is an urgent global public health concern. To prevent transmission of gonorrhea and other curable STIs and minimize the escalation of untreated infections, early and effective prevention and control strategies are paramount. Rapid diagnostic testing and nucleic acid amplification tests (NAATs) have become the gold standard for STI detection. However, limited global access to these technologies often requires that samples be shipped to central laboratories for analysis. Current protocols recommend that neat urine be analyzed within 24 hours of collection if stored at 2 °C to 8 °C or within four days if frozen, as prolonged storage and exposure to freeze-thaws can induce cell lysis and release of nucleases, leading to degradation of DNA and false negative test results. Without sample stabilization, laboratories are left with a small window for accurate analysis. Here, we demonstrate that Streck Urine Preserve (SUP) maintains target and donor DNA concentrations during prolonged storage and that these stabilized samples are compatible with Cepheid’s automated GeneXpert System and associated Xpert CT/NG test.

Methods

Fresh human urine, with or without SUP, was tested neat or spiked with Neisseria gonorrhoeae (N. gonorrhoeae). Samples were stored at room temperature for up to 18 days before being analyzed on the Cepheid GeneXpert System using the Xpert CT/NG test per manufacturer’s instructions. Differences in average Ct values were compared for the sample processing control, sample adequacy control, and N. gonorrhoeae targets. DNA stability was assessed by comparing the changes between fresh and SUP-treated samples throughout the study period.

Results

Following prolonged storage, Ct values for neat, untreated urine increased by 3-7 cycles, correlating to a 10- to 100-fold decrease in detectable copies of N. gonorrhoeae and the sample adequacy control compared to urine samples stabilized with SUP. The average Ct value for samples stabilized with SUP did not change by more than 1.5 cycles throughout the study period. Additionally, Ct values for the sample processing control remained constant throughout the testing period, indicating that SUP did not impact sample processing.

Conclusions

When limited point-of-care testing options require storage and shipping of samples to central laboratories, urine stabilizers are imperative to obtain results representative of the patient sample at the time of collection. SUP effectively stabilized N. gonorrhoeae DNA and donor DNA prior to analysis with the Cepheid Xpert CT/NG test. This contrasts with the marked decrease in DNA copy number in non-stabilized urine over the study duration, which may lead to false negative results for low-positive urine samples. Taken together, SUP provides clinical researchers and assay developers with added flexibility when handling, shipping, and processing urine specimens and supports compatibility with automated NAAT systems and tests.