What is A Good VTM Kit for COVID-19

I. Viral RNA Preservation and Detection

A good VTM kit should preserve the viral RNA for accurate detection through real-time reverse transcriptase-polymerase chain reaction (rRT-PCR). In a performance comparison study, it was found that samples stored in properly formulated VTM kits consistently yielded high sensitivity and specificity. Specifically, studies showed that the sensitivity and specificity of the VTM-stored samples were both 100% for detecting SARS-CoV-2 when tested via rRT-PCR. For instance, in trials with known positive samples, the Ct (cycle threshold) values for key viral genes (N and ORF1ab) remained consistent over time, with Ct values ranging from 29.78 to 36.11 in effective VTM formulations.

II. Composition for Contamination Prevention

To prevent bacterial and fungal contamination, good VTM kits are typically supplemented with antimicrobial agents. Studies revealed that the addition of 0.5 µg/mL gentamicin sulfate and 100 µg/mL fluconazole is effective in inhibiting microbial growth. In microbiological tests, no colony-forming units (CFUs) were observed in samples tested with these antimicrobial concentrations, ensuring that the viral RNA remains intact without interference from contaminants.

III. Stability of the Medium

The stability of a VTM kit is crucial for preserving samples over time. Data showed that VTM stored at 4°C remains stable for up to four months. In accelerated stability studies conducted at room temperature (25°C) over four weeks, no significant change in pH, sterility, or viral detectability was observed. The predicted stability of the VTM at 4°C based on the Arrhenius equation suggested that the medium could remain effective for at least four months. During this period, viral RNA degradation is minimal, with Ct value deviations of less than 2 for key viral genes (N and ORF1ab) over 10 days of storage.

IV. pH Range and Viral Viability

A good VTM must maintain a pH within the physiological range. The optimal pH for viral RNA preservation is between 6.8 and 7.2. Studies showed that a VTM with a pH ranging from 6.86 to 6.93 allowed for reliable viral RNA detection. The nasopharyngeal environment's pH typically ranges from 6.10 to 7.92, and maintaining this range in the VTM prevents viral degradation.

V. Performance and Ct Value Analysis

A significant indicator of a good VTM is the preservation of low Ct values in rRT-PCR tests, which reflect high concentrations of viral RNA. In comparative studies with commercial VTMs, effective VTMs showed no significant difference in Ct values for the ORF1ab gene and a slight difference for the N gene. For instance, the mean Ct values for the N and ORF1ab genes were 31.51 ± 2.18 and 34.05 ± 3.45, respectively, in one trial. The statistical analysis showed that the p-value for the difference in Ct values between VTMs was greater than 0.05 for the ORF gene, indicating no significant difference. This demonstrates that a good VTM can reliably store viral specimens for extended periods without impacting the PCR detection threshold.

VI. Comparison of Positive and Negative Samples

In trials involving 70 known SARS-CoV-2 positive and negative samples stored in different VTMs, the results showed 100% concordance between the VTM-stored samples and the test outcomes. All 12 known positive samples were correctly identified as positive, and all 58 known negative samples were confirmed negative. Additionally, in a randomized study of 80 samples, 15 (18.75%) were positive, and 65 (81.25%) were negative when tested from samples stored in the VTM. This high level of accuracy underlines the effectiveness of the VTM in preserving the integrity of the samples.

VII. Long-Term Specimen Storage

For resource-limited settings, where delays in testing are common, the ability of a VTM to preserve viral RNA over time is critical. Studies show that samples stored at 4°C for up to 14 days yielded consistent rRT-PCR results with minimal Ct value deviation. Specifically, in the first 10 days of storage, Ct value deviations remained within ±2, indicating that delayed testing did not significantly impact viral RNA detectability.

How to get reliable VTM kits for this flu season

Mantacc VTM kit prioritize viral RNA preservation, contamination prevention, and stability over time. The statistical data from various studies demonstrate that our well-formulated VTM can maintain over 98% sensitivity and specificity for detecting SARS-CoV-2, while preventing microbial growth and preserving viral RNA for up to four months under recommended storage conditions. Stability in pH, reliable Ct value readings, and compatibility with existing PCR protocols further underline our high-quality VTM kit for COVID-19 diagnostics.

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