What is a Single-Use Viral Transport Tube (VTM)?

What is a Single-Use Viral Transport Tube (VTM)?

A Single-Use Viral Transport Tube, commonly known as a viral sampling tube or nucleic acid test (NAT) tube, is a sterile, pre-packaged medical device specifically designed for the collection, transportation, and storage of human respiratory samples (such as throat or nasopharyngeal swabs). It became widely recognized during the COVID-19 pandemic for its crucial role in mass testing.

Its primary purpose is to preserve the integrity of the virus (preventing RNA degradation) and ensure biosafety during the sample’s journey from the collection site to the testing laboratory.

Key Components and Functions

1. Tube Body:
   • Made of transparent plastic (like polypropylene, PP) to allow easy visual inspection of the liquid level.
   • Features clear volume graduation marks.
   • The cap typically contains a leak-proof seal to prevent spillage during transport.
2. Transport Medium (Preservation Liquid):
   This is the core component. Based on its formula and function, there are two main types:
   • Inactivated Viral Transport Medium:
     • Composition: Contains high concentrations of viral lysis salts (e.g., guanidinium salts) which rapidly break down the virus, rendering it non-infectious.
     • Advantages: High biosafety—significantly reduces the risk of secondary infection to healthcare and lab personnel. Effectively stabilizes and protects viral nucleic acid (RNA/DNA) from degradation.
     • Disadvantage: The virus is destroyed, making it unsuitable for tests requiring live virus, such as viral culture.
   • Non-Inactivated Viral Transport Medium:
     • Composition: Typically consists of Hank’s balanced salt solution, antibiotics, antifungals, and protein stabilizers (e.g., Bovine Serum Albumin).
     • Advantages: Preserves virus viability and integrity. Suitable for a wider range of tests beyond PCR, including viral culture, antigen tests, and antibody tests.
     • Disadvantage: Higher biosafety risk—the virus remains live and infectious, requiring strict handling and transport as a high-risk biological substance.
3. Swab:
   • Provided sterile and for single-use with the tube.
   • Tip Material: Now universally made from synthetic fibers (e.g., polyester, nylon flocked) instead of cotton. Cotton fibers can contain substances that inhibit the PCR reaction, affecting test accuracy.
   • Shaft: Made of plastic or notched wood, designed to be easily broken off after sampling so the cap can be closed securely.

Standard Workflow

1. Collection: A healthcare worker collects a sample from the patient’s throat or nasal cavity using the swab.
2. Preservation: The swab is immediately placed into the tube containing the transport medium. The shaft is snapped at the breakpoint, and the cap is tightened securely.
3. Transport: The sealed tubes are placed in a bio-safe transport container and shipped to the testing laboratory under cold chain conditions (typically 2-8°C) as soon as possible.
4. Testing: In the lab, a technologist opens the tube and uses a pipette to aspirate the liquid medium, from which nucleic acids are extracted for PCR amplification and detection.

Key Features and Importance

• Single-Use: Eliminates the risk of cross-contamination between samples, ensuring testing accuracy.
• Sterile: Prevents the sample from being contaminated by environmental bacteria or fungi, which could compromise the medium and the test result.
• Stabilizes Nucleic Acids: The medium contains ingredients that inhibit RNases, preventing viral RNA from degrading during transport. This is critical for obtaining reliable PCR results.
• Biosafety: Particularly with inactivated media, it greatly enhances the safety of personnel handling the samples.
• Traceability: Tubes are usually labeled with a unique barcode or QR code to link the sample to the patient’s information, enabling full-chain tracking and preventing mix-ups.