The storage conditions of cell – free DNA collection tubes are crucial for ensuring the quality of samples and the accuracy of test results. The main storage conditions are as follows:

I. Temperature Conditions

1. Short – term Storage (a few hours to a few days)
   Generally, cell – free DNA collection tubes can be stored at room temperature (15 – 25°C) for a short period. However, it is advisable to keep the storage time within a few hours to minimize the impact of cell metabolism in the blood and potential nucleases on cell – free DNA. For example, in the clinical testing process of some hospitals, if the sample can be processed within a few hours, room – temperature storage is a convenient option.
2. Long – term Storage (more than a few days)
   For samples that need to be stored for a long time, low – temperature storage is recommended. The most commonly used temperatures are – 20°C or – 80°C. At – 20°C, the biochemical reactions in the blood, including cell metabolism and the activity of nucleases, slow down significantly. While – 80°C provides an even better preservation effect, almost halting the activity of various enzymes in the cells and greatly extending the storage period of cell – free DNA. For instance, in some research institutions conducting large – scale sample collection and long – term research, samples are usually stored in ultra – low – temperature freezers at – 80°C.

II. Avoid Repeated Freezing and Thawing

1. Repeated freezing and thawing can cause the formation and dissolution of ice crystals in the blood sample. This process may damage the cell structure, release intracellular nucleases, and thus degrade cell – free DNA. Moreover, the formation of ice crystals may also cause physical damage to the cell – free DNA molecules themselves, affecting their integrity. Therefore, during storage and use, the repeated freezing and thawing of samples should be minimized as much as possible. For example, when designing experimental or clinical operation procedures, the number of times and the amount of samples to be used should be planned in advance, and enough samples should be taken out at one time for testing to avoid unnecessary freezing and thawing.

III. Prevent Sample Contamination

1. Physical Isolation
   Cell – free DNA collection tubes should be stored in a clean and dry environment and avoid contact with other substances that may contaminate the sample. It is best to place the collection tubes separately in a special sample box or storage rack to prevent contact with chemical reagents, other biological samples (especially those that may contain high – concentration nucleases), etc. For example, in the sample storage area of a laboratory, different types of samples should be stored in separate areas, and cell – free DNA collection tubes have their own independent storage space.
2. Prevent Microbial Contamination
   The growth and reproduction of microorganisms may produce various enzymes and metabolites that can damage cell – free DNA. Therefore, when collecting blood, it is necessary to ensure the sterility of the collection tube. At the same time, during the storage process, attention should also be paid to the cleanliness of the environment to avoid microbial contamination of the sample. For example, in the sample storage facilities of hospitals or laboratories, regular disinfection is essential.

IV. Appropriate Packaging and Labeling

1. Packaging Materials
   The collection tubes should be packaged with suitable materials, such as sealed bags or special sample protective sleeves. These packaging materials can prevent the samples from being damaged by external physical factors (such as collision and extrusion) and can also play a certain role in moisture – proofing. For example, some high – quality sealed bags are made of multi – layer materials, which can effectively block moisture and air, providing good protection for the collection tubes.
2. Clear and Accurate Labeling
   Both the collection tube and its packaging should be clearly and accurately labeled. The label content should include key information such as sample number, collection date, and patient information. This not only facilitates the management and tracking of samples but also enables accurate correspondence between samples and patients or research subjects when analyzing data and interpreting results. For example, in a large – scale genetic testing project, accurate labeling can ensure that the test results of each sample can be correctly feedback to the corresponding patient.