How long can disease screening blood cards be kept in the refrigerator?

The disease screening blood card we often talk about is actually a dried blood spot card collected from peripheral blood/heel blood and dried. According to the conditions of being refrigerated at 2-8°C in a conventional household refrigerator and completely dry and sealed, the blood card for routine newborn genetic and metabolic disease screening can be stored for up to 6 months. If more sensitive tests such as viral antibodies, nucleic acids or drug concentrations are performed, the maximum storage time is 3 months. Even if they are stored in a -20°C freezer, it is not recommended to exceed 8 months. Even if the expired specimens appear to be intact, the test results are likely to be inaccurate.

I encountered this pitfall last month when I was helping the district CDC sort out the backlog of specimens. I had a blood card for influenza antibody screening that I collected early last year. At that time, I had no time to test it due to delays in the epidemic, so it was kept sealed in a refrigerator. This time I found it for re-examination, and the result was almost 30% different from the serum specimen collected and frozen during the same period. It completely failed to meet the laboratory quality control requirements and had to be discarded directly.

In fact, there is no completely unified conclusion on this storage period in the industry. Many veteran examiners who have been doing newborn screening for 20 to 30 years have an experience: as long as the blood card is completely dry and placed in a sealed bag with desiccant and does not get damp, it can still detect phenylketonuria and congenital onychomycosis after being stored at 2-8°C for 1 year. This type of obvious indicator abnormality can be reduced, but now the new clinical testing quality control standards are strict. As long as the blood card is stored for more than 6 months, even if an abnormality is detected, the subject must be asked to resample for review. This is because there is a fear of false negative and false positive results caused by the degradation of biological components, which will mislead clinical judgment.

Many people still have a misunderstanding, thinking that as long as they are put in the refrigerator, they will not be damaged. In fact, the most important prerequisite for preserving blood cards is to be sufficiently dry. After blood collection, the blood must be dried in a ventilated place at room temperature for at least 4 hours. Only when the blood spots are completely dry and no traces of moisture can be seen can it be bagged and sealed. Previously, a novice nurse from the community health service center in the jurisdiction rushed off work. After collecting 12 newborn screening blood cards, they were left to dry for only one hour before being bagged and stuffed in the refrigerator. When the samples were sent to our laboratory the next day, the entire batch of blood cards were damp and sticky, with hemolysis and mildew. We had to call parents one by one to recall them and retake them. In the end, we were complained about irregular service.

If you save the blood card not for recent testing, but for long-term purposes such as genetic tracing and disease risk screening, do not store it in a home refrigerator. After all, the temperature fluctuates greatly when it is turned on and off, and it is easy to transfer odors and bacteria on food, which will damage the specimen. If you really want to store it for a long time, it is best to send it to a professional biological sample bank and freeze it in an ultra-low temperature refrigerator at -80°C. Qualified nucleic acids can be extracted for testing after more than ten years.