Blood is a common source of nucleic acid and it is often necessary to store blood samples before extracting the DNA/RNA of interest. We have tested the effects of various blood storage temperatures over time on the observed read N50 of DNA extracted from mammal blood (commercially available rabbit blood collected in K2-EDTA). All samples were processed according to a standard protocol; they were SPRI size-selected and sequenced using the Ligation Sequencing Kit (SQK-LSK109). The results below illustrate blood storage at room temperature leads to sample degredation (Figure 1), and storage at -20°C or below prevents sample deterioration both short and long term (Figure 2).

We recommend customers are aware of the effects of different blood storage conditions, and its influence on sequencing performance. For short term storage (7 days or fewer), it is recommended the blood is stored at 4°C or lower. For longer term storage (more than 7 days), it is recommended that the blood is stored at -20°C or lower.

Figure 1. The effect of short-term storage of blood at room temperature and at 4°C on the observed read N50 of DNA sequencing libraries. Rabbit blood, collected in K2-EDTA, was stored at room temperature or at 4°C before DNA was extracted at various points over the course of a week. Sequencing libraries were prepared from the DNA extracts using the Ligation Sequencing Kit and sequenced using MinION Mk 1B. These data show that storage at room temperature, even over short times, can result in sample degradation such that the extracted DNA may deliver lower read N50s, while storage at 4°C appears to ensure sample stability over this time period.

Figure 2. The effect of long-term storage of blood at -20°C and at -80°C on the observed read N50 of DNA sequencing libraries. Rabbit blood, collected in K2-EDTA, was stored at -20°C or at -80°C before DNA was extracted at various points over the course of six months. Sequencing libraries were prepared from the DNA extracts using the Ligation Sequencing Kit and the libraries were sequenced using MinION Mk 1B. These data show that storage at -20°C or -80°C, over a period of 12 months, appears to ensure sample stability as no deterioration in observed read N50s is observed.