Comparison of three different kits for extraction of high-quality RNA from frozen blood

Extraction of high-quality RNA is a crucial step in gene expression profiling. To achieve optimal RNA extraction from frozen blood, the performance of three RNA extraction kits- TRI reagent, PAXgene blood RNA system (PAXgene) and NucleoSpin RNA blood kit (NucleoSpin)- was evaluated. Fifteen blood specimens collected in tubes containing potassium ethylenediaminetetraacetic acid (EDTA) and stored at −80°C for approximately 5 years were randomly selected. The yield and purity of RNA, RIN (RNA integrity number) values and cycle threshold (Ct) values were assessed. Mean RNA yields with TRI reagent, PAXgene and NucleoSpin were 15.6 ± 8.7 μg/ml, 3.1 ± 1.7 μg/ml and 9.0 ± 5.5 μg/ml, respectively. Mean A(260)/(280) ratios of RNA for the three kits were 1.7 ± 0.1, 2.0 ± 0.1, and 2.0 ± 0.0, and mean RIN values recorded as 3.2 ± 0.8, 6.0 ± 1.1, and 6.4 ± 0.9, respectively. The Ct values of housekeeping genes, 18S rRNA, β-actin, RPLP0 and HPRT1, were as follows: TRI reagent (19.2 ± 1.6, 30.6 ± 1.8, 29.9 ± 1.4 and 36.3 ± 1.3), PAXgene 16.6 ± 1.4, 26.4 ± 1.3, 28.2 ± 1.8 and 33.8 ± 1.1), and NucleoSpin (16.3 ± 1.5, 27.2 ± 1.3, 27.0 ± 1.6 and 32.9 ± 1.6). RNA yield using TRI reagent was 1.7 times higher than that with NucleoSpin and 5 times higher than that with PAXgene. However, the purity and integrity of TRI-extracted RNA was lower than that extracted with PAXgene and NucleoSpin. Moreover, the Ct values of housekeeping genes after extraction with TRI reagent were approximately 1.7-3.8 times higher than those obtained with PAXgene and NucleoSpin. The PAXgene and NucleoSpin kits produced similar results in terms of RNA purity and integrity and subsequent gene amplification. However, RNA yields from NucleoSpin were 2.9-fold higher, compared to PAXgene. Based on these findings, we conclude that NucleoSpin is the most effective kit for extraction of abundant and high-quality RNA from frozen blood.