The purified total RNA is suitable for use in a variety of downstream applications, including: RT-PCR, RT-qPCR, Northern blotting, RNA sequencing, and so on. Serum/plasma samples are first lysed and homogenized in a strong denaturant and phenol containing buffer, which immediately inactivates RNases to ensure isolation of intact RNA. After addition of Buffer A, the homogenate is separated into aqueous and organic phases by centrifugation. RNA partitions to the upper, aqueous phase while DNA partitions to the interphase and proteins to the lower, organic phase or the interphase. The upper, aqueous phase is collected and mixed with Supplemental Reagent and ethanol. The liquid is then passed through the RNA binding Spin Column containing a silica-based membrane to which the RNA binds. Impurities are effectively removed by subsequent washing. The purified total RNA is then eluted with Elution Buffer and may be used in a variety of downstream applications.