MicroRNAs are short RNAs which can be utilized as biomarkers for a variety of conditions. They are detectable in serum, and changes in the levels of circulating microRNAs have been associated with different diseases. We tested for the presence of microRNAs in serum that is dried on paper and stored unrefrigerated instead of being kept frozen. MicroRNAs were readily detectable in such blots, and their detectability was improved by using paper made of cellulose instead of glass fiber, and by re-hydrating dried blots with Trizol™ instead of water, phosphate-buffered saline, or guanidine hydrochloride before RNA extraction. MicroRNA preservation was not diminished by drying of blots at 37, 45 or 60 ºC instead of room temperature or by storage of blots at 37, 45 or 60 ºC instead of room temperature, but was worse when blots were dried incompletely or exposed to high humidity during storage. Preservation of microRNAs in serum was not adversely affected if instead of being kept frozen at -80 ºC it was stored as dried blots at room temperature or 37 ºC for ten or eight and a half months, respectively. In a group of ten individuals, microRNA quantifications of -80 ºC-frozen or dried sera stored at room temperature correlated well. Dried blots may thus be a convenient and safer way to save, transport, and store serum without refrigeration for microRNA assays
