Effect of storage temperature on cfRNA concentration in blood samples. Blood was drawn into K3EDTA tubes and BCTs (n = 10) and incubated at 6°C, 22°C or 30°C for 3 days, respectively. Plasma was then separated and cfRNA isolated. The cell free mRNAs for c-fos (A) and β-actin (B) were quantified by RT-qPCR. A significant increase in mRNA copy numbers for c-fos and β-actin was observed in blood stored in K3EDTA tubes at 6°C, 22°C and 30°C for 3 days, whereas samples stored in BCTs only showed a slight increase. Box plots show the median (line inside the box) and 75th and 25th percentiles (limits of the box). The upper and lower error bars indicate the 90th and 10th percentiles, respectively. The upper most and lower most dots indicate the maximum and minimum values.