Correlation between RNA integrity and rt-PCR experiments. The figure shows the correlation between RNA integrity values and the outcome of an real-time-PCR experiment, i.e. the average expression values of 4 housekeeping genes (GAPDH, KYNF, NEFL, β 2M). The vertical line is a meaningful threshold value for RIN classification, while the horizontal separates acceptable from unacceptable real-time PCR results, a) The RIN shows a strong correlation (0.52) to the expression value of the house keeping genes. A straightforward separation into positives and negatives is possible. b) The ribosomal ratio shows a poor correlation (0.24) to the expression value of the house keeping genes.