Comparison of frozen and unfrozen blood spots for gene expression studies.

We studied gene expression in 9 sets of paired newborn blood spots stored for 8-10 years in either the frozen state or the unfrozen state. Fewer genes were expressed in unfrozen spots, but the average correlation coefficient for overall gene expression comparing the frozen and unfrozen state was 0.771 (95% CI, 0.700-0.828).