Measurement of mitochondrial DNA copy number in dried blood spots: A pilot study

Background: We evaluated the feasibility of mitochondrial DNA (mtDNA) copy number measurement in dried blood spots (DBS), its comparability with measurement in whole blood samples, and stability of mtDNA copy number from DBS over time. Methods: Women in this pilot study were participants in the Sister Study, a large prospective cohort. Sister Study participants provided a whole blood sample and DBS at enrollment. A second DBS sample was collected 5-10 years later from a subcohort of women with and without an incident breast cancer diagnosis between collections. Among 54 women (27 with breast cancer, 27 without) we measured mtDNA copy number from whole blood at enrollment and from DBS at both time points. Results: The average age at enrollment was 58.7 years (range:50-69). Values of mtDNA copy number measured in whole blood samples and DBS from enrollment were moderately correlated (Spearman R = 0.45; p = 0.005). Stability of mtDNA copy number in DBS from the two time points was moderate overall (ICC = 0.50) and similar between women with (ICC = 0.50) and without (ICC = 0.51) a breast cancer diagnosis between the two collections. Conclusions: Our results suggest that measurement of mtDNA copy number in DBS is feasible and may be a valid alternative to measurement in whole blood samples.