Standardisation of molecular diagnostics is fundamental for effective application of genetic analyses in personalised medicine. The amount of DNA extracted from a specimen can have a significant impact on diagnostic accuracy especially in cases where the diagnostic variant has a low concentration such as cancer.

Blood and tissue samples were supplied to genetic laboratories to assess the reproducibility of extraction methodologies; DNA was extracted using participants’ routine procedures and returned to the External Quality Assessment provider. The amount of DNA was measured by two independent analytical techniques, fluorescence intensity of intercalating dye and digital PCR; DNA quality was evaluated by DNA integrity number scores.

The amount of DNA extracted varied widely between and within participants and for different blood volumes indicating that consistent diagnostic quality is challenging even within a single test centre. The median dPCR measured amount of DNA was on average six times higher than the intercalating dye measurements obtained in this study, indicating the possibility that the latter quantitative method may significantly underestimate the amount of DNA thus making it not fit for purpose.

Standardisation of genetic diagnostic tests will require a significant improvement in the reproducibility of DNA extraction; this could be achieved if suppliers and users of DNA extraction kits validate their extraction methodology using reliable quantitative measurements or reference materials.