Improved Method for Isolating Cell-Free DNA

Abstract

The quantity of DNA that can be isolated from human plasma/serum is very low and is frequently the limiting factor when a larger marker panel is to be used for genetic characterization of the DNA. In most of the recently published studies, commercially available columns were used for isolation of cell-free plasma/serum DNA, which made DNA isolation fast and allowed it to be standardized. Mandel and Metais (1) found ∼5.4 μg/mL total nucleic acids in the plasma in 10 healthy controls, and Stroun et al. (3) isolated between 150 ng/mL and 12 μg/mL DNA from the plasma of cancer patients. Much less DNA can be isolated with the aforementioned columns, however; we therefore wondered whether there are ways to increase the yield of free circulating DNA that can be isolated from plasma/serum and other body fluids. We compared the DNA yield from 1 mL of material, using 2 methods. Plasma and cell-free bronchial lavage supernatants (BL) were prepared as described (7). For the first method, we used the QIAamp DNA Blood Mini Kit (Qiagen) according to the manufacturer’s instructions. For the second method, we modified the DNA method described by Miller et al. (8).