A two-step procedure for extracting genomic DNA from dried blood spots on filter paper for polymerase chain reaction amplification

-based diagnostic tests. Traditionally alarge volume of blood is collected in tubes and DNA isextracted from white blood cells using a phenol–chloro-form method [1] or a “salting-out” rapid puri Wcation proce-dure [2]. While these methods are able to provide milligramquantities of puriWed DNA, this amount generally exceedsthat required for successful PCR and the methods are alsomore time consuming and expensive, and hence less suit-able for rapid PCR diagnosis, especially for multiple bloodsamples.The use of dried blood spots on Wlter paper becomes anattractive alternative to blood collection in tubes for PCRanalyses. First, only a small amount of blood is needed, andimmediate processing is not required. Second, there are notransfer steps once the blood is applied onto the paper andhence the chance for mislabeling or sample mixing is low.Third, sample transport and storage for dried blood spots iseasy and less expensive. As a result of these advantages, col-lection of blood on Wlter paper has been widely used for thePCR-based genetic screening [3–5].As blood samples contain a variety of substances thatmay inhibit PCR, separation of these substances fromDNA is generally necessary prior to ampli Wcation. To over-come this problem, a number of methods have been devel-oped for DNA extraction from dried blood spots on Wlterpaper, including the methanol method [6], the protease Kmethod [7], the Chelex-100 method [8], and the TE method[9]. Commercial products are also available, such as FTAcards and puriWcation reagent (Whatman, Middlesex, UK),but these products are relatively expensive, and the puriW-cation procedure requires multiple washing steps. Multisteppipetting is not only time consuming and incompatible withlarge numbers of samples, but will also increase the likeli-hood of cross-contamination.In this paper, we describe a simple but eYcient method(called the NaOH method in short) for extracting genomicDNA from dried blood samples stored for up to 5 years,which involves only one step of incubation in 20mMNaOH solution followed by a single wash with TE