The DNA in blood samples (hereinafter referred to as "blood DNA") is used for the purposes of diagnosis of genetic diseases, diagnosis and monitoring of blood-borne parasitic diseases such as malaria, the determination of paternity, and the monitoring of other unusual cell populations in the blood as can occur in some neoplasias. For these purposes, the term "blood DNA" is used to cover all sources of DNA commonly found in blood, and thus includes the DNA of the human patient from whom the blood sample was obtained, as well as the DNA in any other organisms circulating within his/her blood.
It is a principal object of the present invention to provide a solid medium and method whereby DNA, particularly DNA in blood samples, may be conveniently and reliably stored, and if desired transported (for example from a hospital or doctor's surgery to a pathology laboratory), in a form suitable for either the recovery of the DNA for analysis or the use of the DNA in situ on the solid medium.
In the past, blood DNA has been transported as purified DNA, liquid blood, frozen blood or blood dried onto paper, however, all these methods have disadvantages. Transport of blood DNA as dried, purified DNA is most desirable, but it requires a high standard of technical assistance to be available at the places of collection. Thus, since such technical assistance is usually not available at the collection places, whole blood or other crude samples are usually sent to a central facility where the DNA is purified. Transport of liquid blood involves the need for sterility of collection and this is extremely inconvenient under some circumstances, e.g. where the sample is a heel-prick taken from an infant. The transport of liquid blood or frozen blood also demands temperature control and an appropriate transport system other than the regular postal system. This is true even before the question of hygiene is considered. In addition, the modern problems with pathogens such as the "AIDS" virus completely rule out the transport of any potentially infective liquid or frozen sample except under proper and expensive supervision.
Blood dried onto filter paper is a proven alternative to the above procedures and it has been shown that DNA can be extracted and isolated from dried whole blood spots in a form and in sufficient quantities for use in DNA analysis.sup.1. This procedure still suffers from a number of disadvantages. Thus, there has been no deliberate and rapid destruction of most pathogens, and there has been no deliberate inhibition of the processes degrading the DNA other than that caused by desiccation. Slow desiccation or even a small degree of rehydration under conditions of high relative humidity will allow the growth of DNA-destroying microflora. Even in the presence of bacteriostatic agents of the type that do not denature proteins, there will be conditions that permit enzymic-autolytic breakdown of the DNA and some nonenzymic breakdown of the DNA (in enzymic-autolytic breakdown, dying or damaged tissues, either human cells or parasite cells, activate enzymes that degrade their own components). There is also considerable difficulty desorbing very high molecular weight DNA from paper, if this is required. Surface adsorption effects can cause losses of DNA and this will cause the preferential loss of the least degraded, i.e. the most desired class of DNA molecules.