Circulating DNA in plasma and serum: Biology, preanalytical issues and diagnostic applications

The recent studies in circulating nucleic acids have brought about a new dimension to medical diagnostics. In oncology, various tumorassociated molecular alterations have been detected in the plasma/serum of cancer patients. These findings have important implications for the diagnosis, prognostication and monitoring of many types of malignancies. In pregnancy, the discovery of fetal DNA in maternal circulation has opened up a new source of fetal genetic material for noninvasive analysis for numerous fetal conditions and detection of certain pregnancyassociated disorders. The measurement of circulating DNA has also found potential application in the posttreatment monitoring of transplant patients and the assessment and prognostication of trauma patients. Although much attention has focused on circulating DNA, the knowledge of its biology is still at an early stage. For example, the origin and mechanisms of release of circulating DNA remain to be elucidated. The eventual clinical application of circulating DNA technology would also require the thorough elucidation of preanalytical factors that may affect its measurement in clinical laboratories.