Real time polymerase chain reaction (RQ-PCR) represents one of the most sensitive methods for quantitative analysis of chimerism. This method is at least ten times more sensitive than commonly performed method of fragment analysis (FA) with fluorescence detection. Application of method that enables detection of microchimerism (mixed chimerism under 1%), can recognize relaps significantly sooner and in more cases than by using less sensitive methods. Performance of RQ-PCR within patients with sudden recurrence of autologous haematopoiesis showed microchimerism also in previous samples, formerly judged according to FA as complete donor chimerism (CDC). Furthermore, retrospective analysis of CDC samples from patient with positive residual disease repeatedly revealed microchimerism. Performance of more sensitive method can significantly contribute to early clinical intervention, nevertheless the predictable value of mixed chimerism and especially microchimerism must be further investigated.

        Key words: chimerism, microchimerism, real-time PCR, fragment analysis