Hi Chirley,
As far as I understand different researchers get different results. Here they report that 68% of bone marrow samples from 100 MDS patients showed an abnormal karyotype by conventional cytogenetic studies and/or interphase fluorescence in situ hybridization (FISH) but only 31% of peripheral blood samples from the same patients were abnormal. They recommend that bone marrow should be tested at diagnosis.
http://www.ncbi.nlm.nih.gov/pubmed/22537394
Kind regards
Birgitta-A