In classical cytogenetics, single chromosomes are examined visually. The following characteristics can be described: number of chromosomes per cell, lack or increase of chromosomes, multiplication or loss of single chromosome segments, dislocation and translocation betrween chromosomes or abnormal orientation of chromosome segments. Besides the application in genetics (constitutive anomalies of chromosmes in hereditary diseases), the demonstration of acquired chromosomal aberrations is of great importance in different hematological neoplasms.
For cytogenetic examination, cells must be cultivated and brought into cell division. Dividing cells are retained in metaphase by the use of inhibitors of the spindle apparatus. Thus, chromosomes become solitarily visible and can be examined by microscope. After staining with e.g. Giemsa, chromosomes show a characteristic banding (G-Banding). This banding allows for a specific attribution of even smallest pieces of chromosomes to specific chromosomes.
Cytogenetics play an important role in the diagnosis of acute myelocytic leukemia, acute lymphocytic leukemia, chronic myelocytic leukemia (CML), myelodysplastic syndromes and other hematological neoplasms. Cytogenetic aberrations help to exactly classify certain hematological diseases and are often of prognostic importance.
Since cells have to be cultivated, the material must reach the laboratory within 24 hours and must be processed immediately. In hematological diseases, bone marrow aspirate with heparin is used. Only if there are sufficiently high numbers of blasts, peripheral blood can be used in the diagnosis of acute leukemias and myelodysplastic syndromes.