Bone marrow biopsy is an important diagnostic test in multiple myeloma. Bone marrow biopsy consists of the collection of the bone marrow aspirate and the solid core biopsy. Tests that can be performed on the bone marrow biopsy include karyotyping (chromosomal analysis) and immunophenotyping.

• Bone marrow biopsy is usually performed in most patients with a suspected diagnosis of multiple myeloma or other hematologic malignancy. It is usually done as part of the initial diagnostic workup.
• Bone marrow biopsy is usually performed to estimate the percentage of bone marrow occupied by plasma cells.^[1]
• Bone marrow biopsy consists of both a liquid aspirate and a solid core biopsy. Immunophenotyping (flow cytometry) is usually done on the bone marrow aspirate to assess for abnormal cells. Of note, plasma cells are particularly susceptible to mechanical damage by immunophenotyping, so this is not the best way to assess for plasma cell burden in the bone marrow. A better method is to assess the core biopsy for plasma cell content.
• Karyotyping detects any chromosomal abnormalities in multiple myeloma cells such as chromosome 13 deletion.^[1][2] Cytogenetics (chromosome analysis) can be performed on the core biopsy. Molecular studies are usually performed on the aspirate. Certain cytogenetic abnormalities have prognostic significance.
• The percentage of plasma cells is used of one of the key diagnostic criteria of multiple myeloma.^[1] A diagnosis of multiple myeloma requires greater than 10% clonal plasma cells in the bone marrow.
• Fluorescent in situ hybridization (FISH) detects any chromosomal abnormalities occurring in multiple myeloma such as chromosome 14 translocation.^[1][2]