For complete blood count, see topic 17. For diagnosis of multiple myeloma, see topic 15.

Flow cytometry

Cytometry means the analysis of certain properties of cells, like the number of cells, their size, the presence of certain cell surface proteins on them or inside the cell and so on. This technique is called flow cytometry because it lets cells flow through a very small tube and uses this to analyse their properties.

Flow cytometry can be used to measure a lot of things:

Determining immunophenotype of cells (determine the type of cancer)
Measure how many cells in a population express a specific antigen or protein
Determine DNA and RNA content in the cells
Evaluate the functions of cells, like the phagocytosis, chemotaxis or the intracellular [Ca2+]
Measure levels of cytokines
It can also sort cells

Let’s say we’d like to analyse the size of a bunch of cells in a Petri dish. We put these cells into a flow cytometer, which will direct the cells into a perfect, straight line of cells. The cells will then pass through a thin capillary, and a special laser is pointing straight at the capillary, so that the laser will pass through every single cell. The scattering of the laser when it hits a cell can be analysed by a computer that draws conclusions on the cell’s size.

To analyse what surface proteins are found on certain cells the cells must be labelled with antibodies labelled with fluorochromes, like in fluorescent microscopy. When cells labelled with these antibodies pass the laser can the machine differentiate cells based on their color.

Bone marrow aspiration and biopsy

Bone marrow aspirate and bone marrow biopsy are two examinations used in the evaluation of the bone marrow, indicated in case of unexplained haemotological disorder (like unexplained anaemia, leukopaenia, etc.) and in the evaluation of leukaemia and lymphoma.

Bone marrow aspiration involves aspirating a small part of the liquid bone marrow. This is technically more simple to perform and gives information on the number and features of the cells (cytological information) of the bone marrow. Bone marrow biopsy involves removing a solid piece of bone marrow, giving histological information. This is more technically difficult and more expensive to perform, and bone marrow biopsies require 2-3 days of processing before it can be examined.

Aspiration and biopsy both give complementary information and they are therefore usually performed together. Some conditions are better evaluated with aspiration and some are better evaluated with biopsy. They can be performed in the same setting.

Interpretation

When distinguishing acute from chronic haematological disorders of the bone marrow, one must determine the percentage of WBCs in the bone marrow which are blasts (immature). If > 20% of bone marrow cells are blasts, the disorder is acute (for example acute leukaemia).