Bone marrow is composed of:
i. Reticulum cells and reticulum fibers
ii. Blood vessels and nerves
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iii. Haemopoietic cells and their mature stages
iv. Fat cells.
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Before deciding to examine the bone marrow, one should observe something abnormal in peripheral blood smear. Bone marrow biopsy can be obtained by the following three methods:
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1. Needle Aspiration
2. Microtrephine Biopsy
3. Surgical Biopsy
Needle Aspiration:
It is a simple, safe and relatively painless method and performed by using a special designed needle, such as Salah or Klema. The disadvantage of this technique is some marrow cells may be destroyed.
Microtrephine Biopsy:
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This method is not very simple but can be performed in OPD (out patient department) by using needles such as Jasshidi’s- swaim or Eslam. The method does not gives more than 0.3 ml of fluid at a time.
Surgical Biopsy:
This method is carried out under aseptic condition in operation theatre. The disadvantages of this method are: (a) It is difficult to repeat and (b) it is not advised in patients with leukemia and bleeding disorders.
Site of Biopsy:
i. Sternum
ii. Iliac crest
iii. Anterior and posterior iliac spine
iv. Upper end of tibia in children below 2 year
The aspirated material tends to clot rapidly; therefore, the smear should be made immediately after the aspiration of bone marrow.
Preparation of Bone Marrow Film:
Bone marrow films are made from bone marrow aspirate. Marrow contaminated with blood is not suitable for microscopic examination therefore; blood is removed from the aspirate before preparation of film. It is sucked with needles or sahlis pipette.
The yellowish irregular shape fragments are used to prepare smear. Place a drop of bone marrow aspirate on microscope slide. Bone marrow aspirate may contain some granular particles. These particles can be crushed with the help of another slide.
Place another slide over the first slide with bone marrow fluid. Put slight pressure on the second slide to crush the particles. Now separate the slide and with the help of spreader, prepare bone marrow smear. The smear should be about 3 to 4 cm in length and 1 to 1.5 cm in diameter.
At a time, about 3 smears should be prepared. Air dry the film and stain with any stain used for peripheral blood smear like Giemsas, Leishman or Wrights stain.
Bone marrow smear should be examined in tail region. Start with 10 × to 45 × to 100 ×. Now make differential count of large number of cells (300 to 1000) and calculate the % of each type of cell.
Normally, cellularity of bone marrow varies with age. It is more in infants and less in adults. In the bone marrow examination, first of all observe the erythropoietic cells, and then look for maturity of leucopoietic cells.
The cells appear as dark blue masses and fats as round vacuoles. Normal aspiration contains about 40% of fat cells and 60% of marrow cells.
In hypercellular aspiration, fat is reduced and in hypocellular aspiration fat is increased. It is necessary to note the following:
1. Stages of Erythropoiesis
2. Activity of erythrocytic cells and the ratio of myeloid— erythroid cells, i.e. ME ratio. In normal adult, ME ratio is 3: 4. The ME ratio at birth is 85:1. During the first week is 11: 1 and gradually decreases to 3: 1. Look for number and maturity of developing granulocyte.
Look for abnormal cells and toxic granules. Look for any abnormality in lymphocytes. Megakaryocytes and morphology of differential cell also observe for parasites and bacteria.
Clinical Significance:
Microscopic examination of bone marrow smear is useful for diagnosis of several haematologic disorders, such as acute leukemia, iron deficiency anaemia, and secondary deposits in bone marrow.
Aplastic anaemia, thrombocytopenia, diseases of reticulo-endothelial system and much other blood related disorders. ME ratio indicates the activity of bone marrow. ME ratio rises in leukemia and falls with leucopoiesis.