|Sample Requirement||Turnaround Time|
|EDTA, fixed smears|
1-3 working days
These are not commonly collected from horses, only in cases that may have severe, undefined anaemia, severe persistent leucopenia or thrombo-cytopenia and in some cases of leukaemia.
Samples are most commonly collected from the wing of the ilium, the ribs or the sternum. sternal tap is recommended because it is most reliably productive. The ventral midline, under the sternum is clipped and prepared as if for surgical intervention. Local anaesthetic is infused into and under the skin of the ventral midline, just caudal to the olecranon, with the horse standing normally, restrained, sedated, in stocks. A bone marrow collection needle or an 18 gauge 3.5 inch spinal needle is introduced through a stab incision in the skin upwards to contact the sternum. The needle is then rotated with upward pressure until it enters the sternum, the stylette is removed and firm suction is used to aspirate a sample into a sterile 10 or 20 ml syringe, pre-treated with a few drops of 15% tripotassium EDTA to prevent clotting.
The sample is transferred to EDTA tubes and labelled for laboratory examination, without delay. If delay is inevitable, smears should be made and fixed, and sent with the wet samples, in case they are needed.
The cytopathological examination of bone marrow smears requires specific experience. Normal and abnormal cell types are classified and their relative proportions assessed. The normal equine myeloid:erythroid (M:E) ratio should be 0.5-1.5.