Bronchoalveolar lavage is the diagnostic method for the lower respiratory system. A bronchoscope is passed from the mouth and nose into an appropriate airway in the lungs, with a measured amount of fluid introduced and after that collected for examination.

Analysis of BAL fluid cell counts, cytology, and culture provides insights into immunologic, inflammatory, neoplastic, and infectious processes occurring at the alveolar level.

Cytological Evaluation

Bronchoalveolar lavage (BAL) samples taken from the same bronchi were pooled together for every individual, for a total of 2 pooled samples per ferret. The macroscopic examination of the color and turbidity of the BAL fluid have to be described, and the amount of lavage fluid recovered is to be recorded. 

Leukocytes and erythrocytes are counted in the well-mixed undiluted fluid using an improved Neubauer hemocytometer two cytospin smears, 1 of 400 μl and 1 of 200 μl, of the fluid samples, are then prepared by centrifugation at 1000 × g for 5 mins. 

If mucus is present, it is to be isolated and applied on a slide using a squash preparation technique. A Romanowsky stain is applied to the cytospin smears. Microscopic evaluation is done blindly by a board-certified veterinary clinical pathologist. This consists of an overall analysis using a 10× objective lens on all slides and a 300-cell leukocyte differential count on slides from each side of the lung, using a 50× oil-immersion objective lens.

Histological Examination

Five ferrets should be humanely euthanized with the intravascular injection of barbiturates (pentobarbital), 110 mg/kg BW after anesthetic induction with isoflurane, which is delivered through a facemask. The remaining 7 ferrets were fostered by the small mammal shelter. All respiratory systems of the euthanized ferrets were grossly examined and after that fixed with intratracheal instillation of 10% neutral-buffered formalin; the larynx, trachea, extrapulmonary bronchi, and whole lungs were kept whole for 24 hours. Samples of the trachea (3 levels), the extrapulmonary portion of the 2 main bronchi, and 6 sections of the lung (cranial and caudal left lobes, cranial and middle and caudal right lobes) were then taken for examination. Tissues are processed for histopathology, embedded in paraffin, sectioned at 5 μm, and stained with hematoxylin, eosin, phloxine, and saffron. Slides can be read in a blinded fashion by a board-certified veterinary pathologist.