The gold standard for diagnosis is fungal culture with dermatophyte test medium preferred, and identification of the characteristic macroconidia using lactophenol blue stain. This method takes about 1 week and so is costly of both time and labor. Although examination of hairs with a Wood's lamp is much easier, not all strains of dermatophytes fluoresce and only about 50% of M. canis strains fluoresce. An easy, reliable and time saving microscopic method is to examine skin scrapings of the lesion with Wright-Giemsa or other cytologic stain. Arthrospores of dermatophytes can be readily visualized along the hair shaft. A #10 scalpel blade is used to obtain a skin scraping of sufficient depth to cause some bleeding and taken in the direction of the hair growth. The material is spread on a clean slide and allowed to air dry. The serum proteins dried on the slide help affix the hair shafts to prevent them being washed off during staining and rinsing. While the type of dermatophyte is not identified here, the speed of diagnosis permits earlier treatment.

Mycoplasma spp. are normal flora of the upper airway (above the larynx), but are not believed to colonize the lower airway (trachea and lungs). However, Mycoplasma spp. have been isolated alone and in combination with other bacteria from lungs of dogs and cats with pulmonary disease. A recent study examined 272 cases of small animal lower airway disease. Of these, 224 (82%) had samples for Mycoplasma spp. and aerobic bacteria culture collected by transtracheal aspiration, transoral airway washing, or bronchoalveolar lavage. About half (113 cases) were negative for Mycoplasma spp., while the remaining 111 cases were Mycoplasma spp. positive alone (17) or in combination with one or more aerobic bacteria (94 cases, 85%). Primary diagnoses were pneumonia, airway collapse, and bronchitis, in approximately equal numbers. Of 14 cases with followup data available, eight resolved or improved with antimycoplasmal drugs.

This study emphasizes the importance of airway washings and culture (aerobic and mycoplasmal) in cases that are poorly responsive to empirical treatment.