# Cytology of the Respiratory Tract: Collection and Interpretation


## Key Takeaways

- Respiratory cytology is a direct diagnostic tool for upper and lower airway diseases in dogs, cats, horses, and cattle, with sample type selection (nasal swabs, tracheal washes, bronchoalveolar lavage) dictated by the suspected anatomical location of pathology.
- Bronchoalveolar lavage (BAL) is the reference standard for inflammatory airway disease in horses and is crucial for differentiating lower respiratory tract infection from bronchial disease in cats when combined with microbiology.
- Neutrophilic predominance in respiratory cytology suggests bacterial infection, aspiration, or nonseptic inflammation, with elevated BAL neutrophil proportions in horses defining inflammatory airway disease when clinical signs are present.
- Macrophage patterns in BAL are significant, particularly for intracellular organisms like Cryptococcus neoformans in immunosuppressed cats, and the presence of neutrophil extracellular traps (NETs) can contribute to airway obstruction in viral diseases.
- Quality assurance, including adherence to ASVCP guidelines for staining, reference intervals, and reporting, is paramount for accurate interpretation, and ancillary testing such as culture and antigen testing complements cytologic findings.
- Distinguishing true infection from contamination in tracheal washes requires correlating cytologic findings (e.g., intracellular bacteria with inflammation) with quantitative culture results and clinical presentation, as low-level oropharyngeal contamination is common.

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Respiratory cytology is a direct window into airway inflammation, infection, and neoplasia. This article covers the collection and interpretation of nasal swabs and flushes, tracheal washes, and bronchoalveolar lavage in dogs, cats, horses, and cattle. It serves the practicing veterinarian who needs a practical framework for choosing a sampling method, handling the sample correctly, and reading the resulting cytology with confidence. The procedural emphasis assumes the reader can perform routine physical examination and basic endoscopic techniques.

The clinical questions answered here are concrete. Which sample type answers which question? How do you distinguish a contaminated tracheal wash from a true lower airway infection? When does a BAL neutrophil proportion change a treatment plan? What does a yeast-laden macrophage mean in an immunosuppressed cat? Each question is addressed with reference to published evidence and established laboratory standards.

## At a Glance

| Parameter | Decision or Fact | Source Context |
|---|---|---|
| Sample type selection | Nasal cytology for upper tract signs, tracheal wash for tracheobronchial disease, BAL for alveolar and small airway disease | MSD Veterinary Manual |
| BAL neutrophil threshold in horses | Elevated proportions define inflammatory airway disease when clinical signs are present | Equine impulse oscillometry study |
| Feline BAL interpretation | Cytology and microbiology together classify lower respiratory tract infection versus bronchial disease | Feline BAL retrospective study |
| Cattle BAL cytology | Neutrophil counts distinguish clinical pneumonia from upper respiratory infection and healthy calves | Calf BAL bacteriology and cytology study |
| NETs in airway cytology | DNA-rich extracellular traps contribute to airway obstruction in viral disease | RSV NET study |
| Quality assurance | Laboratory standards govern staining, reference intervals, and cytology reporting | ASVCP guidelines |
| Ancillary testing | Breath condensate H2O2 correlates with airway inflammation but is not a routine cytology substitute | Equine breath condensate study |

## Why Sample Type Determines Interpretation

The respiratory tract is a continuous epithelial surface with regional differences in cell populations, microbial exposure, and inflammatory responses. A nasal swab samples the stratified squamous and respiratory epithelium of the rostral cavity. A tracheal wash collects mucus and cells from the conducting airways. A bronchoalveolar lavage samples the alveolar spaces and terminal bronchioles. These compartments respond differently to the same disease process, so the reference intervals and interpretive thresholds for one sample type do not transfer to another.

The cellular composition of a healthy BAL is dominated by alveolar macrophages, with smaller proportions of lymphocytes, neutrophils, eosinophils, and mast cells. Inflammatory airway disease in horses shifts this balance toward neutrophilia, and the magnitude of that shift correlates with functional impairment measured by impulse oscillometry. Horses classified as affected by BAL cytology showed increased respiratory resistance at low frequencies compared with controls, confirming that cytologic inflammation has measurable physiologic consequences. The same principle applies across species: cytology is not an abstract laboratory value but a proxy for airway function and disease severity.

## Collection Technique and Sample Quality

### Nasal Sampling

Nasal cytology is indicated for sneezing, nasal discharge, and suspected fungal rhinitis. A swab or flush collects epithelial cells, mucus, and any inflammatory or infectious agents. The sample is inherently contaminated by the nasal microbiome, so interpretation must account for resident flora. Cryptococcal organizms, when present, are usually abundant and morphologically distinctive.

### Tracheal Wash

A tracheal wash can be performed percutaneously, through an endotracheal tube, or via endoscopic catheterization. The sample represents the conducting airways and is appropriate for suspected tracheobronchitis or as a screening test for lower airway disease. The volume of saline instilled and the method of aspiration affect cellular yield. Samples with heavy squamous epithelial contamination indicate oropharyngeal admixture and should be interpreted with caution.

### Bronchoalveolar Lavage

BAL samples the alveolar compartment and is the preferred method for evaluating diffuse parenchymal disease, asthma-like conditions, and opportunistic infections. In horses, BAL cytology is the reference standard for classifying inflammatory airway disease. In cats, BAL cytology combined with microbiology distinguishes lower respiratory tract infection from feline bronchial disease, a distinction that changes therapy. In calves, BAL neutrophil counts differentiate clinical pneumonia from subclinical infection and upper respiratory tract disease, supporting targeted antimicrobial decisions.

The volume of lavage fluid, the number of aliquots, and the site of sampling all influence results. A poorly performed BAL that collapses airways or samples only the mainstem bronchus produces cytology that reflects the trachea, not the alveoli. The operator must confirm the catheter is wedged in a distal airway before instilling fluid.

## Cellular Patterns and Their Meaning

### Neutrophilic Inflammation

Neutrophil predominance indicates bacterial infection, aspiration, or nonseptic inflammatory airway disease. The distinction requires integration of clinical signs, culture results, and the presence of degenerative change. In horses, BAL neutrophil proportions above the reference threshold define inflammatory airway disease when clinical signs are present. In calves, neutrophil counts in BAL fluid are higher in clinical pneumonia than in subclinical pneumonia, upper respiratory infection, or healthy animals.

### Eosinophilic Inflammation

Eosinophil predominance suggests parasitic migration, hypersensitivity, or eosinophilic bronchopneumopathy. The clinical context matters: a horse with summer pasture-associated obstructive pulmonary disease and a cat with suspected asthma both may show eosinophilia, but the management differs substantially.

### Macrophage Patterns

Alveolar macrophages dominate the healthy BAL. Intracellular organizms are diagnostically significant. Cryptococcus neoformans within macrophages is a classic finding in feline pulmonary cryptococcosis, and the narrow-necked budding yeast is morphologically distinctive. Parasitic ova and larvae may also appear within or adjacent to macrophages.

### Neutrophil Extracellular Traps

Activated neutrophils release extracellular networks of DNA and antimicrobial proteins. These structures, called NETs, can trap pathogens but also contribute to airway obstruction. In respiratory syncytial virus disease, NETs have been visualized in lung cytology and tissue samples from affected infants and calves, where they form DNA-rich mucus plugs. Recognizing NETs as a cytologic finding, instead of dismissing them as mucus debris, matters in viral lower respiratory tract disease.

## Ancillary Testing and Quality Assurance

Cytology does not stand alone. Culture, antigen testing, and molecular diagnostics complement the cellular picture. In cats, BAL cytology and microbiology together provide the diagnostic classification. In calves, bacteriology and cytology are compared against clinical scoring and lung ultrasonography to define disease categories.

Laboratory quality standards govern staining methods, reference intervals, and reporting practices. The American Society for Veterinary Clinical Pathology publishes guidelines for quality assurance in veterinary clinical pathology, and the practicing veterinarian should expect cytology reports to conform to these standards. Reference intervals must be appropriate for the species, the sample type, and the laboratory's methods.

Breath condensate analysis remains a research tool. Hydrogen peroxide concentration in expired breath condensate correlates with BAL neutrophil counts and tracheal wash inflammation scores in horses, but this technique is not yet a clinical substitute for cytology.

## Diagnostic Sequence and Decision Points

The order of sample collection follows a deliberate logic. Nasal sampling addresses the upper airway, tracheal wash targets the conducting airways, and bronchoalveolar lavage samples the distal airspaces. When lower respiratory disease is suspected, tracheal wash and BAL are complementary instead of interchangeable. Tracheal wash cytology reflects large airway inflammation and is technically simpler, but it overrepresents neutrophils from tracheal mucus and underrepresents alveolar pathology. BAL samples a defined lung segment and provides the most accurate picture of parenchymal and small airway inflammation.

The decision to progress from one technique to the next depends on the clinical question. A horse with exercise intolerance and a normal tracheal wash may still have inflammatory airway disease detectable only by BAL. In that species, [impulse oscillometry can detect subclinical airway disease when BAL cytology defines the disease group](https://pubmed.ncbi.nlm.nih.gov/19562901/), which supports using BAL as the reference standard when functional testing suggests airway disease. In cats, BAL cytology and microbiology together frequently change the diagnosis, particularly when bronchial disease, infection, and neoplasia are in the differential list. A [retrospective analysis of feline BAL samples](https://pubmed.ncbi.nlm.nih.gov/15135356/) found that cytology and culture identified infectious agents including Mycoplasma spp., Pasteurella spp., and Cryptococcus neoformans, and that the combined results were necessary to classify cases as lower respiratory infection, bronchial disease, or neoplasia.

The decision to culture a sample should be made before collection. Quantitative culture is preferred for BAL because low-level oropharyngeal contamination is common. In calves, [BAL fluid bacteriology and cytology differ between healthy animals and those with subclinical or clinical pneumonia](https://pubmed.ncbi.nlm.nih.gov/32014683/), with higher bacterial counts and neutrophil proportions in pneumonic calves. This supports the use of quantitative thresholds instead of presence or absence of growth. A pure growth of a respiratory pathogen at high concentration is meaningful, mixed growth of multiple organizms at low concentration usually represents contamination.

## Equipment and Consumable Selection

Sample quality depends more on technique than on the specific catheter or syringe used, but equipment choices do matter.

| Technique | Preferred Equipment | Selection Criteria | Common Failure Mode |
|---|---|---|---|
| Nasal flush | Sterile catheter, syringe, collection cup | Suspected fungal rhinitis or foreign body, mass lesions | Sample diluted by saline, low cellularity |
| Tracheal wash | Sterile catheter through endotracheal tube or transtracheal needle | Large airway disease, poor patient tolerance of BAL | Oropharyngeal contamination if catheter contacts the tube |
| Bronchoalveolar lavage | Wedged catheter or bronchoscope with balloon | Small airway or parenchymal disease, research-grade cytology | Inadequate wedge, alveolar sample diluted by airway fluid |

The volume of lavage fluid varies with body size and technique. A general principle is to use the smallest volume that reliably returns alveolar material. For BAL, the recovered fluid should contain a visible pellet after centrifugation. If the pellet is absent or the fluid is clear and watery, the sample is likely diluted airway fluid instead of alveolar lavage. The first aliquot retrieved from a BAL is often bronchial in origin and may be processed separately if the clinical question concerns large airway disease.

## Monitoring Parameters and Sample Quality Checks

Cellularity and cell viability should be assessed before detailed cytologic interpretation. A sample with heavy blood contamination is difficult to interpret because peripheral blood neutrophils and lymphocytes obscure the resident population. A sample with abundant squamous epithelial cells indicates oropharyngeal contamination, and the cytologic findings should be interpreted with caution.

The following parameters should be recorded for every sample:

| Parameter | What It Detects | Action Threshold |
|---|---|---|
| Total nucleated cell count | Overall inflammation | Compare with species and site reference intervals |
| Squamous epithelial cells | Oropharyngeal contamination | If numerous, interpret with caution |
| Ciliated epithelial cells | Bronchial origin | Expected in tracheal wash, less in BAL |
| Red blood cells | Hemorrhage or traumatic collection | If numerous, note and interpret with caution |
| Extracellular mucus | Airway inflammation | Semiquantitative score |
| Cell viability | Sample handling quality | Low viability suggests delayed processing |

Reference intervals differ by species, site, and laboratory. The [ASVCP quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) emphasize that each laboratory should establish or validate reference intervals for the species and sample types it processes. A neutrophil proportion that is normal for a tracheal wash may be abnormal for a BAL, and a cell count that is normal for a horse may be elevated for a cat.

## Documentation and Reporting

Cytologic reports should include the sample site, collection method, volume recovered, total nucleated cell count, and a differential count of at least 200 cells. The report should describe the predominant cell type, the presence of mucus, the presence of infectious agents, and any atypical cells. A semiquantitative mucus score is useful for serial comparisons in horses with recurrent airway obstruction, where [breath condensate hydrogen peroxide correlates with both airway cytology and epithelial lining fluid ascorbic acid concentration](https://pubmed.ncbi.nlm.nih.gov/15104214/), suggesting that oxidative stress markers may track inflammation severity.

The report should distinguish between findings that are diagnostic and findings that are supportive. A narrow-necked, capsulate budding yeast within macrophages is diagnostic for cryptococcosis, as described in a [case of pulmonary cryptococcosis in an FIV-positive cat](https://pubmed.ncbi.nlm.nih.gov/10860150/). In contrast, a predominance of neutrophils is supportive of bacterial infection but not diagnostic, because nonseptic inflammation produces the same pattern.

## Species-Specific Adjustments

The correct technique and interpretation vary by species. In horses, tracheal wash and BAL are both routine, and BAL is the reference standard for inflammatory airway disease. In cattle, BAL is performed through a blind catheter and is used to support a clinical diagnosis of pneumonia, with [combined clinical scoring and lung ultrasonography used to classify calves before sampling](https://pubmed.ncbi.nlm.nih.gov/32014683/). In cats, BAL requires general anesthesia and a smaller volume of lavage fluid, and the sample is often submitted for both cytology and culture because infection and inflammation frequently coexist. In dogs, transtracheal wash is more common than BAL for suspected bacterial bronchitis, but BAL is preferred when interstitial or alveolar disease is suspected.

Patient status changes the risk profile. A patient with respiratory distress may not tolerate BAL under general anesthesia, and a tracheal wash under sedation is a safer alternative. A coagulopathic patient should not undergo transtracheal wash. A patient with a nasal mass may bleed heavily during nasal flush, and the procedure should be performed with the head lowered and the airway protected.

Production systems change what is feasible. On-farm sampling in calves requires portable equipment and rapid processing, and the [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) provide context for disease surveillance and reporting in production animals. In a referral hospital, the full range of techniques is available, and the choice is driven by the clinical question instead of by equipment constraints.

## Complications and Failure Modes

Respiratory sampling is generally low risk, but complications occur and must be recognized promptly. Transient coughing, hemorrhage, and worsening dyspnoea are the most common adverse events after tracheal wash or bronchoalveolar lavage. Coughing usually resolves within minutes and requires no intervention. Hemorrhage is typically mild and self-limiting, but persistent blood in the recovered fluid should be recorded because it compromises cytological interpretation. Severe dyspnoea after bronchoalveolar lavage is uncommon but has been reported in cats with pre-existing airway disease, and oxygen supplementation should be available before the procedure begins.

Nasal sampling carries distinct risks. Hemorrhage from the nasal mucosa can obscure cellular detail, and excessive flushing may force material into the lower airways. In brachycephalic breeds, the narrow nasal passages increase the risk of trauma and iatrogenic obstruction from swelling. Pneumothorax is a rare but serious complication of transtracheal wash when the catheter is advanced too forcefully or the needle is placed incorrectly. Detection relies on post-procedural monitoring for progressive tachypnoea, muffled heart sounds, or sudden deterioration, with thoracic imaging used to confirm the diagnosis.

Vasovagal events, including bradycardia and syncope, can occur during nasal sampling in dogs. These events are usually transient and respond to stopping the procedure and allowing the patient to recover. Sedation protocols should account for the patient's cardiovascular status, and prolonged procedures should be avoided in animals with known cardiac disease.

## Common Errors and Corrective Action

Less experienced clinicians frequently misinterpret sample quality before considering cellular content. A bronchoalveolar lavage sample with heavy blood contamination is often read as hemorrhage instead of as a poorly collected sample that may still contain diagnostic cells. The corrective action is to assess the sample for the presence of alveolar macrophages and ciliated epithelial cells before rendering an interpretation. If these cells are absent, the sample represents upper airway contamination and should not be used to characterize lower airway disease.

Another common error is overinterpreting a single cell type. A mild increase in neutrophils in a tracheal wash may reflect contamination from the upper airway instead of lower airway inflammation. The same finding in a bronchoalveolar lavage sample carries more weight because the sample originates from the alveolar space. Clinicians should correlate cytological findings with the sample type and the clinical presentation before committing to a diagnosis.

Failure to submit samples for culture when infection is suspected is a recurring mistake. Cytology can identify suppurative inflammation, but it cannot reliably distinguish bacterial from non-bacterial causes. The retrospective feline study by Foster and colleagues demonstrated that bronchoalveolar lavage cytology and microbiology together improved diagnostic classification of lower respiratory tract disease, and the authors emphasized that cytology alone was insufficient for cases where infectious agents were ultimately identified [Foster et al., feline bronchoalveolar lavage cytology and microbiology](https://pubmed.ncbi.nlm.nih.gov/15135356/). Submission of an additional sterile sample for aerobic culture and, where indicated, Mycoplasma culture should be routine.

| Observation | Likely Cause | Discriminating Check |
|---|---|---|
| Blood in recovered fluid | Traumatic sampling or mucosal bleeding | Assess for alveolar macrophages, repeat sampling if heavily blood-contaminated |
| No cells or only epithelial cells | Upper airway contamination | Confirm catheter placement, consider repeat lavage |
| High neutrophil count in tracheal wash | Lower airway inflammation or upper airway contamination | Compare with BAL cytology, correlate with clinical signs |
| Organizms seen but no inflammation | Contaminant or colonisation | Correlate with culture results and clinical status |
| Progressive dyspnoea after procedure | Pneumothorax or bronchospasm | Thoracic auscultation and imaging, administer oxygen |

## Limitations of Current Evidence

The evidence base for respiratory cytology is uneven across species. Equine inflammatory airway disease has been studied extensively, with work by Richard and colleagues showing that impulse oscillometry can detect subclinical alterations in respiratory function that correlate with bronchoalveolar lavage cytology [Richard et al., equine inflammatory airway disease and impulse oscillometry](https://pubmed.ncbi.nlm.nih.gov/19562901/). This level of functional correlation is lacking in small animal and production animal medicine.

Bovine respiratory disease classification relies heavily on combined clinical scoring and ultrasonography, but the relationship between these categories and bronchoalveolar lavage cytology is still being defined. Van Leenen and colleagues compared bacteriology and cytology across healthy calves and calves with upper respiratory tract infection, subclinical pneumonia, and clinical pneumonia, and their findings support the use of quantitative bacterial counts and neutrophil percentages to distinguish these groups [van Leenen et al., bovine bronchoalveolar lavage bacteriology and cytology](https://pubmed.ncbi.nlm.nih.gov/32014683/). However, the optimal thresholds for these parameters remain debated, and regional differences in pathogen prevalence limit the generalizability of any single cut-off.

Expert opinion still differs on the clinical significance of neutrophil extracellular traps in airway cytology. Cortjens and colleagues demonstrated that NETs contribute to airway obstruction in respiratory syncytial virus disease in children and calves, and their presence can be visualized in lung cytology using DNA and immunostaining techniques [Cortjens et al., neutrophil extracellular traps in respiratory syncytial virus disease](https://pubmed.ncbi.nlm.nih.gov/26468056/). Whether NETs represent a therapeutic target or simply a marker of severe inflammation is unresolved, and routine cytology does not currently distinguish NETs from other DNA-rich debris.

## Referral and Escalation Criteria

Referral to a specialist is warranted when sampling has failed repeatedly, when the patient is unstable and cannot tolerate further procedures, or when the cytological findings are ambiguous despite adequate sample quality. Cases where the differential diagnosis includes neoplasia, fungal infection, or parasitic disease may benefit from specialist evaluation, particularly when advanced imaging or bronchoscopy is required to obtain targeted samples.

Laboratory involvement should be sought when the sample is unusual, when cell counts are needed for quantitative interpretation, or when specialised staining is required. The American Society for Veterinary Clinical Pathology provides quality assurance guidance for laboratory standards, including reference intervals and method validation, and clinicians should confirm that their laboratory adheres to these standards before relying on quantitative results [ASVCP quality assurance and laboratory standards](https://www.asvcp.org/page/QALS_Guidelines).

Regulatory reporting is required when a notifiable pathogen is identified or suspected. The World Organization for Animal Health maintains the terrestrial animal health code, which lists reportable diseases and provides standards for surveillance and trade-related disease control [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). Clinicians should be familiar with the reporting requirements in their jurisdiction and should contact the relevant authority promptly when a listed disease is suspected.

## Frequently Asked Questions

### How Should I Prioritize Respiratory Cytology When the Owner Has a Limited Budget?

Start with a tracheal wash or blind BAL before advanced imaging. These samples provide the highest diagnostic yield per cost for diffuse lower airway disease. If the primary concern is nasal disease, a nasal flush or swab cytology is inexpensive and can be performed in most consultations. Reserve bronchoscopy for cases where focal lesions are suspected or where blind sampling has failed. When funds are limited, request a Diff-Quik stain and a Gram stain, and ask the laboratory to hold the sample for possible culture if cytology suggests sepsis. The [ASVCP quality assurance guidelines](https://www.asvcp.org/page/QALS_Guidelines) provide a framework for deciding which stains and preparations are essential versus optional.

### What Can I Do When Bronchoscopy Is Unavailable?

Blind BAL using a cuffed endotracheal tube or a commercially available BAL catheter is a reliable alternative. In dogs and cats, pass the catheter to the level of the distal trachea, inflate the cuff, and instill warmed sterile saline. In horses, a long guarded catheter passed through the nasal passage works well. The main limitation is that you cannot visually target a lesion, so sensitivity for focal disease drops. For diffuse disease, blind BAL cytology correlates well with bronchoscopic sampling. In calves, blind BAL is standard practice and can be combined with lung ultrasonography to improve case selection, as described in [comparative studies of BAL fluid bacteriology and cytology in calves](https://pubmed.ncbi.nlm.nih.gov/32014683/).

### How Do I Distinguish True Infection from Contamination in a Tracheal Wash?

The upper airway normally harbors low numbers of commensal bacteria, so a positive culture alone is not diagnostic. Interpret cytology and culture together. Neutrophilic inflammation with intracellular bacteria supports true infection. Extracellular bacteria with a mixed population and minimal inflammation suggest oropharyngeal contamination. Quantitative culture thresholds help: growth of a single organizm in high numbers is more meaningful than mixed growth of several species. In cats, Mycoplasma spp. and Bordetella bronchiseptica are clinically significant isolates even when inflammation is mild, as shown in [feline BAL cytology and microbiology studies](https://pubmed.ncbi.nlm.nih.gov/15135356/). Always correlate with clinical signs and radiographic findings before committing to antimicrobial therapy.

### What Is the Best Way to Handle a Sample That Is Mostly Mucus or Blood?

Mucus-heavy samples should be treated with a mucolytic agent such as N-acetylcysteine before cytocentrifugation, but this must be done promptly because the agent can alter cell morphology over time. Blood contamination dilutes the cellular population and can mimic inflammation. If the sample is grossly bloody, note the degree of contamination on the submission form and interpret neutrophil counts with caution. A differential count based on 200 nucleated cells is still possible if the blood is not overwhelming. In horses, mucus scoring is itself a diagnostic parameter, and [breath condensate hydrogen peroxide correlates with airway cytology and mucus scores](https://pubmed.ncbi.nlm.nih.gov/15104214/), so a mucus-heavy sample is not wasted even when cellular detail is poor.

### How Should I Document Respiratory Cytology Findings in the Medical Record?

Record the sampling method, the volume of fluid instilled and retrieved, the gross appearance, and the cellular differential count. Include a description of cell morphology, presence of intracellular or extracellular bacteria, and any infectious agents such as fungal organizms or parasitic larvae. Note the sample quality and any limitations such as blood contamination or low cellularity. State your cytologic interpretation and how it integrates with other diagnostics. The [AVMA practice resources](https://www.avma.org/resources-tools) emphasize that medical records must support clinical reasoning and follow-up decisions. If the sample was sent to an external laboratory, attach the report and document how the findings influenced the treatment plan.

### How Do I Explain a Nondiagnostic or Conflicting Cytology Result to the Owner?

Be direct about what the sample did and did not show. Explain that a negative or nondiagnostic result does not rule out disease, and that repeat sampling or additional tests may be needed. For example, a BAL with low cellularity in a coughing cat does not exclude feline bronchial disease, it may reflect sampling error or a patchy disease process. In horses with inflammatory airway disease, cytologic abnormalities can be present even when the horse appears clinically normal, so a normal-looking horse can still have a meaningful result, as demonstrated in [impulse oscillometry studies of subclinical inflammatory airway disease](https://pubmed.ncbi.nlm.nih.gov/19562901/). Frame the discussion around the next diagnostic step instead of the failed test, and be honest about the limitations of cytology in reaching a definitive diagnosis.

## Related Clinical & Scientific Guides

* [Peripheral Blood Smear Evaluation: A Step-by-Step Guide](/knowledge/veterinary-medicine/clinical-pathology/peripheral-blood-smear-evaluation-guide)
* [Reticulocyte Counts in Veterinary Medicine: Clinical Utility and Interpretation](/knowledge/veterinary-medicine/clinical-pathology/reticulocyte-counts-veterinary-medicine)
* [Cerebrospinal Fluid Analysis in Veterinary Neurology: Collection and Interpretation](/knowledge/veterinary-medicine/clinical-pathology/cerebrospinal-fluid-analysis-veterinary)


## References and Further Reading

- [Breath condensate hydrogen peroxide correlates with both airway cytology and epithelial lining fluid ascorbic acid concentration in the horse.](https://pubmed.ncbi.nlm.nih.gov/15104214/). 2004.
- [Neutrophil extracellular traps cause airway obstruction during respiratory syncytial virus disease.](https://pubmed.ncbi.nlm.nih.gov/26468056/). 2016.
- [A retrospective analysis of feline bronchoalveolar lavage cytology and microbiology (1995-2000).](https://pubmed.ncbi.nlm.nih.gov/15135356/). 2004.
- [Influence of subclinical inflammatory airway disease on equine respiratory function evaluated by impulse oscillometry.](https://pubmed.ncbi.nlm.nih.gov/19562901/). 2009.
- [Pulmonary cryptococcosis and Capillaria aerophila infection in an FIV-positive cat.](https://pubmed.ncbi.nlm.nih.gov/10860150/). 2000.
- [Comparison of bronchoalveolar lavage fluid bacteriology and cytology in calves classified based on combined clinical scoring and lung ultrasonography.](https://pubmed.ncbi.nlm.nih.gov/32014683/). 2020.
- [American Society for Veterinary Clinical Pathology Guidelines](https://www.asvcp.org/page/QALS_Guidelines). American Society for Veterinary Clinical Pathology.
- [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual.
- [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association.

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> This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.