# Cytology of Joint Fluid: Collection and Interpretation in Arthropathies


## Key Takeaways

- Synovial fluid cytology is critical for differentiating non-inflammatory (e.g., osteoarthritis) from inflammatory arthropathies, with normal fluid exhibiting low nucleated cell counts (<1,500 cells/µL) and mononuclear predominance.
- A neutrophil predominance (>10% of nucleated cells) strongly suggests inflammatory arthropathy, with degenerate neutrophils and intracellular bacteria being highly indicative of septic arthritis, though culture remains essential for definitive diagnosis.
- Septic arthritis requires prompt antimicrobial therapy and potentially surgical lavage; however, culture yields are often low (<50% positive), making rapid cytologic assessment crucial for initiating treatment.
- Immune-mediated polyarthritis (IMPA) typically presents with neutrophilic pleocytosis (5,000-50,000 cells/µL) and moderately elevated protein, distinct from the more severe degeneration and higher cell counts seen in sepsis.
- Arthrocentesis technique requires strict aseptic protocols, appropriate needle selection (22-gauge for small animals, 18-20-gauge for large animals), and sample collection into EDTA for cytology and plain tubes for culture.
- Contraindications for arthrocentesis include coagulopathies, overlying cellulitis, and unstable fractures, while complications like iatrogenic hemorrhage can be mitigated by careful technique and sample assessment.

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Joint fluid cytology is a core diagnostic procedure in the evaluation of lameness and joint disease across companion animal and equine practice. This article provides a structured approach to arthrocentesis, sample handling, cytologic interpretation, and classification of arthropathies for the practicing veterinarian. It addresses the procedural decisions that determine sample quality, the cellular patterns that distinguish degenerative from inflammatory and septic joint disease, and the limitations of cytology when used alone. The content is intended for clinicians who perform joint taps in dogs, cats, and horses and who integrate cytologic findings with imaging, synovial fluid biochemistry, and microbiology.

## At a Glance

| Parameter | Key Information |
|---|---|
| Sample volume | 0.5 to 2 mL typically sufficient, smaller volumes still permit smear preparation |
| Anticoagulant | EDTA preferred for cell counts and morphology, plain tube for culture |
| Normal nucleated cell count | Low, species-dependent, predominantly mononuclear cells |
| Neutrophil predominance | Suggests inflammatory arthropathy, septic unless proven otherwise |
| Degenerate neutrophils | Strongly supportive of sepsis, but absence does not exclude infection |
| Culture yield in septic arthritis | Positive in a minority of cases, cytology remains the faster diagnostic |
| Repeated arthrocentesis | Does not induce neutrophilic inflammation in healthy dogs at 3-week intervals |
| Contraindications | Coagulopathy, overlying cellulitis, unstable fracture |

## Physiology of Synovial Fluid

Synovial fluid is an ultrafiltrate of plasma modified by hyaluronan secretion from synoviocytes lining the joint capsule. The synovial membrane lacks a basement membrane, which permits selective passage of small molecules while large proteins are largely excluded. This explains why normal joint fluid has low total protein and a sparse cellular population. The predominant resident cells are mononuclear, comprising synovial lining cells, macrophages, and small lymphocytes. Neutrophils are normally absent or present in very low numbers.

The synovial membrane responds to injury and inflammation in a stereotyped manner. Vascular permeability increases, protein content rises, and leukocytes migrate into the joint space. The magnitude and character of this cellular response correlate with the underlying disease process. Degenerative arthropathies produce mild mononuclear-predominant effusions, whereas immune-mediated and septic arthritides generate intense neutrophilic responses. Understanding this physiology allows the clinician to interpret cytologic findings within a mechanistic framework instead of as isolated cell counts.

## Arthrocentesis Technique

### Patient Preparation and Positioning

Arthrocentesis requires aseptic technique. Clip the hair over the joint, perform a surgical scrub, and wear sterile gloves. Sedation is often necessary in dogs and cats, and standing sedation with regional analgesia is standard in horses. The joint should be positioned to open the joint space maximally. For the carpus, flex the joint, for the stifle, place the limb in a semi-flexed position with the patella centered. The clinician must know the arthrocentesis approach for each joint before attempting the procedure, as needle placement into periarticular fat or tendon yields misleading samples.

### Needle Selection and Collection

Use a 22-gauge needle for most dogs and cats, and an 18- or 20-gauge needle for horses and large dogs. A 1 to 3 mL syringe is adequate. Insert the needle with a single smooth motion, and aspirate gently. If no fluid appears, rotate the needle or redirect slightly without withdrawing completely. Synovial fluid may be viscous, so slow, steady aspiration is more effective than forceful pulling. Collect fluid into an EDTA tube for cytology and cell counts, and into a plain sterile tube for bacterial culture when sepsis is suspected. If only a drop of fluid is obtained, expel it directly onto a glass slide and make a smear immediately.

### Complications and Limitations

Hemorrhage during arthrocentesis is the most common complication. Blood contamination dilutes the sample and can be mistaken for inflammatory change if the clinician does not account for peripheral blood cells. Repeated attempts increase the risk of iatrogenic hemorrhage and introduce bacteria. In healthy dogs, repeated arthrocentesis at 3-week intervals does not induce neutrophilic inflammation, although mild mononuclear inflammation occurs occasionally, supporting the safety of serial sampling for treatment monitoring in immune-mediated polyarthritis. Contraindications include coagulopathies, cellulitis overlying the joint, and unstable fractures involving the joint.

## Sample Handling and Laboratory Submission

### Anticoagulant Choice

EDTA is the preferred anticoagulant for synovial fluid cytology because it preserves cell morphology and prevents clotting. Heparin can cause clumping and poor smear quality. If the sample is visibly clotted, it is unsuitable for accurate cell counts, though a smear may still provide useful morphologic information. Submit the EDTA sample chilled if transport exceeds a few hours. For culture, inoculate blood culture medium at the time of collection when possible, as synovial fluid itself supports bacterial growth poorly and culture yield declines with delay.

### Smear Preparation

Prepare smears from fresh fluid within 30 minutes of collection. A direct smear works well for inflammatory fluids with high cell counts. For low-cellularity fluids, cytocentrifugation concentrates cells and improves diagnostic yield. Air-dry smears and stain with a Romanowsky-type stain. Cell counts can be performed manually with a hemocytometer or by automated analyzers validated for synovial fluid, though viscosity may interfere with automated methods. Total protein is measured by refractometry on supernatant after centrifugation.

## Classification of Arthropathies

Arthropathies are classified cytologically into noninflammatory and inflammatory categories. Noninflammatory joint disease, including osteoarthritis and traumatic arthropathy, typically yields fluid with low nucleated cell counts and mononuclear predominance. Inflammatory arthropathies are subdivided into septic and nonseptic categories based on the presence of neutrophils, bacterial organizms, and degenerate cell morphology. This binary classification guides immediate clinical decisions, particularly the need for antimicrobial therapy and surgical intervention. The distinction is not always absolute, as chronic septic arthritis can present with mixed cellularity and pre-existing osteoarthritis may complicate interpretation.

## Diagnostic Approach to the Arthropathic Joint

The clinical presentation determines how aggressively joint fluid should be pursued. Acute, monoarticular lameness with joint effusion and pain on manipulation warrants arthrocentesis before any anti-inflammatory therapy is administered. Polyarticular stiffness in a dog with fever and leukocytosis supports immune-mediated polyarthritis (IMPA) and requires sampling of multiple joints. Chronic, slowly progressive lameness in an older large-breed dog with radiographic osteophytes may still benefit from fluid analysis to exclude low-grade sepsis, particularly when pre-existing osteoarthritis is present. In one case series of spontaneous septic elbow arthritis in dogs, all affected elbows had pre-existing osteoarthritis, and the acute onset of severe lameness with joint effusion was the dominant clinical signal.

Arthrocentesis should be performed before intra-articular or systemic glucocorticoid administration. Glucocorticoids suppress the cytologic inflammatory response within hours and can render a septic joint falsely reassuring. Antibiotics should likewise be withheld until fluid has been collected, unless the patient is systemically unstable and antimicrobial therapy cannot be delayed. In that situation, collect fluid first, then treat, and interpret cytology with the knowledge that neutrophil numbers may already be declining.

### Joint Selection and Sampling Strategy

The choice of joints to sample depends on the suspected disease category and the species.

| Disease category | Joints to sample | Number of joints | Rationale |
|---|---|---|---|
| Suspect sepsis, monoarticular | The affected joint | 1 | Highest yield, compare to contralateral if effusion is bilateral |
| Suspect IMPA, dog | Carpi, tarsi, stifles | 3 to 5 | IMPA is often asymmetric, sampling multiple joints increases sensitivity |
| Suspect IMPA, cat | Carpi, tarsi, stifles | 3 to 5 | Same rationale as dog, feline IMPA may be paucisymptomatic |
| Suspect osteoarthritis, horse | The most lame limb, fetlock or carpus | 1 to 2 | Confirms non-septic inflammation, supports decision to inject |
| Suspect sepsis, horse | The affected joint | 1 | Culture and cytology guide antimicrobial choice |

In dogs, the carpus is the most accessible joint and yields the largest fluid volume. The tarsus and stifle are acceptable alternatives. In horses, the metacarpophalangeal joint and carpus are commonly sampled under standing sedation with regional or local anesthesia. The clinician should sample the joint that is most likely to yield diagnostic fluid, not necessarily the joint that is most painful, because severe periarticular pain can accompany tenosynovitis or periostitis without true synovial effusion.

Repeated arthrocentesis at three-week intervals in healthy dogs does not induce neutrophilic synovial inflammation, although mild mononuclear inflammation was detected in a small proportion of samples in one prospective study. This supports the use of serial sampling to monitor response to immunosuppressive therapy in IMPA. The clinician should still document each arthrocentesis in the medical record, including the joint sampled, the volume obtained, the gross appearance, and the cytologic findings, because serial comparisons are only meaningful when the sampling technique and laboratory handling are consistent.

### Gross Assessment and Point-of-Care Testing

Synovial fluid is assessed immediately after collection. Normal fluid is clear, colorless to pale yellow, and highly viscous. Viscosity is assessed by allowing a drop to string from the needle hub or by observing the fluid's resistance to aspiration. Normal fluid forms a string of 2 to 3 cm before breaking. Septic and inflammatory fluids are typically watery and do not string. Turbidity correlates with nucleated cell count, frankly purulent fluid is opaque and creamy.

Total protein can be estimated with a refractometer, but synovial fluid contains a mixture of albumin and globulins, and the refractive index overestimates protein compared with serum. A more accurate measurement uses a biochemical analyzer on the fluid supernatant after centrifugation. Normal synovial fluid total protein is below 2.5 g/dL in dogs and horses. Values above 3.0 g/dL indicate increased vascular permeability and support an inflammatory arthropathy. In the equine groove model of osteoarthritis, synovial fluid total protein was significantly elevated without a corresponding increase in nucleated cell count, indicating that protein elevation alone does not distinguish degenerative from inflammatory disease.

A direct smear should be made at the time of collection, before the sample is placed in anticoagulant, because synovial fluid clots rapidly and the clot traps cells. If the fluid is visibly turbid, a direct smear is sufficient. If the fluid is clear, cytocentrifugation or sedimentation improves cellular yield. The smear should be air-dried and stained with a Romanowsky-type stain. A second EDTA tube should be submitted for automated cell counting if the laboratory offers it, but the clinician should be aware that synovial fluid mucin can interfere with impedance-based counters.

### Cytologic Interpretation

The nucleated cell count and differential are the core of synovial fluid interpretation. Normal synovial fluid contains fewer than 1,500 nucleated cells per microliter in dogs and horses, with a predominance of small mononuclear cells, primarily macrophages and synovial lining cells. Neutrophils should comprise less than 10% of the nucleated cell population. The total protein is below 2.5 g/dL.

| Finding | Cell count (cells/µL) | Differential | Protein (g/dL) | Interpretation |
|---|---|---|---|---|
| Normal | < 1,500 | > 90% mononuclear | < 2.5 | No arthropathy |
| Non-inflammatory | 1,500 to 5,000 | Mononuclear predominance | 2.5 to 3.5 | Osteoarthritis, trauma, degenerative joint disease |
| Inflammatory, non-septic | 5,000 to 50,000 | Neutrophils 50% to 90% | 3.0 to 5.0 | IMPA, polyarthritis, immune-mediated disease |
| Inflammatory, septic | > 50,000 | Neutrophils > 90%, degenerate | > 4.0 | Bacterial sepsis, fungal arthritis |
| Hemorrhagic | Variable | Erythrophagocytosis, hematoidin | Variable | Recent trauma, coagulopathy, iatrogenic |

Septic arthritis is characterized by a marked neutrophilic pleocytosis with degenerate neutrophils. Intracellular bacteria may be visible in up to half of canine cases. The absence of visible bacteria does not exclude sepsis. In the canine elbow sepsis series, all cases had increased neutrophil counts on cytology, but culture was positive in only 12 of 21 joints. The clinician should therefore submit fluid for aerobic and anaerobic culture whenever sepsis is suspected, even if organizms are not seen. Culture results should be interpreted alongside cytology, because a negative culture in the face of a marked degenerative neutrophilic response does not rule out infection.

Immune-mediated polyarthritis typically produces a neutrophilic inflammation with fewer degenerate changes than sepsis. The neutrophil count is usually between 5,000 and 50,000 cells per microliter, and the protein is moderately elevated. Lupus erythematosus cells are rarely seen and are not required for diagnosis. The distinction between septic and immune-mediated arthritis rests on the degree of neutrophil degeneration, the presence of intracellular bacteria, and the clinical context. When the cytology is ambiguous, culture results and response to therapy guide the final classification.

Osteoarthritis produces a mild mononuclear inflammation. The nucleated cell count is often within the normal to mildly elevated range, and the differential is dominated by macrophages and small lymphocytes. The presence of chondrocytes or cartilage fragments is uncommon and does not correlate with the severity of cartilage damage. Synovial fluid from osteoarthritic joints may contain increased concentrations of inflammatory mediators, including endocannabinoids and related acylethanolamides, but these are research biomarkers and are not used in routine clinical cytology.

### Documentation and Reporting

The cytology report should include the gross appearance, viscosity, total protein, nucleated cell count, and differential count. The report should describe cell morphology, including the presence of degenerate neutrophils, intracellular bacteria, erythrophagocytosis, and any atypical cells. The clinician should record the joints sampled, the volume obtained from each, and the ease of collection. A dry tap should be documented as such, because it may reflect a normal joint with minimal fluid or a fibrotic joint capsule.

The report should also state the cytologic classification, such as non-inflammatory, inflammatory non-septic, inflammatory septic, or hemorrhagic, and should list the differential diagnoses that fit that classification. The final interpretation integrates cytology with radiography, synovial fluid culture, and serology. Cytology alone rarely provides a definitive etiologic diagnosis, but it reliably narrows the differential list and directs the next diagnostic step.

## Recognized Complications and Failure Modes

Arthrocentesis is a low-morbidity procedure, but complications occur and are often detectable before they become clinically significant. The most common complication is iatrogenic hemorrhage. Blood contamination degrades cytologic interpretation by diluting nucleated cells and introducing peripheral neutrophils and platelets. Detect it early by noting whether the fluid clears during collection. A persistently blood-tinged sample with a concurrent drop in nucleated cell count suggests significant hemorrhage instead of a truly hemorrhagic effusion. Compare the packed cell volume of the fluid with the patient's venous hematocrit, a fluid hematocrit approaching peripheral blood confirms contamination.

Post-arthrocentesis sepsis is rare but catastrophic. It presents as progressive joint swelling, severe pain on manipulation, and systemic signs within 24 to 72 hours. The risk rises with repeated attempts, contaminated preparation, or sampling through infected skin. In dogs with pre-existing elbow osteoarthritis, spontaneous septic arthritis can mimic an acute flare, and cytology may show degenerate neutrophils even when culture is negative, so maintain a low threshold for re-evaluation when clinical signs worsen after sampling.

Repeated arthrocentesis for treatment monitoring carries a small risk of procedure-induced inflammation. In healthy dogs sampled every three weeks, serial arthrocentesis did not increase synovial fluid neutrophil numbers, although mild mononuclear inflammation occurred in a minority of samples. When interpreting serial samples, a rising neutrophil proportion should therefore prompt consideration of worsening disease instead of an artefact of repeated puncture, but a mild mononuclear response can be procedure-related.

Joint swelling or effusion after sampling is usually mild and self-limiting. Marked swelling with heat suggests haemarthrosis or infection. Nerve or vessel injury is uncommon with standard approaches but can occur with excessive needle redirection. Tendon or ligament penetration does not typically cause clinically significant morbidity but can introduce blood into the sample.

## Common Errors and Corrective Actions

Less experienced clinicians most often err in sample handling instead of in needle placement. Using excessive suction during aspiration collapses the synovial villi and produces a dry tap. Applying negative pressure only after the needle enters the joint space, and releasing it before withdrawal, preserves yield. Over-declining the smear is equally common, synovial fluid has low cellularity, and thick smears obscure nuclear detail. Prepare smears immediately and stain promptly, as delayed staining causes artefactual cell degeneration.

Misclassification of cell types is a frequent interpretive error. Synovial lining cells are large, round to polygonal, and often vacuolated, they are easily mistaken for macrophages or neoplastic cells. Clusters of lining cells are normal in mildly inflammatory fluid and should not be reported as suspicious. Conversely, degenerate neutrophils with intracellular bacteria confirm sepsis, but their absence does not exclude it, since culture is positive in only a proportion of cytologically inflammatory joints.

Another common error is over-interpreting the total nucleated cell count without reference to fluid volume and viscosity. A viscous, mucinous sample from a normal joint may have a low cell count, while a watery, non-viscous sample with a modest cell count is more concerning. Always integrate viscosity, color, and mucin clot quality with the cell count instead of relying on any single parameter.

## Limitations of the Evidence and Areas of Expert Disagreement

The evidence base for synovial fluid interpretation is strongest in dogs and horses, with comparatively little published work in cats, ruminants, and exotic species. Reference intervals for synovial fluid nucleated cell counts vary between laboratories and between joints within the same animal, and the American Society for Veterinary Clinical Pathology recommends that each laboratory validate its own reference intervals instead of adopt published values uncritically.

Expert opinion differs on the threshold for diagnosing septic arthritis cytologically. Some clinicians treat any sample with more than 90 percent neutrophils as septic until proven otherwise, while others require degenerate neutrophils or visible bacteria. The canine elbow sepsis literature shows that cytology can be strongly inflammatory yet culture-negative, so the decision to treat should incorporate clinical signs, imaging, and response to therapy instead of cytology alone.

There is also disagreement about the clinical significance of mild mononuclear inflammation in serial samples. The finding that repeated arthrocentesis can induce a mild mononuclear response in healthy dogs has led some specialists to recommend longer intervals between monitoring taps, while others consider the effect clinically negligible. Until larger studies clarify this, interpret mild mononuclear shifts in the context of the patient's overall response.

In horses, experimental osteoarthritis models reliably produce elevated synovial fluid total protein without marked cytologic inflammation, and novel intra-articular therapies can cause mild transient increases in nucleated cell counts and protein. These changes are expected and should not be mistaken for sepsis or treatment failure.

## Escalation and Referral

Referral is warranted when the diagnosis remains uncertain after cytology, when septic arthritis is suspected but culture is negative, or when the patient fails to improve despite appropriate therapy. Specialist input is also appropriate for atypical joints such as the temporomandibular joint or atlanto-occipital joint, where blind arthrocentesis carries higher risk. Laboratory involvement is indicated when polarised light microscopy is needed to identify crystals, when flow cytometry or immunophenotyping is considered for suspected neoplasia, or when the sample is too degenerate for reliable morphologic assessment.

Regulatory reporting is rarely required for joint fluid findings, but it applies when a zoonotic agent such as Brucella canis is isolated or suspected, or when a notifiable disease is on the differential list. Consult the World Organization for Animal Health terrestrial animal health standards for the current list of reportable arthropathies in your region.

## Troubleshooting Guide

| Observation | Likely Cause | Discriminating Check |
|---|---|---|
| Blood-tinged fluid, low nucleated count | Iatrogenic hemorrhage | Compare fluid hematocrit with venous hematocrit |
| Dry tap despite correct landmarks | Excessive suction collapsing villi | Release suction, redirect needle, attempt again |
| Thick smear, poor nuclear detail | Over-declining or delayed staining | Prepare fresh smear, stain immediately |
| Large vacuolated cells in clusters | Synovial lining cells, not neoplasia | Assess nuclear-to-cytoplasmic ratio and cell uniformity |
| High neutrophil proportion, no visible bacteria | Septic arthritis with negative cytology | Submit aerobic and anaerobic culture, reassess clinically |
| Mild mononuclear inflammation on serial tap | Procedure-related inflammation | Correlate with clinical response, consider longer interval |
| Rising protein without cytologic inflammation | Early osteoarthritis or post-injection response | Monitor serially, image the joint |

## Frequently Asked Questions

### How should I interpret synovial fluid results when the total volume collected is very small?

Even a single drop can yield diagnostic information if handled correctly. Expel the fluid directly onto a glass slide and smear it immediately, or rinse the needle and syringe with a small volume of sterile EDTA solution and smear that. Prioritize a stained smear over automated cell counts when volume is limiting, since a manual differential and cell morphology assessment often carry more diagnostic weight than a total nucleated cell count alone. Report the sample as limited-volume and note that nucleated cell counts may underestimate the true value because of dilution or inadequate cellular yield. If cytology shows degenerate neutrophils, treat as suspected sepsis even when culture is not possible.

### What can I do when I cannot obtain a sterile arthrocentesis kit or appropriate needles?

A standard 22 gauge, 1 to 1.5 inch hypodermic needle attached to a 3 mL syringe is adequate for most canine and feline joints, and for equine distal limb joints. Clip and aseptically prepare the site thoroughly, wear sterile gloves, and use a no-touch technique where the needle hub is handled only with sterile gauze. For larger equine joints such as the stifle or shoulder, a 3.5 inch spinal needle is preferable, but a longer regular needle can substitute if the landmark is clear. Do not compromise on skin preparation, as iatrogenic sepsis is the principal avoidable complication. If the sample is contaminated with blood, note this on the submission form and interpret nucleated cell counts cautiously.

### How does the diagnostic approach differ in cattle, sheep, goats, and pigs compared with dogs and cats?

Arthrocentesis in ruminants and pigs follows the same landmarks but often requires heavier sedation or regional anesthesia, and the joints are smaller relative to body mass than in dogs. Septicemic arthritis in neonates and polyarthritis secondary to Mycoplasma species are common differentials in production animals, so culture and PCR are frequently more important than in companion animal practice. Joint fluid from healthy cattle is often more turbid and may contain higher baseline nucleated cell counts than canine fluid. Always consider the herd or flock context, and consult species-specific reference intervals where available. Biosecurity and zoonotic considerations, particularly for Brucella and Streptococcus suis, should influence sample handling and laboratory communication.

### What should I document in the medical record after arthrocentesis?

Record the joints sampled, the volume and gross appearance of fluid from each site, the needle gauge and whether the procedure was performed under sedation or general anesthesia, and any difficulty encountered. Document the number of attempts per joint, since repeated needle passes increase the risk of hemorrhage and iatrogenic inflammation. Note whether the sample was placed in EDTA, whether a direct smear was made at the bedside, and the time between collection and laboratory processing. Include a cytologic description with the estimated nucleated cell count, the differential count, and the presence or absence of degenerate neutrophils, macrophages, or cartilage fragments. Serial arthrocentesis at three-week intervals can be used to monitor treatment response in immune-mediated polyarthritis without inducing neutrophilic inflammation in healthy dogs, but record each procedure independently to track any procedure-related change.

### How should I explain the procedure and its limitations to an owner before sampling?

Explain that arthrocentesis is a minimally invasive procedure performed under sedation or anesthesia, and that the main risks are transient pain, bleeding into the joint, and a small risk of introducing infection. State that the fluid analysis distinguishes inflammatory from non-inflammatory joint disease and helps differentiate immune-mediated from septic arthritis, but that culture is positive in only a proportion of septic cases, so a negative culture does not exclude infection. Mention that results may take several days when culture is requested. If the owner asks about cost, explain that the cytology and culture fees are separate from the procedure fee and that additional tests such as PCR or biomarker assays may be recommended depending on the initial findings.

### When should I refer the case instead of proceed with further diagnostic testing in general practice?

Refer when the joint cannot be sampled safely without advanced imaging, when the patient requires general anesthesia that the practice cannot provide, or when the cytologic findings suggest a process beyond the practice's diagnostic capacity, such as suspected neoplasia requiring immunocytochemistry or flow cytometry. Refer early in suspected septic arthritis when the patient is systemically unwell, since delayed surgical lavage worsens outcome. In dogs with pre-existing osteoarthritis and acute lameness, septic arthritis should be considered a major differential even without pyrexia, and referral for joint exploration may be indicated if cytology is equivocal. If the owner declines referral, document the discussion and the recommended monitoring plan.

## 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

- [Effect of repeated arthrocentesis on cytologic analysis of synovial fluid in dogs.](https://pubmed.ncbi.nlm.nih.gov/19566847/). 2009.
- [Spontaneous Septic Arthritis of Canine Elbows: Twenty-One Cases.](https://pubmed.ncbi.nlm.nih.gov/30300912/). 2018.
- [The use of equine chondrogenic-induced mesenchymal stem cells as a treatment for osteoarthritis: A randomised, double-blinded, placebo-controlled proof-of-concept study.](https://pubmed.ncbi.nlm.nih.gov/30815897/). 2019.
- [Evaluating the Safety of Intra-Articular Mitotherapy in the Equine Model: A Potential Novel Treatment for Osteoarthritis.](https://pubmed.ncbi.nlm.nih.gov/36384191/). 2023.
- [Characterization of endocannabinoids and related acylethanolamides in the synovial fluid of dogs with osteoarthritis: a pilot study.](https://pubmed.ncbi.nlm.nih.gov/29110674/). 2017.
- [Development of an equine groove model to induce metacarpophalangeal osteoarthritis: a pilot study on 6 horses.](https://pubmed.ncbi.nlm.nih.gov/25680102/). 2015.
- [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.