Table 1.

Synovial fluid results in joint diseases of the dog and cat

										Differential (%)
Condition	Volume (mL)	Color	Clarity	Viscosity	Total protein (g/dL)	Mucin clot	TNCC (cells/μL)	Mono	Neut	Comments	Reference
Normal	0.24	Colorless to straw	Clear	High	<2.5	Good	≤3000	≥90	<10		[32]
Noninflammatory
Degenerative joint disease	N to ↑	Colorless to yellow	Clear	N to ↓	<2.5	Good to fair	≤5000	≥90	<10	Macrophages may be vacuolated	[44]
Trauma	N to ↑	Colorless, yellow bloody	Clear to hazy	↓	NR	Good	2500–3000	≥90	<10	Neutrophil numbers depend on amount of hemorrhage present	[33]
Inflammatory
Infectious
Bacterial (rods/cocci)	N to ↑	Yellow, bloody, or yellowish green	Cloudy to opaque	↓	>2.5	Fair to very poor	15,000– 267,000	5–23	77–95	Neutrophils may be degenerate or nondegenerate; bacteria may be seen in neutrophils	[2], [33], [44]
Borellia burgdorferi (Lyme)	N to ↑	Yellow to bloody	Cloudy	↓	>2.5	Fair to poor	46,300 (mean)	15 (mean %)	85	Spirochetes rarely seen in synovial fluid by dark field microscopy	[14]
Ehrlichia sp	N to ↑	Yellow to bloody	Cloudy	↓	>2.5	Fair to poor	38,800–50,000	20–40	60–80	Ehrlichia morulae may be found in a small percentage of neutrophils	[12], [13]
Mycoplasma sp	N to ↑	Yellow to bloody	Cloudy	↓	>2.5	Fair to poor	Increased	Lymphocytic or neutrophilic		Requires special culture techniques	[15]
Immune mediated
Idiopathic polyarthritis	N to ↑	Yellow to bloody	Hazy to cloud	↓	>2.5	Fair to poor	Increased	≤10	>90		[6]
Systemic lupus erythematosus	N to ↑	Yellow to bloody	Hazy to cloudy	↓	>2.5	Good to poor	6200–371,000	7–85	15–93	May see lupus erythematosus cell, ragocytes, Tart cells; ± ANA-positive	[5]
Canine rheumatoid arthritis	N to ↑	Yellow to bloody	Hazy to cloudy	↓	>2.5	Fair to poor	2900–38,800	Mononuclear or neutrophilic		May see ragocytes: ± RF - positive;	[31]
Feline progressive polyarthritis	N to ↑	Yellow to bloody	Hazy to cloudy	↓	>2.5	Poor	4000–70,000	1–75	25–99	Erosive or proliferative forms	[19], [48]
Lymphoplasmacytic polyarthritis	N to ↑	Yellow	Hazy to cloudy	↓	>2.5	NR	5000–20,000	Mostly lymphocytic		Causes stifle laxity; often mistaken for cranial cruciate rupture	[25]

Abbreviations: ANA, antinuclear antibodies; Mono, mononuclear cells; N, normal; Neut, neutrophils; NR, not reported; RF, rheumatoid factor; TNCC, total nucleated cell count; ↑, increased; ↓, decreased.