Synonym
Tubes
10-15 mL of synovial fluid, typically collected in 4-5 tubes
- Lavender top tube (2 mL; for cell count and differential)
- Sterile container or special vials (2-5 mL; for microbiology, Gram stain, and AFB stain; if possible, inoculate medium immediately)
- Green top tube (5 mL; crystal examination, protein, glucose, lactic acid, and pH)
- Red or tiger top tube (2 mL; for general appearance, clot evaluation, antinuclear antibodies, complement, rheumatoid factor, and uric acid)
- Clear container with fixative (5 mL; for cytology)
If indicated; may also consider drawing blood cultures and 5-10 mL of venous blood in red or tiger top tube (for total protein, glucose, uric acid, or others testing as indicated)
Synovial fluid aspiration procedure (diagnostic arthrocentesis)
- The optimum site for aspiration of many joint is the anterior aspect of most extremity joints except wrist, elbow, and digits for which a posterior approach is preferred
- Position the patient, sterilized the skin with chlorhexidine or betadine
- Administer local anesthetic (1% lidocaine)
- Insert a 18-20 gauge needle attached to a 20-30 mL syringe into the joint space and aspirate synovial fluid (goal is a minimum of 10-15 mL)
- Apply pressure to puncture site for about 2 minutes to prevent bleeding, then apply sterile dressing
- The aspiration should be performed with care not to injure any important structures in close relationship to the joint and with care to not introduce infection
- Complications associated with synovial fluid aspiration include joint infection and hemorrhage leading to hemarthrosis
Additional information
- 6-12 hours of fasting before test if glucose testing of synovial fluid is required simultaneously
- Do not perform arthrocentesis if there is overlying skin or wound infection
- Label samples and send to lab immediately
Info
- Synovial fluid analysis (cell count/culture) is performed to detect and estimate the cell count, differential, and isolate and identify any microorganisms present in the synovial fluid
- Synovial fluid is found in the cavities of synovial joints lined by synovial membranes and act as a lubricant for the joint and cushions the joint structures
- It is a thick, stringy fluid that is an ultrafiltrate of plasma, and contains hyaluronic acid, lubricin, and glycoproteins
Clinical
- The clinical utility of synovial fluid analysis includes:
- To evaluate the cause and nature of joint effusion
- Aids in the differential diagnosis of arthritis (inflammatory and noninflammatory), particularly septic and crystal-induced arthritis
- To identify septic arthritis
- To differentiate between gout and pseudogout
- Evaluation of undiagnosed articular disease
- Septic arthritis may clinically present with:
- In newborns and infants
- Crying, when the infected joint is moved
- Immobility of the limb of the infected joint
- Irritability
- Fever
- In children and adults
- Intense joint pain
- Joint swelling
- Joint redness
- Unable to move the limb with infected joint
- Fever
- A wide variety of particulate matter can be seen in synovial fluid including cells, fibrin, collagen, cartilage, synovial fragments, rice bodies, bacteria, fungi, crystals, and others
Overview on Gross Appearance, Volume, Viscosity
- Normal and noninflammatory fluid is transparent yellow or straw-colored
- Inflammatory fluid is usually translucent or opaque and more strongly colored
- Fluid that is immediately and uniformly bloody is suggestive of hemarthrosis, whereas blood that appears after aspiration is underway is more likely due to traumatic aspiration
- The viscosity of non-inflammatory conditions is usually normal to slightly high, where as low viscosity is usually seen in inflammatory conditions. The low viscosity is due to reduced production of hyaluronan as well as a reduction in its polymerization, with the resulting hyaluronan being of low molecular weight
Overview on Cell count and differential
- Total WBC count and differential in disease conditions:
| Disease/Condition | WBC count
(per µL) | PMNs |
|---|
| Normal | <200 | <25% |
| Fungal-Viral Arthritis | 2,000-50,000 | - |
| Gout (Acute) | 2,000-75,000 | <90% |
| Lyme Arthritis | 10,000-100,000 | >50% |
| Osteoarthritis | 200-2,000 | - |
| Traumatic | <5,000 (with RBCs) | ~50% |
| Toxic synovitis | 5,000-15,000 | <25% |
| Reiter's Syndrome | 2,000-50,000 | >50% |
Rheumatic fever
(Acute) | 10,000-15,000 | >50% |
| Rheumatoid arthritis | 15,000-80,000 | >50% |
| Septic arthritis | 50,000-200,000 | >90% |
- Low WBC count (<2000/mm3) is seen in some patients with systemic inflammatory conditions such as systemic lupus erythematosus or scleroderma
- Septic joints may have WBC counts <30,000/mm3, especially with gonococcal or tuberculosis infection, or with partially treated bacterial infection
- Immunocompromised patients may not show a typical response to bacterial infection
- Phagocytic inclusions in polymorphonuclear cells suggest rheumatoid arthritis (RA cells)
- Phagocytosis of leukocytes by macrophages is seen in Reiter's syndrome
Overview on Gram stain and Culture
- Common causes of infectious (septic) arthritis include:
- Nongonococcal causes of bacterial arthritis
- Staphylococcus aureus
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Enterobacteriaceae
- Pseudomonas
- Hemophilus influenza
- Neisseria meningitides
- Mycobacterium tuberculosis
- Gonococcal infection (especially young adults)
- Viral infections
- Fungal infections
- The incidence of Hemophilus influenza infection has decreased dramatically since initiation of routine vaccination against this organism
Additional information
- Infectious arthritis most commonly effects the knee followed by shoulder, hip, elbow, and wrist joints
- Factors interfering with test results include:
- Dietary restrictions not followed (especially for glucose)
- Traumatic tap (false increase in RBC count)
- Specimen contamination
- Clotted specimen
- Acid diluents added to specimen for WBC count (alteration in cell count)
- Failure to mix specimen and anticoagulant adequately
- Refrigeration of the sample (increase in monosodium urate crystals secondary to decreased solubility of uric acid)
- Exposure of the sample to room air with a resultant loss of carbon dioxide and rise in pH encourages the formation of calcium pyrophosphate crystals
- Delay in sending sample (gonococci are particularly labile)
- Related laboratory tests include:
Synovial fluid profiles in various disease states:
| Noninflammatory
Class I | Inflammatory
Class II | Purulent
Class III | Hemorrhagic
Class IV |
|---|
| Viscosity | High | Low | Low | Variable |
Appearance
(Clarity, color) | Clear, transparent, or light yellow | Translucent to opaque, dark yellow | Cloudy to opaque, dark yellow to green | Cloudy, pink to red |
| WBC (per µL or per mm3) | 200-2000 | 3000-100,000 | Usually >50,000; often >100,000 | Usually >2000 |
| PMNs* | <25% | 50-90% | >95% | 30% |
| Gram Stain & Culture | Negative | Negative | Often positive | Negative |
| Glucose (mg/dL) | Equal to serum levels | >25 mg/dL (but lower than serum levels) | <25 mg/dL (much lower than serum levels) | Equal to serum levels |
| Protein (g/dL) | 2.0-3.5 | >3 | >3 | >3 |
| Comments | Cartilage cells often present. A bedside test for viscosity shows positive string test when the fluid is dripped from a syringe; a string of >10-15 cm is formed. | Possible presence of rice bodies in acute bacterial arthritis, RA, and tuberculous arthritis. A bedside test for viscosity shows that the synovial fluid drips like water, dripping in small drops from a syringe. | Culture and gram stain positive in only 25% cases of gonorrhea. WBC count and % PMN lower with infections caused by organisms of low virulence or if antibiotic therapy already started. | Many RBCs found. Fat globules strongly suggest intra-articular fracture. |
Full differential diagnosis of each of the 4 classes is present in the "High Result" section of this content.
*PMNs = Polymorphonuclear cells
This section covers Synovial fluid - Cells/Culture. Other section provides detailed information on other components of Synovial fluid analysis.
Nl Result
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
White blood cells
- WBC's <200/mm3
- Differential
- Polymorphonuclear (PMN) cells: <25%
- Lymphocytes: <75%
- Monocytes: <70%
Organisms
- Gram stain: negative
- Acid fast stain: negative
- Culture (Bacterial, Fungal, AFB): negative
This section covers Synovial fluid - Cells/Culture. Other section provides detailed information on other components of Synovial fluid analysis.
High Result
Conditions associated with abnormal findings in synovial fluid (see Clinical Section for table that defines each Class I-IV):
Increased WBC's or PMN's
Conditions associated with 200-2000 WBC/mm3 in the synovial fluid includes:
- Chronic gout
- Chronic pseudogout
- Erythema nodosum
- Fungal/Viral arthritis
- Hypertrophic osteoarthropathy
- Neuropathis arthropathy
- Osteoarthritis
- Osteochondritis dissecans
- Pigmented villonodular synovitis
- Polymyositis
- Progressive systemic sclerosis
- SLE
- Trauma
Conditions associated with 2000-50,000 WBC/mm3 in the synovial fluid includes:
- Acute gout
- Acute pseudogout
- Ankylosing spondylitis
- Bacterial infections (partially treated)
- Fungal/Viral arthritis
- Psoriatic arthritis
- Reiter's disease
- Rheumatic fever
- Rheumatoid arthritis
- Scleroderma
- Septic arthritis
- SLE
Conditions associated with >50,000 WBC/mm3 in the synovial fluid include:
- Septic arthritis
- Acute Gout (rarely)
- Lyme Arthritis (rarely)
- Rheumatoid Arthritis (rarely)
Condition associated with increased polymorphonuclear cells (>50%) in the synovial fluid include:
- Ankylosing spondylitis
- Arthritis accompanying ulcerative colitis and Crohn disease
- Bacterial infection
- Gout (acute)
- Lyme arthritis
- Mycotic infections
- Pseudogout (acute)
- Psoriatic arthritis
- Reiter disease
- Rheumatic fever
- Rheumatoid arthritis
- Sarcoidosis
- Scleroderma
- Septic arthritis
- Systemic lupus erythematosus (SLE)
- Tuberculous infections
- Viral infections
Abnormal findings on Gram Stain or Culture include:
Organisms associated with infectious arthritis include:
- Bacterial
- Gram positive cocci such as Staphylococcus aureus and group A Streptococci (predominant etiologic agents)
- Staphylococcus epidermidis and S aureus (in recently implanted prosthetic implants)
- Pseudomonas aeruginosa and methicillin-resistant S aureus (especially in intravenous drug abusers)
- Salmonella species (common in SLE, Sickle cell disease)
- Pasteurella multocida (usually after a cat bite)
- Mycobacterium tuberculosis and Mycobacterium kansasii (usually from a pulmonary focus)
- Gonococcal (N Gonorrhoea)
- Fungal
- Candida albicans and Candida parapsilosis (especially in debilitated hospitalized patients or on long-term antibacterial therapy)
- Sporothrix schenckii (exposure to moist soil, thorns, or the outdoors)
- Viral
- Parvovirus B 19
- Hepatitis A, B, and C virus
- Rubella virus
- Alphaviruses (West Nile virus, Chikungunya)
- Retroviruses (HIV, HTLV-1)
Classes I-IV of Fluid
- Noninflammatory (Class I)
- Avascular necrosis
- Hypertrophic osteoarthropathy
- Neuropathic arthropathy
- Osteoarthritis or degenerative joint disease
- Osteochondritis dissecans
- Osteochondromatosis
- Pigmented villonodular synovitis
- Subsiding or early inflammation
- Traumatic arthritis
- Inflammatory (Class II)
- Ankylosing spondylitis
- Arthritis accompanying ulcerative colitis and Crohn disease
- Bacterial infection
- Gout (acute)
- Mycotic infections
- Pseudogout (acute)
- Psoriatic arthritis
- Reiter disease
- Rheumatic fever
- Rheumatoid arthritis
- Sarcoidosis
- Scleroderma
- Systemic lupus erythematosus (SLE)
- Tuberculous infections
- Viral infections
- Purulent (Class III)
- Pyogenic bacterial infection (eg, N gonorrhoeae, S aureus), gonococci
- Tuberculosis
- Septic arthritis
- Hemorrhagic (Class IV)
- Hemangioma
- Hemophilia or other hemorrhagic diathesis
- Neuropathic arthropathy
- Pigmented villonodular synovitis
- Synovioma
- Trauma with or without fracture
This section covers Synovial fluid - Cells/Culture. Other section provides detailed information on other components of Synovial fluid analysis.
References
- ARUP Laboratories®. Body Fluid Culture (Includes Gram Stain 0060101). [Homepage on the internet]©2007. Last accessed on September 11, 2007. Available at URL: http://www.aruplab.com/guides/ug/tests/0060108.htm
- ARUP Laboratories®. Cell Count, Body Fluid. [Homepage on the internet]©2007. Last accessed on September 11, 2007. Available at URL: http://www.aruplab.com/guides/ug/tests/0095019.htm
- Brannan SR et al. Synovial fluid analysis. J Emerg Med. 2006 Apr;30(3):331-9.
- Chong YY et al. The value of joint aspirations in the diagnosis and management of arthritis in a hospital-based rheumatology service. Ann Acad Med Singapore. 2007 Feb;36(2):106-9.
- eMedicine from WebMD®. Gout and Pseudogout. [Homepage on the Internet] ©1996-2007. Last updated on March 14, 2007. Last accessed on September 11, 2007. Available at URL: http://www.emedicine.com/emerg/topic221.htm
- eMedicine from WebMD®. Nongonococcal Infectious Arthritis. [Homepage on the Internet] ©1996-2007. Last updated on June 21, 2005. Last accessed on September 11, 2007. Available at URL: http://www.emedicine.com/med/topic2935.htm
- Laboratory Corporation of America®. Cell Count, Synovial Fluid. [Homepage on the internet]©2007. Last accessed on September 11, 2007. Available at URL: http://www.labcorp.com/datasets/labcorp/html/chapter/mono/he005800.htm
- Li SF et al. Diagnostic utility of laboratory tests in septic arthritis. Emerg Med J. 2007 Feb;24(2):75-7.