Synovial Fluid Analysis

What is synovial fluid?

Viscous fluid

Where is synovial fluid found?

Within synovial joints

How is synovial fluid formed?

• Ultrafiltration of plasma across the synovial membrane

• Secretions from synoviocytes

What is the main function of synovial fluid?

• Lubrication

• Nutrient delivery to articular cartilage

• Absorbent material during joint compression

What are synoviocytes?

Specialized cells found in the synovial membrane that lines the joint space

What are the two types of synoviocytes?

• Type A

• Type B

Which synoviocyte type is more predominant?

Type A

What is the main function of Type A synoviocytes regarding cellular clean up?

They are actively phagocytic and remove waste and cell debris

What enzymes do Type A synoviocytes synthesizes?

Degradative enzymes such as collagenases

What substances do Type B synoviocytes synthesize?

Hyaluronate, a mucopolysaccharide

What effect do Type B synoviocytes have on synovial fluid?

They make the fluid viscous

Are both types of synoviocytes necessary for the joint?

Yes

What are the four main classifications pf joint disorders (arthritis)

• Non-inflammatory

• Inflammatory

• Septic

• Hemorrhagic

What characterizes noninflammatory joint disorders?

They are joint disorders without significant inflammation

What is a primary example of a noninflammatory joint disorder?

Osteoarthritis (degenerative conditions)

What characterizes inflammatory joint disorders?

They are joint disorder with inflammation in the joint

How does the viscosity of synovial fluid change in inflammatory joint disorders?

It has low viscosity

What are some immunologic and systemic conditions classified as inflammatory joint disorders?

• Systemic lupus erythematosus

• Rheumatoid arthritis

• Lyme disease

• Gout

• Pseudo-gout

What causes septic joint disorders?

Microbial infections

What characteriszes hemorrhagic joint disorders?

Joint disorders involving bleeding into the joint

What are the three common causes of hemorrhagic joint disorders?

• Trauma

• Tumors

• Coagulation deficiencies

What is arthrocentesis?

The aspiration of synovial fluid from a joint space for diagnostic testing

What fast is recommended for a patient before arthrocentesis?

The patient should fast for 4-6 hours (not always necessary)

When should a blood sample be collected relative to arthrocentesis?

A blood sample should be collected at the same time.

What is the normal volume of synovial fluid in a joint

0.1-3.5 mL

How much synovial fluid can an inflamed joint contain?

More than 25 mL

What does the term “dry tap” mean in arthrocentesis?

It occurs when arthrocentesis is performed on a joint without fluid buildup.

What additive is used in Tube #1, and what is its purpose?

It has no additive and is used for chemical testing (such as glucose, protein, and uric acid)

What additive is in Tube #2, and what color top does it have?

Anticoagulant (EDTA), which has a purple top

What testing is performed using Tube #2?

• Microscopic studies

• Cell counts

• Crystals

What container/top is used for Tube #3, and what testing is it used for?

A sterile container (green top) used for Gram stain, culture, and sensitivity testing

What are the storage and handling conditions for synovial fluid samples?

Transport at room temperature and analyze as soon as possible after collection

What is the normal color and clarity of synovial fluid?

Pale yellow or colorless, and clear

What does a red or brown synovial fluid color indicate?

Traumatic collection or blood entering the joint cavity

What does a greenish or purulent color indicate?

Infection

What conditions are associated with a milky color?

• Tuberculous arthritis

• Systemic lupus erythematosus (SLE)

What cellular elements can cause synovial fluid to look cloudy?

• WBCs

• RBCs

• Synoviocytes

What non-cellular components can make synovial fluid cloudy?

• Crystals

• Fat droplets

• Fibrin

• Cellular debris

• Rice bodies

What are rice bodies?

White, free-floating substances made of collagen, covered by fibrinous tissue that resemble polished, shiny grains of rice

What disease is most commonly associated with rice bodies?

Rheumatoid arthritis

What is the normal viscosity of synovial fluid, and what causes it?

It is normally high due to a high concentration of mucoprotein hyaluronate.

What causes decreased viscosity in synovial fluid?

Hyaluronate can be broken down (depolymerized) by hyaluronidase from bacteria and neutrophils, or other diseases can inhibit hyaluronate production by synoviocytes

What is a normal result for the string test?

It forms a string that is at least 4 cm long when expelled from a collection syringe

Does normal synovial fluid form clots?

No

What does a spontaneous clot in synovial fluid indicate?

It indicates the abnormal presence of fibrinogen

Why might fibrinogen be present in synvoial fluid?

Due to pathologic processes that damage the synvoial membrane or traumatic arthrocentesis involving blood contamination

What instrument is used to count cells in synovial fluid analysis?

A hemocytometer

What is normally used as a diluent if necessary, depending on the cell count?

Normal saline

Why is acetic acid not used as a diluent for synovial fluid cell counts?

Because it is not acetic acid

Why might an extended settling time be needed when counting cells in the hemocytometer?

If the sample is very viscous

What buffer may be used as a diluent to reduce viscosity for more efficient cell counting?

Hyaluronidase buffer

What is the normal reference range for RBCs in synovial fluid?

Less than 2,000 per microliter

When are RBC counts increased in synovial fluid?

In traumatic taps or hemorrhagic effusions

What is the normal reference range for WBCs in synovial fluid?

Less than 200 per microliter

When are WBC counts increased in synovial fluid?

In bacterial arthritis, though other conditions can also cause an increase

Are total WBC counts of high or limited value in identifying a specific disease process?

Limited value

What is the normal percentage of monocytes or macrophages in a WBC differential count?

60%

What is the normal percentage of lymphocytes in a WBC differential cell count?

30%

What is the normal percentage of neutrophils in a WBC differential cell count?

10%

What prepartion cell count of limited diagnostic value?

Because cells can differ not only with the disease process but also with the stage of the disease

What conditions is indicated if more than 80% neutrophils are present?

Bacterial arthritis and urate gout

How should samples be maintained and examined for crystal identification?

Maintain the sample at room temperature and perform the examination immediatley

What preparations can be used for crystal examination?

• Wet preparations

• Cytospin slides

What type of microscopy should be used to identify crystals?

Polarized microscopy

What is the full name and compostion of MSU crystals?

Monosodium urate

What shape are MSU crystals?

Needle-shaped

What is the birefringence of MSU crystals under polarized light?

Gouty arthritis

What factors contribute to MSU crystal formation?

• Impaired purine metabolism

• High purine foods

• Decreased renal excretion of uric acid

What is the full name and composition of CPPD crystals?

Calcium pyrophosphate dihydrate

What shape are CPPD crystals?

Rhomboid or rectangular

What is birefringence of CPPD crystals under polarized light?

Weakly positive (blue when parallel, yellow when perpendicular)

What conditions is associated with CPPD crystals?

Pseudogout

What other conditions are associated with CPPD crystal formation?

• Degenerative arthritis

• Arthritis accompanying metabolic diseases

• Disorders causing elevated calcium levels

What is the apperance of Cholesterol crystals?

Notched, rhombic plates (extracellular)

What is the birefringence of Cholesterol crystals?

Negative birefringence

What conditions and preparations are associated with Cholesterol crystals

Seen in wet preparations or unstained cytospin slides

• Chronic inflammation

• SLE

• RA

What is the appearance of Corticosteroid crystals?

Flat, variable-shaped plates

What is the birefringence of Corticosteroid crystals?

Both positive and negative birefringence

What conditions/cause is associated with Corticosteroid crystals?

Injections; they may remain visible for months after an injection

What shape/appearance do Calcium oxalate crystals have?

Envelopes

What is the birefringence of Calcium oxalate crystals?

Negative birefringence

What patient population is associated with Calcium oxalate crystals?

Renal dialysis patients

What is the appearance of Apatite (Calcium phosphate) crystals?

Small particles; they require electron microscopy to be seen

What is the birefringence of Apatite (Calcium phosphate) crystals?

No birefringence

What conditions is associated with Apatite (Calcium phosphate) crystals?

Osteoarthritis

What is the normal glucose level in synovial fluid relative to plasma?

It is within 10 mg/dL of plasma

How does synvoial fluid glucose change in inflammatory and septic conditions

It is decreased

What is the difference between plasma and synovial fluid glucose in septic conditions?

The difference may exceed 40 mg/dL

When should a plasma sample be drawn relative to synovial fluid glucose in septic conditons

The difference may exceed 40 mg/dL

When should a plasma sample be drawn relative to synovial fluid for glucose testing?

At the same time

What is the normal level of total protein in synvoial fluid?

Less than 3 g/dL

How does normal synovial fluid protein compare to plasma?

It is typically ¼ to ½ of plasma

When is total protein increased in synvoail fluid?

In inflammatory and hemorrhagic disorders

What does increased total protein indicate?

An inflammatory process

What is the normal level of uric acid in synvoail fluid?

The same levels as plasma

What can abnormal, increased levels of uric acid in synvoail fluid cause?

MSU crystals

Is there an established reference value for lactate in synovial fluid?

No established reference value

When is lactate increased in synovial fluid?

When there is anaerboic glycolysis in the synovium

What conditions are associated with increased lactate in synovial fluid

Severe inflammatory processes