Synovial Fluid Analysis

What is synovial fluid?

A viscous fluid

Where is synovial fluid found?

Within synovial joints

How is synovial fluid formed?

By ultrafiltration of plasma across the synovial membrane

What cells also contribute secretions to synovial fluid?

Synoviocytes

What are the main functions of synovial fluid?

Lubrication; nutrient delivery to articular cartilage; absorption of force during joint compression

What are synoviocytes?

Specialized cells in the synovial membrane lining the joint space

What are the two types of synoviocytes?

Type A and Type B

Which type of synoviocyte is more predominant?

Type A

What is the main function of Type A synoviocytes?

Phagocytosis; they remove waste and cell debris

What enzymes do Type A synoviocytes produce?

Degradative enzymes

What substance do Type B synoviocytes produce?

Hyaluronate

What effect does hyaluronate have on synovial fluid?

It makes the fluid viscous

Are both types of synoviocytes necessary for the joint?

Yes

What are the four main classifications of joint disorders (arthritis)?

Noninflammatory; inflammatory; septic; hemorrhagic

What characterizes noninflammatory joint disorders?

Joint disorders without significant inflammation

What is a common example of a noninflammatory joint disorder?

Osteoarthritis (a degenerative condition)

What characterizes inflammatory joint disorders?

Joint disorders involving inflammation

How does synovial fluid viscosity change in inflammatory joint disorders?

It decreases

Which conditions are classified as inflammatory joint disorders?

Systemic lupus erythematosus (SLE); rheumatoid arthritis; Lyme disease; gout; pseudogout

What causes septic joint disorders?

Microbial infections

What characterizes hemorrhagic joint disorders?

Bleeding into the joint

What are three common causes of hemorrhagic joint disorders?

Trauma; tumors; coagulation deficiencies

What is arthrocentesis?

Aspiration of synovial fluid from a joint for diagnostic testing

How long should a patient fast before arthrocentesis?

4–6 hours may be recommended

When should a blood sample be collected in relation to arthrocentesis?

At the same time as the synovial fluid sample

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 a dry tap mean during arthrocentesis?

No fluid is obtained because there is no fluid buildup in the joint

What is collected in Tube #1

and what is it used for?

What additive is used in Tube #2?

EDTA anticoagulant

What color top is associated with Tube #2?

Purple

What tests are performed on Tube #2?

Microscopic studies

What is Tube #3 used for?

Microbiology testing

What type of container is used for Tube #3?

A sterile container; confirm the tube-top color with your course materials

How should synovial fluid samples be transported and handled?

Transport at room temperature and analyze as soon as possible

What is the normal color and clarity of synovial fluid?

Pale yellow or colorless and clear

What can red or brown synovial fluid indicate?

Traumatic collection or blood entering the joint cavity

What can greenish or purulent synovial fluid indicate?

Infection

What conditions may be associated with milky synovial fluid?

Tuberculous arthritis and systemic lupus erythematosus (SLE)

Which cellular elements can make synovial fluid appear cloudy?

White blood cells (WBCs); red blood cells (RBCs); synoviocytes

Which noncellular components can make synovial fluid appear cloudy?

Crystals; fat droplets; fibrin; cellular debris; rice bodies

What are rice bodies?

White

What disease is most commonly associated with rice bodies?

Rheumatoid arthritis

Why is normal synovial fluid highly viscous?

Because it contains a high concentration of hyaluronate

What can cause decreased synovial fluid viscosity?

Hyaluronate breakdown by hyaluronidase from bacteria or neutrophils

What is a normal result for the synovial fluid string test?

A string at least 4 cm long forms when fluid is expelled from a collection syringe

Does normal synovial fluid form clots?

No

What does spontaneous clotting of synovial fluid indicate?

Abnormal presence of fibrinogen

Why might fibrinogen be present in synovial fluid?

Damage to the synovial membrane or blood contamination from traumatic arthrocentesis

What instrument is used to count cells in synovial fluid?

A hemocytometer

What diluent may be used for synovial fluid cell counts

depending on the cell count?

Why should the acetic acid diluent card be checked against the lecture notes?

The supplied answer was incorrect and did not explain why acetic acid is avoided

When might an extended settling time be needed during hemocytometer cell counting?

When the sample is very viscous

What buffer may be used to reduce synovial fluid viscosity for cell counting?

Hyaluronidase buffer

What is the normal RBC reference range in synovial fluid?

Less than 2

When are synovial fluid RBC counts increased?

In traumatic taps or hemorrhagic effusions

What is the normal WBC reference range in synovial fluid?

Less than 200/µL

When are synovial fluid WBC counts increased?

In bacterial arthritis and other joint conditions

Are total synovial fluid WBC counts highly specific for identifying a disease?

No; they have limited diagnostic value

What is the normal percentage of monocytes or macrophages in the synovial fluid differential?

60%

What is the normal percentage of lymphocytes in the synovial fluid differential?

30%

What is the normal percentage of neutrophils in the synovial fluid differential?

10%

Why is the synovial fluid differential cell count of limited diagnostic value?

Cell types can vary with both the disease process and the stage of disease

What conditions may be indicated by more than 80% neutrophils?

Bacterial arthritis and urate gout

How should synovial fluid be handled for crystal identification?

Keep it at room temperature and examine it immediately

What preparations can be used for synovial fluid crystal examination?

Wet preparations and cytospin slides

What type of microscopy is used to identify synovial fluid crystals?

Polarized microscopy

What does MSU stand for?

Monosodium urate

What shape are MSU crystals?

Needle-shaped

What is the birefringence of MSU crystals?

Strongly negative birefringence

What colors do MSU crystals show with a compensator?

Yellow when parallel and blue when perpendicular to the compensator axis

What condition is associated with MSU crystals?

Gouty arthritis

What factors contribute to MSU crystal formation?

Impaired purine metabolism; high-purine foods; decreased renal excretion of uric acid

What does CPPD stand for?

Calcium pyrophosphate dihydrate

What shape are CPPD crystals?

Rhomboid or rectangular

What is the birefringence of CPPD crystals?

Weakly positive birefringence

What colors do CPPD crystals show with a compensator?

Blue when parallel and yellow when perpendicular to the compensator axis

What condition is associated with CPPD crystals?

Pseudogout

What other conditions are associated with CPPD crystal formation?

Degenerative arthritis; arthritis associated with metabolic diseases; disorders causing elevated calcium levels

What is the appearance of cholesterol crystals?

Notched

What is the birefringence of cholesterol crystals?

Negative birefringence

How may cholesterol crystals be observed?

In wet preparations or unstained cytospin slides

What conditions are associated with cholesterol crystals?

Chronic inflammation; SLE; rheumatoid arthritis

What is the appearance of corticosteroid crystals?

Flat plates with variable shapes

What is the birefringence of corticosteroid crystals?

Both positive and negative birefringence

Why might corticosteroid crystals be found in synovial fluid?

After injections; they may remain visible for months

What is the appearance of calcium oxalate crystals?

Envelope-shaped

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 that require electron microscopy to be seen

What is the birefringence of apatite crystals?

No birefringence

What condition is associated with apatite crystals?

Osteoarthritis

How does normal synovial fluid glucose compare with plasma glucose?

It is within 10 mg/dL of the plasma glucose level

How does synovial fluid glucose change in inflammatory and septic conditions?

It decreases

How large can the difference between plasma and synovial fluid glucose be in septic conditions?

It may exceed 40 mg/dL

When should plasma be collected for comparison with synovial fluid glucose?

At the same time as the synovial fluid sample

What is the normal total protein level in synovial fluid?

Less than 3 g/dL

How does normal synovial fluid protein compare with plasma protein?

It is typically one-quarter to one-half of the plasma level

When is total protein increased in synovial fluid?

In inflammatory and hemorrhagic disorders

What can increased synovial fluid total protein indicate?

An inflammatory process