Chapter 11: Synovial Fluid Analysis

Synovial Fluid

• formed by ultrafiltration of plasma across synovial membrane and from secretions by synoviocytes

Synovial Fluid Importance

• viscous fluid- acts as lubricant

• nutrient source for metabolically active cartilage

• absorbent material for joint compression

Type A Synovial Fluid

• more predominant

• actively phagocytic

• synthesizes enzymes

• removes waste and cell debris

Type B Synovial Fluid

• synthesizes hyaluronate 

• makes fluid viscous 

What are the 4 Joint Disorder Classifications

• Noninflammatory

• Inflammatory

• Septic
  hemorrhagic

Non Inflammatory Joint Disorder

• degenerative

• osteoarthritis

Inflammatory Joint Disorder

• immunogenic, SLE, rheumatoid arthritis, lyme disease, gout, pseudogout

• low viscosity

Septic Joint Disorder

• microbial infection

Hemorrhagic

• trauma

• tumors

• coagulation deficiencies 

What are indicators of non inflammatory Joint Disorders

Collor: Yellow

Viscosity: High

WBC Count : <3000

Neutrophils: <25%

glucose: approx equal to plasma level 

Glucose: <20 mg/dL

Culture: Negative 

What are indicators of inflammatory Joint Disorders

Color: Yellow-White

Viscosity: Low

WBC count: 2000-100,000

Neutrophils: >50%

glucose: less than plasma level

Glucose: >20 mg/dL

Culture: negative

What are indicators of septic Joint Disorders

Color: yellow-green

Viscosity: Low 

WBC Count: 10,000-100,000

Neutrophils: >75%

Glucose: less than plasma level

Glucose: >40 mg/dL

Culture: Positive

What are indicators of Hemorrhagic Joint Disorders

Color: red-brown 

Viscosity: decreased

WBC Cells: >5000

Neutrophils: >25%

Glucose: approx = to plasma level 

glucose: <20 mg/dL

culture: negative

Arthrocentesis

• collection via aspiration from a joint 

• patient should be fasting a min 4-6 hours 

• blood sample collected at same time

Dry Tap

• arthrocentesis of a joint with no fluid buildup

Normal fluid volume : sinovial fluid

0.1 to 3.5 ml

• > 25 ml for inflamed joints

Tube #1

• no anticoagulant

  • chemical and immunologic studies

Tube #2

• Anticoagulant 

  • microscopic studies, cell counts, crystals

Tube #3

• sterile anticoagulant 

  • microbiology 

Collection and handling of synovial fluid

• collected in 3 tubes

• sodium heparin or EDTA is used to prevent crystal formation

• transport an analyze at room temp 

What is the normal synovial fluid color?

• pale yellow or colorless and clear

What can red-brown synovial fluid color indicate? 

• trauma during collection 

• disorders allowing blood to enter joint cavity 

What can greenish or purulent synovial fluid color indicate? 

• infections 

What can milky synovial fluid indicate? 

• tuberculous arthritis

• systemic lupus erythematosus (SLE)

Cloudy synovial fluid means what?

• presence of:

  • WBC, RBC, synoviocytes

  • crystals, fat droplets

  • fibrin, cellular debris, rice bodies

Rice Bodies

• white, free floating substances

• made of collagen covered by fibrinous tissue

What condition would you see rice bodies in?

• rheumatoid arthritis

What is the normal viscosity of synovial fluid?

• very high due to high concentration of mucoprotein and hyaluronate 

what causes hyaluronate to be depolarized by enzyme hyaluronidase?

• inflammatory conditions 

What does normal synovial fluid viscosity look like?

• string formation of fluid when expelled from a collection syringe 

How do spontaneous clots form in synovial fluid?

• abnormal presence of fibrinogen 

  • normally synovial fluid does NOT clot 

What does it mean when fibrinogen is present in synovial fluid? 

• pathologic processes that damage synovial membrane

  • traumatic arthrocentesis with blood contamination

What device is used to microscopically examine synovial fluid

• hemocytometer to conduct cell counts

• saline is used as a dilutent 

• hyaluronidase buffer can also be used as a diluent 

What is never used as a buffer in microscopic evaluation of synovial fluid? 

• acetic acid 

What is the normal RBC count in synovial fluid

• less than 2000/uL

What can increased RBC indicate in synovial fluid?

• trauma tap 

• hemorrhagic effusion 

What is the normal WBC in synovial fluid?

• less than 200/uL

what do limited WBC indicate? 

• specific disease process

What do increased WBC indicate?

• bacterial arthritis

Cytocentrifugation results

• 60%: monocytes/macrophages

• 30% lymphocytes

• 10% neutrophils 

what does more than 80% neutrophils in synovial fluid indicate?

• bacterial arthritis and urate gout 

What technique can be used to ID crystals?

• polarized microscopy 

  • monosodium urate

  • calcium pyrophosphate dihydrate 

What are important factors of crystal ID?

• maintain sample at room temperature

• use wet preparations or cytospin slides 

Monosodium Urate Crystals

• needle-like with pointed ends

• seen intra and extra cellularly 

• polarized microscopy 

  • strongly birefringent 

    • bright against black bactrogound

Where are Monosodium Urate Crystals seen?

• gouty arthritis

• impaired purine metabolism 

• high purine foods

• leukemia chemotherapy 

• decreased renal excretion of uric acid

Calcium Pyrophosphate Dihydrate Crystals

• smaller, blunter than MSU crystals 

  • rodlike, rhomboid, or square in shape 

• seen with polarized microscopy 

  • display week positive birefringence with colors opposite of MSU

What does MSU look like with a red compensator

• appear yellow when longitudinal axes are parallel

• blue when perpendicular

What do CPPD crystals look like with compensator

• blue when longitudinal axis

• yellow when perpendicular

Where are CPPD crystals seen?

• degenerative arthritis

• arthritis accompanying metabolic diseases

• disorders causing elevated Ca levels

• Pseudogout

Cholesterol Crystals 

• observe on wet preparation or unstained cytospin slide

• flat, regular plates with corners

• seen in chronic inflammation and systemic autoimmune diseases

What other crystals are ID in synovial fluid

• corticosteroid injections 

  • appear as shards of glass

• calcium oxalate

  • renal dialysis patients

• artifacts

  • starch, powdered anticoagulants, dust

Synovial Fluid Reference Values

Volume: < 3.5 ml

Color: pale-yellow

Clarity: clear

Viscosity: able to form a string of 4-6 cm long

Leukocyte count: <200 cells/ul

neutropjils: <25% of differential

crystals: none

glucose: <10 mg/dL

total protein: 3 g/dL

Glucose levels in synovial fluid

• same levels as plasma (<10 mg/dL)

• plasma should be drawn at same time as synovial fluid

• some diseases decrease glucose in fluid by ½ of what is present in plasma

Abnormal glucose values

• inflammatory : >20 mg/dl

• septic: >40 mg/dl

Total Protein in synovial fluid

• normally less than 3 g/dl

  • typically ½ to ¼ that of plasma 

what does an increase in protein indicate

• caused by joint diseases

• indicates inflamatory process

Uric Acid

• same levels as plasma 

• increased levels may cause MSU crystals

Lactate

• increased from anerobic glycolysis in synovium

• severe inflammatory process

• clinical value not yet established

Gram Stain and Culture

• offer immediately useful diagnostic information when positive

• most infectious agents are bacterial and come from blood

• all synovial fluid samples should be cultured when bacterial or septic arthritis are suspected