Synovial Fluid

Synovial Fluid

• formed by ultrafiltration of plasma

  • synovial membrane

  • secretion by synoviocytes

Synovial Fluid functions

• viscous fluid to lubricate joints

• nutrient source for articular cartilage

• absorbent material for joint compression 

Type A Synovial Fluid

• more predominant 

• actively phagocytic 

• synthesizes degradative enzymes (Collagenases)

• removes waste and debris

Type B synovial fluid

• synthesizes hyaluronate, a mucopolysaccharide

• makes fluid viscous 

What are the 4 joint disorder classifications

• Noninflammatory

• Inflammatory

• Septic

• Hemorrhagic

Noninflammatory Joint Disorder

• degenerative, osteoarthritis

Inflammatory Joint Disorder

• immunologic, SLE, rheumatoid arthritis, lyme disease, gout and pseudogout

Septic Joint Disorder

• microbial infection

Hemorrhagic Joint Disorder

• trauma, tumors, coagulation deficiencies 

Normal Synovial Fluid

volume: <3.5 ml

color: pale yellow

viscosity: high 

WBC : <200 

neutrophils: <25%

glucose: approx. equal to plasma

glucose P-SF : <10 mg/dL

culture: negative

Noninflammatory Synovial FLuid

volume: >3.5 ml

color: yellow

viscosity: high 

WBC : <3000 

neutrophils: <25%

glucose: approx. equal to plasma

glucose P-SF : <20 mg/dL

culture: negative

Inflammatory Synovial Fluid

volume: >3.5 ml

color: yellow-white

viscosity: low 

WBC : 2000-100,000

neutrophils: >50%

glucose: less than plasma

glucose P-SF : >20 mg/dL

culture: negative

Septic Synovial Fluid

volume: >3.5 ml

color: yellow-green 

viscosity: low 

WBC : 10,000-100,000

neutrophils: >75% 

glucose: less than plasma

glucose P-SF : >40 mg/dL

culture: positive

Hemorrhagic Synovial Fluid

volume: >3.5 ml

color: red-brown 

viscosity: decreased 

WBC : >5,000

neutrophils: >25%

glucose: approx. equal to plasma

glucose P-SF : <20 mg/dL

culture: negative

Arthrocentesis

• aspiration from a joint 

requirements for arthrocentesis collection

• patient should be fasting a min 4-6 hrs

• blood sample should be collected at same time

• formal volume: -.1-3.5 ml 

• transport and analyze at room temp

a fluid volume of what means an inflamed joint? 

• >25 ml 

dry tap

• arthrocentesis of a joint with no fluid build up 

What are the three collection tubes used for synovial fluid collection 

1. no anticoagulant 

   1. chemical/immunologic

2. anticoagulant 

   1. microscopic, cell counts

3. sterile anticoagulate 

   1. microbiology 

What is used in synovial fluid formation to prevent crystal formation?

• sodium heparin or EDTA

Normal color for synovial fluid

• pale yellow or colorless and clear

what could red/brown synovial fluid mean?

• trauma during collection 

• disorders that disrupt synovial membrane allowing blood to enter joint cavity 

Greenish or purulent synovial fluid could mean…

• infectious

milky synovial fluid could indicate what?

• tuberculous arthritis

• SLE

What could cause synovial fluid to be cloudy

• WBC, RBC, synoviocytes

• crystals, fat droplets

• fibrin, cell debris, rice bodies

Rice bodies

• white, free floating substances made of collagen covered by fibrinous tissue 

where are rice bodies most commonly seen?

• rheumatoid arthritis 

Normal viscosity of synovial fluid

• normally very high due to high concentration of mucoprotein hyaluronate 

What happens to viscosity during inflammatory conditions

• hyaluronate can become depolymerized by enzyme hyaluronidase 

what should normal synovial fluid look like in a collection syringe 

• should show string formation when expelled 

  • at least 4 cm long

what can change the viscosity of synovial fluid

• enzyme hyaluronidase (inflammatory conditions)

• diseases that inhibit production/secretion of hyaluronate by synoviocytes

What can cause a spontaneous clot to form in synovial fluid? 

• abnormal presence of fibrinogen 

T/F normal synovial fluid does not clot

• true 

What would cause fibrinogen to be present in synovial fluid

• pathologic process that damage synovial membrane

• traumatic arthrocentesis with blood contamination 

What is used for microscopic examination of synovial fluid

• hemocytometer 

What is used as a diluent for the hemocytometer?

• saline 

• hyaluronidase buffer can also be used to reduce viscosity for more efficient county 

why would hyaluronidase buffer be used as a diluent for the hemacytometer?

• reduce viscosity for more efficient counting 

what is not used as a buffer when using a hemacytometer for microscopic evaluation of synovial fluid? 

• acetic acid 

What is normal RBC count for synovial fluid

• less than 2000/ul 

What can increased RBC indicate

• traumatic tap 

• hemorrhagic effusions

What is the normal WBC in synovial fluid

• less than 200/ul 

What can increased WBC indicate

• bacterial arthritis 

what are normal centrifugation amounts of WBC

• 60% monocytes/macrophages

• 30% lymphocytes

• 10% neutrophils 

what does it mean if over 80% are neutrophils

• bacterial arthritis

• urate gout 

What can WBC differentiate

• disease process and stage of disease 

How should crystals be identified in synovial fluid?

• maintain sample at room temp/examine immediately 

• use wet preparations or cytospin slides 

what method is used to identify crystals

• polarized microscopy 

What are the two main crystaled identified using polarized microscopy 

• monosodium urate (MSU)

• calcium pyrophosphate dihydrate (CPPD)

Monosodium Urate (MSU) Crystals

• needle-like with pointed ends 

• seen in intra/extra cellularly 

what do MSU crystals look like in polarized microscopy? 

• strongly birefringent 

• bright against a black background

What do MSU crystals look like with a red compensator? 

• appear yellow when longitudinal axes are parallel 

• appear blue when perpendicular 

What conditions have MSU Crystals?

• gouty arthritis

• impaired purine metabolism 

• high purine foods

• leukemia chemotherapy 

• decreased renal excretion of uric acid

Calcium Pyrophosphate Dihydrate (CPPD) Crystals

• smaller/blunter 

• rodlike, rhomboid, or square

what do CPPD crystals look like in polarized microscopy?

• weak positive birefringence with colors opposite MSU

What do CPPD crystals look like with a red compesator

• blue when longitude axis is parallel

• yellow when perpendicular

What conditions have CPPD crystals

• degenerative arthritis

• arthritis accompanying metabolic diseases

• disorders causing elevated calcium levels

• pseudogout 

Cholesterol Crystals 

• observed via wet preparation or unstained cytospin slide

• flat, rectangular plates

what conditions have cholesterol crystals

• chronic inflammation

• systemic autoimmune disease

  • SLE and RA

Other possible crystals

• corticosteroid injections

  • look like glass shards

• calcium oxalate

  • renal dialysis patients

• artifacts

  • starch, powered anticoagulants, dust, scratches

Glucose levels in synovial fluid

• should have same levels as plasma 

  • difference should be less than 10 mg/dl of plasma level 

When should plasma be drawn

• same time as synovial fluid

what conditions can cause a significant decrease glucose in fluid 

• inflammatory (>20 mg/dl)

• septic (>40 mg/dl)

Total protein in synovial fluid

• normally > 3 g/dl

• typically ½ to ¼ that of plasma

what causes increased total protein

• joint diseases 

  • indicates an inflammatory process

Uric acid

• levels should be that same as plasma

what can happen if there are increased levels of uric acid? 

• MSU crystal formation 

what causes lactate to be increased

• anaerobic glycolysis 

• severe inflammatory processes

Normal Synovial Fluid

Vol: <3.5 ml

color: pale yellow/colorless

clarity: clear

viscosity: able to form string 4-6 cm long

leukocyte: <200 cells/ul

neutrophils: <25% of differential

crystals: none

glucose: <10 mg/dl lower than blood glucose plasma

total protein: 3 g/dl

Why is gram stain useful?

• may offer useful diagnostic information when positive

• most infectious agents are bacterial and come from blood 

• 75% of patents with staphylococcal infections identified as positive by gram stain 

• 50% of gram negative organisms

• 40% gonococcal infections 

when should synovial samples be cultured?

• when bacterial or septic arthritis is suspected

artifacts

Calcium Oxalate

corticosteroid injections

cholesterol

• CPPD crystals with red compensator

MSU Crystals with red compensator 

MSU Crystals

MSU Crystals in polarized microscopy