Body Fluids- Synovial Fluids

Synovial fluid

Viscous ultrafiltrate of plasma found in movable joint cavities

Primary function of synovial fluid

Lubricates joints and absorbs shock during movement

Main constituent of synovial fluid

Hyaluronic acid produced by synovial lining cells

Origin of synovial fluid

Ultrafiltrate of plasma with added hyaluronic acid and proteins

Arthrocentesis

Needle aspiration of synovial fluid from a joint space

Indications for synovial fluid analysis

Arthritis, infection, trauma, metabolic disorders, crystal disease

Normal synovial fluid volume

Less than 3

5 milliliters

Normal synovial fluid color

Pale yellow

Normal synovial fluid clarity

Clear

Normal synovial fluid viscosity

Forms a 4 to 6 centimeter string

Normal synovial WBC count

Less than 200 cells per microliter

Normal synovial RBC count

Very few to none present

Normal synovial differential

Monocytes and macrophages predominate

Abnormal synovial fluid color

Cloudy, milky, red, or yellow green

Turbid synovial fluid

Indicates increased WBCs, fibrin, or debris

Milky synovial fluid

Suggests crystal-induced inflammation or high lipid content

Bloody synovial fluid

Seen in trauma or hemorrhagic disorders

Specimen handling synovial fluid

Analyze immediately to prevent cell degeneration

Effect of delayed analysis

Causes falsely low cell counts and altered differentials

Anticoagulant for synovial cell counts

EDTA tube

Anticoagulant for synovial cultures

Sodium heparin tube

Diluent for synovial WBC counts

Normal saline, not WBC diluting fluid

Use of hyaluronidase

Reduces viscosity for accurate cell counts

String test

Assesses synovial fluid viscosity by string length

Decreased string length

Seen in inflammatory arthritis

Mucin clot test

Assesses hyaluronic acid polymerization using acetic acid

Normal mucin clot

Forms a firm clot with clear surrounding fluid

Poor mucin clot

Indicates inflammatory arthritis with degraded hyaluronate

Clinical use of mucin clot test

Confirmatory only, not routinely performed

Synovial WBC count most diagnostic test

White blood cell count

Low synovial WBC count

Seen in non-inflammatory joint disorders

Moderate synovial WBC count

wbc- Seen in inflammatory arthritis

Very high synovial WBC count

Suggests septic arthritis

Neutrophils in synovial fluid

Indicate infection or crystal-induced inflammation

Neutrophils greater than 90 percent

Strongly suggest septic arthritis

Lymphocytes in synovial fluid

Seen in chronic non-septic inflammation

Monocytes and macrophages

Predominate in normal synovial fluid

Reiter cells

Macrophages containing ingested neutrophils indicating inflammation

Ragocytes

Neutrophils with immune complex granules seen in rheumatoid arthritis

Lipid droplets in synovial fluid

Associated with traumatic injury

Hemorrhagic synovial fluid

Seen in trauma or coagulation disorders

Traumatic synovial fluid

Blood introduced from joint injury

Hemorrhagic versus traumatic distinction

Hemorrhagic fluid shows persistent blood without injury history

Synovial RBC count significance

Supports trauma or bleeding but not diagnostic alone

Crystal identification

Most important diagnostic test in acute arthritis

Timing of crystal analysis

Must be performed immediately after collection

Crystal reporting rule

Must report intracellular or extracellular location

Effect of refrigeration on crystals

Can alter crystal appearance and birefringence

Monosodium urate crystals

Needle-shaped crystals seen in gout

Location of MSU crystals

Often intracellular within neutrophils

MSU birefringence

Negative birefringence appearing yellow when parallel

Cause of gout

Impaired purine metabolism with decreased uric acid excretion

Calcium pyrophosphate crystals

Rhomboid-shaped crystals seen in pseudogout

Location of CPPD crystals

Often intracellular

CPPD birefringence

Positive birefringence appearing blue when parallel

Cause of pseudogout

Cartilage degeneration and calcium deposition

Hydroxyapatite crystals

Basic calcium phosphate crystals

Hydroxyapatite association

Degenerative cartilage disease

Hydroxyapatite visibility

Too small to see under polarized light

Cholesterol crystals

Associated with corticosteroid injections

Calcium oxalate crystals

Seen in renal dialysis patients

Synovial glucose

Normally similar to blood glucose

Decreased synovial glucose

Seen in inflammatory and septic arthritis

Synovial glucose testing

Must be run simultaneously with blood glucose

Synovial lactate

Differentiates septic from non-septic arthritis

Elevated synovial lactate

Greater than 250 milligrams per deciliter suggests septic arthritis

False elevated synovial lactate

May be seen in rheumatoid arthritis

Synovial protein

Limited diagnostic value

Synovial uric acid

Elevated in gout if crystals are not detected

Common causes of septic arthritis

Staphylococcus, Streptococcus, Neisseria gonorrhoeae

Gram stain synovial fluid

Rapid presumptive test for infection

Culture synovial fluid

Definitive diagnosis of septic arthritis

Non-inflammatory joint disease

Degenerative joint disease with low WBC count

Inflammatory joint disease

Rheumatoid arthritis or lupus with elevated WBCs

Crystal-induced arthritis

Gout or pseudogout with very high WBCs and crystals

Septic arthritis

Bacterial infection with extremely high WBCs and neutrophils

Hemorrhagic joint disorder

Trauma or coagulation deficiency with RBCs present