Synovial Fluid

purpose of synovial fluid

• cushions joints

• provides nutrients to cartilage

• reduces friction

composition of synovial fluid

ultrafiltrate of plasma with no high MW molecules

viscosity of synovial fluid

secretion of synovial membrane fluid

viscous from proteins and hyaluronic acid

arthrocentesis

needle aspiration into joints (usually knee)

normal volume of synovial fluid in joints

0.1-3.5 mL

how much synovial fluid is collected for examination?

4-5 mL per tube

what is in the collection tubes for chemistry and immunology?

no anticoag

what is in the collection tubes for hematology?

either sodium heparin or liquid EDTA

• cannot use powedered anticoagulants when observing crystals 

what type of collection tube should be used for microbio testing?

sterile

what is the normal appearance of synovial fluid?

clear and pale yellow

significance of deep yellow color

inflammation

significance of green color

infection

significance of red/brown color

blood

what causes turbidity in synovial fluid?

WBCs or crystals 

how is viscosity measured?

the string test

• performed bed side 

• string should form 4-6 cm long

what causes decreased viscosity?

any type of arthritis 

clotting test for synovial fluid

in a normal sample adding acetic acid should form a clot 

what causes abnormal clotting in synovial fluid?

the presence of fibrinogen

• damage to synovial membrane 

• contamination from PB

• traumatic tap

what reagent is used during cell counts?

saline or hyaluronidase (digests hyaluronic acid)

what methods exist for cell counts in synovial fluid?

automated or hemacytometer

normal cell values for synovial fluid

• less than 200 nucleated cells

• less than 2000 RBCs

what is the normal differential of cells in synovial fluid?

primarily mononuclear cells (monos, macros)

less than 25% PMNs 

less than 25% lymphocytes 

significance of increase in neutrophils

bacterial infection or crystal disorder

significance of increase in lymphocytes

nonseptic inflammation (RA)

significance of reiter cells

macros that phagocytized PMNs, usually after an infection

significance of RA cells

“ragocytes”

PMNs with cyoplasmic granules of RF (protein aggregates)

significance of LE cells

lupus cells; PMNs with large inclusions 

nucleus is damaged

seen with SLE

gout

form of arthritis 

• imparied metabolism of NA

• decreased renal excretion of uric acid 

• monosodium urate crystals

• usually found in big toe

monosodium urate crystals (MSU)

• inside neutrophils 

• look like needles 

• strong negative bifringence 

• yellow is parallel 

• blue is perpendicular 

pseudogout/chondrocalcinosis

• often accumulates in knee

• seen with metabolic disorders like diabetes

• calcium phyrophostphate dihydrate crystals

calcium phyrophostphate dihydrate crystals (CPPD)

• weak positive bifringence 

• yellow is perpendicular 

• blue is parallel

significance of elevated protein levels

RA

significance of low glucose levels

inflammation or sepsis 

what microbio tests are performed?

gram stains and cultures