SIP blogging

Hello to all, this week I will be blogging on body fluids for examination. Body cavity fluids other than blood or urine are referred as extravascular fluids and they are:
1.) Cerebrospinal (around the brain and spinal cords)
2.) Synovial (around the joints)
3.) Pleural (around the lungs)
4.) Peritoneal (around the abdominal and pelvis cavities)

This blog i going to talk about synovial fluid.

Normal synovial fluid is clear straw-coloured or pale yellow fluid found in small amount in joints and tendons sheaths. It is an ultrafiltrate of plasma plus a mucopolysaccharide, produced by the lining synovial cells which make the fluid thick and viscous. Normal volume of fluid in knee joints is about 3.5ml.

Function of synovial fluid is to lubricate the joint space, transport nutrients to the articular cartilage, remove waste and debris from joint and medium for leucocytes to circulate and phagocytize debris.

Clinical significance for synovial fluid analysis is in the differential diagnosis of swollen joint: distinguish crystal-inducing disease from septic joints.

Sample Collection/Preparation
Synovial fluid is collected by aspiration of fluid from the joint space with a needle. Due to cells are easily destroyed and glucose may also undergo glycolysis on standing, thus the analysis of fluid must be done immediately once received.

Laboratory Analysis of Synovial Fluid
1. Appearance

First, state the appearance and clarity of the fluid received. Synovial fluid can be described as:
- Straw colour or pale yellow and clear is the normal appearance of synovial fluid
- Turbid or purulent sample is seen in bacterial infection or high leucocytes count.
- Blood-stained
- Chylous fluid refer to having a characteristics milky, opaque appearance which remains in the supernatant after centrifugation, which is caused by lymphatic leakage or obstruction.
If the fluid is blood stained or turbid, spun it down and state the appearance of the supernatant.

2. Cell Count and WBC Differential

A cell-count with differential would aid in making the diagnosis as bacterial infections will have a predominance of neutrophils while viral, fungues and mycobacterial infections may have a predominance of lymphocytes or show a mixed inflammatory response.

If the effusion is predominantly neutrophils, an acute inflammatory process is the cause and differential count showing essentially all lymphocytes suggests a chronic process.

3. Glucose

Fluid glucose is reduced due to bacterial, increased WBCs or infiltration with malignant cells the reduction is the result of the metabolic requirement of the infecting organisma and of the inflammatory cells as well as the tumour cells.

4. Total Protein

Total protein is abnormally raised in: infection, malignant infiltration, chronic inflammatory conditions or traumatic tap (false positive)

Differentiation of exudate and transudate fluid

5. Crystals

The 3 most common types of crystals present in the joint fluid are:
- Monosodium urate
- Calcium pyrophosohate
- Cholesterol

Monosodium Urate Crystals(MSU):
These crystals are needle shaped, double refractile of 8-10um long, negatively birefringent and soluble in water. They are associated with gout and may be intracellular. MSU crystals are negatively birefringent and when aligned parallel to the compensator will show a yellow colour and when turned perpendicular to the compensator the colour change to blue.

Calcium Pyrophosphate Dihydrate Crystals(CPPD):
These are associated with pseudogout, which most frequently involves the wrists and knees. These crystals have various shapes but usually rhomboid in shape and are positively birefringent. They are broader than uric acid crystals and up to 25um long, have a line running through them. The crystals are blue in colour when parallel to the compensator and yellow when perpendicular to it.

Cholesterol Crystal:
Cholesterol crystals have a characteristics notched-plate and birefringent. They are present in chronic inflamed joints such as rheumatoid arrthritis. In pseudogout, serum uric acid is normal while serum uric acid is high in gout. Cholesterol crystals may be found in any chronic effusion.


6. Summary:

Normal Synovial Fluid
- Clear , yellow fluid which does not clot spontaneously
- UP to 200 WBC/uL of which less than 25% are neutrophils
- No Crystals
- Total protein: 18g/L
- Glucose level is similar to serum glucose level

Juexiu
tg02