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Background
The two most prevalent crystalline arthropathies are gout and pseudogout. They are caused by formation of calcium pyrophosphate dihydrate (CPPD) and monosodium urate (MSU). This formation can lead to pain, inflammation and destruction of joint. These diseases are diagnosed clinically. Other crystals, like basic calcium phosphate (BCP) crystals and calcium oxalate crystals, are also present in synovial fluid. BCP crystals are linked to calcific periarthritis and tendinitis. Calcium oxalate crystals are linked with chronic renal failure or primary hyperoxaluria.
Microscopic examination of joint fluid is the standard criteria to diagnose the disease. These crystals are found on other inflammatory arthritides like rheumatoid arthritis (RA). It is unclear the role of these crystals in these diseases.
Joint fluid crystal test is an important laboratory test which is used to diagnose and manage the crystal induced arthropathies. These diseases may include pseudogout, gout, and other crystalline arthropathies. The crystals which are present in synovial fluid may cause acute to chronic inflammation, swelling, pain, and joint damage.
Joint fluid analysis is important to diagnose crystal-induced synovitis and septic arthritis. Septic arthritis is an emergency disease because of the risk of pyogenic infection, which destroys the joint. Purulent fluid needs antibiotic treatment, although the gram stain is negative. About 25% of the cases of patients with gonococcal arthritis have positive synovial fluid gram stains.
Crystal synovitis includes concomitant infection. Gram stain and culture must be done. Calcium salts is linked with synovitis and calcium oxalate crystals found in synovial effusions of patients who are going for hemodialysis.
Indications/Applications
This test is used in joint conditions like gout, arthritis, and other diseases.
If you have joint symptoms like:
Swelling
Redness
Pain
Fluid buildup
It is also performed in the conditions like lupus, RA, hemophilia, osteoarthritis
Reference Range
A typical joint fluid aspirate does not include crystals, so the test result is negative.
Other parameters like
Synovial color – Pale yellow
Synovial appearance – Clear
Synovial red blood cell count – 0
Synovial white blood cell count – (0-150/mm3)
Synovial lymphocytes – 24%
Synovial neutrophils – 7%
Synovial macrophages – 10%
Synovial monocytes – 48%
Protein – 1 dL to 3 dL
Uric acid – 6 mg/dL to 8 mg/dL
Lactic acid dehydrogenase – < 25 mg/dL
Gram stain – -ve
Interpretation
Diagnosis of pseudogout and gout is clinical. They may be confirmed with the joint fluid analysis.
Gout
MSU crystals are negatively birefringent as they are thin, long, and pointed. These can be in tophi, within or outside the cell.
WBC counts are in inflammatory range of 10000/µL-20000/µL in synovial fluid.
Pseudogout
CPPD crystals are less sharp, short than MSU crystals and under polarized light they are positive birefringent. They are in or outside of the cell.
WBC counts in the inflammatory range of 10000/µL-200000/µL in synovial fluid.
Joint infection is different in both gout and pseudogout. The fluid must be sampled as sterile and send for culture and gram stain.
Calcific periarthritis and Milwaukee shoulder syndrome
BCP crystals are not visible under the normal light microscope. Visible by electric microscope.
Chronic renal failure or primary hyperoxaluria
Calcium oxalate crystals are envelope-shaped or bipyramidal and strong positive birefringence.
An increased WBC count indicates infection or other medical diseases.
An increased RBC count indicates bleeding disorder, injury.
Normal fluid is colorless or pale yellow, clear, free from fungi, bacteria, and viruses, and stringy.
Collection And Panels
Sample type: Synovial fluid from joint
Sample container: Sterile container like used for urinalysis
Sample collection method: Sterile needle aspiration
Sample volume: Minimum 1 mL
Considerations: Sterile sample collection allow fluid to send for culture depends on clinical suspensions for infection. It reduces the risk of bacteria into the joint.
Panels:
Gram stain and Culture and sensitivity – It is used to detect the bacterial infection in the joint.
Cell differentiation and cell count – Gives the information about the inflammation or infection.
Character and color – The appearance of fluid gives information about the underlying cause of the disease.
Glucose and Protein Levels – Decreased glucose levels and increased protein levels may indicate infection or inflammation.
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