Arthrocentesis with synovial fluid analysis
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p115-118
2025-10-28
52
Type of test Fluid analysis
Normal findings
Test explanation and related physiology
Arthrocentesis is performed to establish the diagnosis of joint infection, arthritis, crystal-induced arthritis (gout and pseudogout), synovitis, or neoplasms involving the joint. This procedure is also used to identify the cause of joint inflammation or effusion and to inject antiinflammatory medications (usually corticosteroids) into a joint space.
Arthrocentesis is performed by inserting a sterile needle into the joint space of the involved joint to obtain synovial fluid for analysis. Synovial fluid is a liquid found in small amounts within the joints. Aspiration (withdrawal of the fluid) may be performed on any major joint such as the knee, shoulder, hip, elbow, wrist, or ankle.
The fluid sample is examined. Normal joint fluid is clear, straw colored, and quite viscous. Viscosity is reduced in patients with inflammatory arthritis. Viscosity can be roughly estimated by forcing some synovial fluid from a syringe. Fluid of normal viscosity forms a “string” more than 5 cm long (string sign); fluid of low viscosity as seen in inflammation drips in a manner similar to water. A Gram stain and culture of the fluid is usually performed.
The mucin clot test correlates with the viscosity and is an estimation of hyaluronic acid–protein complex integrity. This test is performed by adding acetic acid to joint fluid. The formation of a tight, ropy clot indicates qualitatively good mucin and the presence of adequate molecules of intact hyaluronic acid. Hyaluronic acid can be directly quantified. The mucin clot is poor in quality and quantity in the presence of an inflammatory joint disease such as rheumatoid arthritis (RA). By itself, synovial fluid should not spontaneously form a fibrin clot (clot without the addition of acetic acid) because normal joint fluid does not contain fibrinogen. If, however, bleeding into the joint (from trauma or injury) has occurred, the synovial fluid will clot.
The synovial fluid glucose value is usually within 10 mL/dL of the fasting serum glucose value. For proper interpretation, the synovial fluid glucose and serum glucose samples should be drawn simultaneously after the patient has fasted for 6 hours. The synovial fluid glucose level falls with increasing severity of inflammation. Although lowest in septic arthritis, a low synovial glucose level also may be seen in patients with rheumatoid arthritis. The synovial fluid is also tested for protein, uric acid, and lactate levels. Increased uric acid levels indicate gout. Increased protein and lactate levels indicate bacterial infection or inflammation.
Cell counts are also performed on the synovial fluid. Normally the joint fluid contains less than 150 WBCs/mm3 and 2000 RBCs/mL. An increased WBC count with a high percentage of neutrophils (over 75%) supports the diagnosis of acute bacterial infectious arthritis. Leukocytes can also occur in other conditions such as acute gouty arthritis and rheumatoid arthritis. The differential WBC count, however, will indicate monocytosis or lymphocytosis with these later-mentioned diseases.
Bacterial and fungal cultures are usually requested and per formed when infection is suspected. The administration of antibiotics before arthrocentesis may diminish growth of bacteria from synovial fluid cultures and confound results. Smears for acid-fast stains for tubercle bacilli are also performed on the synovial fluid. Synovial fluid is also examined under polarized light for the presence of crystals, which permits differential diagnosis between gout and pseudogout.
The synovial fluid is also analyzed for complement levels. Complement levels are decreased in patients with systemic lupus erythematosus, rheumatoid arthritis, or other immunologic arthritis. These decreased joint complement levels are caused by consumption of the complement induced by the antigen-antibody immune complexes within the joint cavity.
One of the most important tests routinely performed on synovial fluid is the microscopic examination for crystals. For example, urate crystals indicate gouty arthritis. Calcium pyrophosphate crystals are found in pseudogout. Cholesterol crystals occur in rheumatoid arthritis.
Contraindications
• Patients with skin or wound infections near the needle puncture because of the risk of sepsis Potential complications
• Joint infection
• Hemorrhage in the joint area
Procedure and patient care
Before
* Explain the procedure to the patient.
• Obtain an informed consent if indicated.
• The physician may request that the patient be kept NPO after midnight on the day of the test.
During
• Have the patient lie on his or her back with the joint fully extended.
• Note the following procedural steps:
1. The skin is locally anesthetized to minimize pain.
2. The area is aseptically cleansed, and a needle is inserted through the skin and into the joint space.
3. Fluid is obtained for analysis. If a corticosteroid or other medications (e.g., antibiotics) are to be administered, a syringe containing the steroid preparation is attached to the needle, and the drug is injected.
4. The needle is removed, and a wrap dressing may be applied to the site.
5. Sometimes a peripheral venous blood sample is taken to compare chemical tests on the blood with chemical studies on the synovial fluid.
• Note that a physician performs this procedure in an office or at the patient’s bedside in approximately 20 minutes.
* Tell the patient that the only discomfort associated with this test is the injection of the local anesthetic.
• Be aware that joint-space pain may worsen after fluid aspiration, especially in patients with acute arthritis.
After
* Assess the joint for any pain, fever, or swelling. Teach the patient to look for signs of infection at home.
* Apply ice to decrease pain and swelling and instruct the patient to continue this at home.
* Tell the patient to avoid strenuous use of the joint for the next several days. Teach the patient to walk on crutches if indicated.
* Instruct the patient to look for signs of bleeding into the joint (significant swelling, increasing pain, or joint weakness).
* Instruct the patient not to drive until it is approved by the physician.
Abnormal findings
- Infection
- Osteoarthritis
- Synovitis
- Neoplasm Joint effusion
- Septic arthritis
- Systemic lupus erythematosus
- Rheumatoid arthritis
- Gout
- Pseudogout
الاكثر قراءة في التحليلات المرضية
اخر الاخبار
اخبار العتبة العباسية المقدسة
