joint fluid analysis

Joint Fluid Analysis

Definition

Joint fluid analysis, also called synovial fluid analysis, or arthrocentesis, is a procedure used to assess joint-related abnormalities, such as in the knee or elbow.

Purpose

The purpose of a joint fluid analysis is to identify the cause of swelling in the joints, to relieve pain and distention from fluid accumulation in the joint, and to diagnose certain types of arthritis and inflammatory joint diseases. The test is also a method to determine whether an infection, either bacterial or fungal, exists within the joint.

Precautions

Joint fluid analysis should not be performed on any patient who is uncooperative, especially if the patient cannot or will not keep the joint immobile throughout the procedure. Patients with certain infections should be excluded from the procedure, particularly those who have a local infection along the proposed needle track. The joint space should be accessible. Therefore, a poorly accessible joint space, such as in hip aspiration in an obese patient, should not be subject to this procedure.

Description

The test is also called arthrocentesis, joint tap, and closed joint aspiration. Normal synovial fluid is a clear or pale-yellow fluid found in small amounts in joints, bursae (fluid-filled sac found on points of friction, like joints), and tendon sheaths. The procedure is done by passing a needle into a joint space and sucking out (aspirating) synovial fluid for diagnostic analysis. When the sample is sent to the laboratory, the fluid is analyzed for color, clarity, quantity, and chemical composition. It is also examined microscopically to check for the presence of bacteria and other cells.The procedure takes about 10 minutes. Prior to the procedure, any risks that are involved should be explained to the patient. No intravenous pain medications or sedatives are required, although the patient will be given a local anesthetic.The patient is asked to lie on their back and remain relaxed. The local anesthetic, typically an injection of lidocaine, is then administered. The clinician is usually seated next to the patient. Then the clinician marks exactly where the needle is to enter. As the needle enters the joint, a "pop" may be felt or heard. This is normal. Correct placement of the needle in the joint space is normally painless. At this point, the clinician slowly drains some of the fluid into the syringe. The needle is then withdrawn and adhesive tape is placed over the needle site.

Preparation

Glucose, or sugar, in the joint can be a signal of arthritis. If the clinician will be doing a glucose test, the patient will be asked to fast for 6-12 hours preceding the procedure. If not, there is no special preparation required for a joint fluid analysis.

Aftercare

Some post-procedural pain may be experienced. For this reason, the patient should arrange to be driven home by someone else. Aftercare of the joints will depend on the results of the analysis.

Risks

While joint fluid analysis is generally a safe procedure, especially when performed on a large, easily accessible joint, such as the knee, some risks are possible. Some of the complications to the procedure, although rare, include infection at the site of the needle stick, an accumulation of blood (hematoma) formation, local pain, injury to cartilage, tendon rupture, and nerve damage.

Normal results

The results of a normal joint fluid analysis include fluid of a clear or pale-yellow color and the absence of bacteria, fungus, and other cells, such as white blood cells.

Abnormal results

The results of an abnormal joint fluid analysis include fluid that is turbid, or cloudy. Also, white blood cells and other blood cells may be found, from which the clinician can make a diagnosis and arrive at a treatment for the joint problem. An abnormal result can indicate an infection caused by a bacteria, or tuberculosis. Or, there might be inflammation that is caused by gout, rheumatoid arthritis, or osteoarthritis.

Resources

Books

Arnold, William J., and Robert W. Ike. "Specialized Procedures in the Management of Patients with Rheumatic Diseases." In Cecil Textbook of Medicine, edited by James B. Wyngaarden, et al. Philadelphia: W. B. Saunders Co., 1996.

Key terms

Aspirate — The removal by suction of a fluid from a body cavity using a needle.Bursae — A closed sac lined with a synovial membrane and filled with fluid, usually found in areas subject to friction, such as where a tendon passes over a bone.Hematoma — A localized mass of blood that is confined within an organ or tissue.Synovial fluid — A transparent lubricating fluid secreted in a sac to protect an area where a tendon passes over a bone.

joint fluid analysis

See Synovial fluid analysis.

Synovial Fluid Analysis

Synonym/acronym: Arthrocentesis, joint fluid analysis, knee fluid analysis.

Common use

To identify the presence and assist in the management of joint disease related to disorders such as arthritis and gout.

Specimen

Synovial fluid collected in a red-top tube for antinuclear antibodies (ANAs), complement, crystal examination, protein, rheumatoid factor (RF), and uric acid; sterile (red-top) tube for microbiological testing; lavender-top (EDTA) tube for mucin clot/viscosity, complete blood count (CBC) and differential; gray-top (sodium fluoride [NaFl]) tube for glucose; green-top (heparin) tube for lactic acid and pH.

Normal findings

(Method: Macroscopic evaluation of appearance; spectrophotometry for glucose, lactic acid, protein, and uric acid; Gram stain, acid-fast stain, and culture for microbiology; microscopic examination of fluid for cell count and evaluation of crystals; ion-selective electrode for pH; nephelometry for RF and C3 complement; indirect fluorescence for ANAs).

Test	Normal Result
Color	Colorless to pale yellow
Clarity	Clear
Viscosity	High
ANA	Parallels serum level
C3	Parallels serum level
Glucose	Less than 10 mg/dL of blood level
Lactic acid	5–20 mg/dL
pH	7.2–7.4
Protein	Less than 3 g/dL
RF	Parallels serum level
Uric acid	Parallels serum level
Crystals	None present
RBC count	None
WBC count	Less than 200/microL
Neutrophils	Less than 25%
WBC morphology	No abnormal cells or inclusions
Gram stain and culture	No organisms present
AFB smear and culture	No AFB present

AFB = acid-fast bacilli; ANA = antinuclear antibodies; C3 = complement; RBC = red blood cell; RF = rheumatoid factor; WBC = white blood cell.

Description

Synovial fluid analysis is performed via arthrocentesis, an invasive procedure involving insertion of a needle into the joint space. Synovial effusions are associated with disorders or injuries involving the joints. The most commonly aspirated joint is the knee, although samples also can be obtained from the shoulder, hip, elbow, wrist, and ankle if clinically indicated. Joint disorders can be classified into five categories: noninflammatory, inflammatory, septic, crystal-induced, and hemorrhagic. The mucin clot test is used to correlate the qualitative assessment of synovial fluid viscosity with the presence of hyaluronic acid. The test is performed by mixing equal amounts of synovial fluid and 5% acetic acid solution on a glass slide and grading the ropiness of the subsequent clot as good, fair, or poor. Long, ropy strands are seen in normal synovial fluid.

This procedure is contraindicated for

N/A

Indications

Administration of anti-inflammatory medications by injection
Assist in the diagnosis of arthritis
Assist in the evaluation of joint effusions
Assist in the diagnosis of joint infection
Differentiate gout from pseudogout

Potential diagnosis

Fluid values increased in

Acute bacterial infection: Elevated WBC count with marked predominance of neutrophils (greater than 90% neutrophils), positive Gram stain, positive cultures, possible presence of rice bodies, increased lactic acid (produced by bacteria), and complement levels paralleling those found in serum (may be elevated or decreased) Gout: Elevated WBC count with a predominance of neutrophils (90% neutrophils), presence of monosodium urate crystals, increased uric acid, and complement levels paralleling those of serum (may be elevated or decreased) Osteoarthritis, traumatic arthritis degenerative joint disease: Elevated WBC count with less than 25% neutrophils and the presence of cartilage cells Pseudogout: Presence of calcium pyrophosphate crystals Rheumatoid arthritis: Elevated WBC count with a predominance of neutrophils (greater than 70% neutrophils), presence of ragocyte cells and possibly rice bodies, presence of cholesterol crystals if effusion is chronic, increased protein, increased lactic acid, and presence of rheumatoid factor Systemic lupus erythematosus (SLE): Elevated WBC count with a predominance of neutrophils, presence of SLE cells, and presence of antinuclear antibodies Trauma, joint tumors, or hemophilic arthritis: Elevated RBC count, increased protein level, and presence of fat droplets (if trauma involved) Tuberculous arthritis: Elevated WBC count with a predominance of neutrophils (up to 90% neutrophils), possible presence of rice bodies, presence of cholesterol crystals if effusion is chronic, in some cases a positive culture and smear for acid-fast bacilli (results frequently negative), and lactic acid

Fluid values decreased in (analytes in parentheses are decreased)

Acute bacterial arthritis (glucose and pH) Gout (glucose) Rheumatoid arthritis (glucose, pH, and complement) SLE (glucose, pH, and complement) Tuberculous arthritis (glucose and pH)

Critical findings

Positive culture findings in any sterile body fluid.
Note and immediately report to the health-care provider (HCP) positive culture results, if ordered, and related symptoms.
It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.
Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

Interfering factors

Blood in the sample from traumatic arthrocentesis may falsely elevate the RBC count.
Undetected hypoglycemia or hyperglycemia may produce misleading glucose values.
Refrigeration of the sample may result in an increase in monosodium urate crystals secondary to decreased solubility of uric acid; exposure of the sample to room air with a resultant loss of carbon dioxide and rise in pH encourages the formation of calcium pyrophosphate crystals.

Nursing Implications and Procedure

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this procedure can assist in assessing joint health.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
Obtain a history of the patient’s immune and musculoskeletal systems, especially any bleeding disorders and other symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Note any recent procedures that can interfere with test results.
Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
Obtain a list of the patient’s current medications, anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Such products should be discontinued by medical direction for the appropriate number of days prior to a surgical procedure.
Review the procedure with the patient. Inform the patient that it may be necessary to remove hair from the site before the procedure. Address concerns about pain and explain that a sedative and/or analgesia will be administered to promote relaxation and reduce discomfort prior to needle insertion through the joint space. Explain that any discomfort with the needle insertion will be minimized with local anesthetics and systemic analgesics. Explain that the anesthetic injection may cause an initial stinging sensation. Explain that, after the skin has been anesthetized, a large needle will be inserted through the joint space, and a “popping” sensation may be experienced as the needle penetrates the joint. Inform the patient that the procedure is performed by a health-care provider (HCP) specializing in this procedure. The procedure usually takes approximately 20 min to complete.
Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
Note that there are no fluid restrictions unless by medical direction. Fasting for at least 12 hr before the procedure is recommended if fluid glucose measurements are included in the analysis. Instruct the patient to avoid taking anticoagulant medication or to reduce dosage as ordered prior to the procedure. Protocols may vary among facilities.
Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

Intratest

Potential complications: N/A
Ensure that the patient has complied with dietary and medication restrictions and pretesting preparations; assure that food has been restricted for at least 12 hr prior to the procedure. Ensure that anticoagulant medications and aspirin have been withheld, as ordered.
Assemble the necessary equipment, including an arthrocentesis tray with solution for skin preparation, local anesthetic, a 20-mL syringe, needles of various sizes, sterile drapes, and sterile gloves for the tests to be performed.
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement during the local anesthetic and the procedure.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date and time of collection, and site location, especially, right or left knee, shoulder, hip, elbow, wrist, or ankle.
Assist the patient into a comfortable sitting or supine position, as appropriate.
Use clippers to remove hair from the site prior to the administration of general or local anesthesia, cleanse the site with an antiseptic solution, and drape the area with sterile towels.
After the local anesthetic is administered, the needle is inserted at the collection site, and fluid is removed by syringe. Manual pressure may be applied to facilitate fluid removal.
If medication is injected into the joint, the syringe containing the sample is detached from the needle and replaced with the one containing the drug. The medication is injected with gentle pressure. The needle is withdrawn, and digital pressure is applied to the site for a few minutes. If there is no evidence of bleeding, a sterile dressing is applied to the site. An elastic bandage can be applied to the joint.
Monitor the patient for complications related to the procedure (allergic reaction, anaphylaxis).
Place samples in properly labeled specimen containers and promptly transport the specimens to the laboratory for processing and analysis. If bacterial culture and sensitivity tests are to be performed, record on the specimen containers any antibiotic therapy the patient is receiving.

Post-Test

Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
Instruct the patient to resume usual diet and medications, as directed by the HCP.
After local anesthesia, monitor vital signs and compare with baseline values. Notify the HCP if temperature is elevated. Protocols may vary among facilities.
Observe/assess puncture site for bleeding, bruising, inflammation, and excessive drainage of synovial fluid approximately every 4 hr for 24 hr and daily thereafter for several days.
Instruct the patient to report excessive pain, bleeding, or swelling to the requesting HCP immediately. Report to HCP if severe pain is present or the patient is unable to move the joint.
Observe/assess for nausea and pain. Administer antiemetic and analgesic medications as needed and as directed by the HCP.
Instruct the patient to apply an ice pack to the site for 24 to 48 hr.
Administer antibiotics, as ordered, and instruct the patient in the importance of completing the entire course of antibiotic therapy even if no symptoms are present.
Recognize anxiety related to test results, and be supportive of impaired activity related to anticipated chronic pain resulting from joint inflammation, impairment in mobility, musculoskeletal deformity, and loss of independence. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services, as appropriate. Provide contact information, if desired, for the American College of Rheumatology (www.rheumatology.org) or for the Arthritis Foundation (www.arthritis.org).
Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Instruct the patient or caregiver to handle linen and dispose of dressings cautiously, especially if septic arthritis is suspected. Instruct the patient to avoid excessive use of the joint for several days to prevent pain and swelling. Instruct the patient to return for a follow-up visit as scheduled. Answer any questions or address any concerns voiced by the patient or family.
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include antibodies anti-cyclic citrullinated, ANA, arthrogram, arthroscopy, BMD, bone scan, CRP, cholesterol, CBC, CBC WBC count and differential, ESR, MRI musculoskeletal, radiography bone, RF, synovial fluid analysis, and uric acid.
Refer to the Immune and Musculoskeletal systems tables at the end of the book for related tests by body system.