synovial fluid analysis


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synovial fluid analysis

Lab medicine The evaluation of SF obtained by aspiration from the knee, shoulder, hip, elbow, less commonly from another joint; SFA is commonly performed on younger Pts to detect infection–eg,
with staphylococcus or TB and in older Pts to categorize type of inflammation–eg, rheumatoid arthritis, pseudogout, exclude gout
Synovial fluid analysis*
Type   Appearance  Glucose  WBC/mL PMNs Viscosity  
Normal Clear yellow < 10 mg/dL < 200/µL < 25% ↑
Noninflammatory  Clear yellow < 10 mg/dL < 2000/µL < 25% ↑
Inflammatory  Slightly turbid < 20 mg/dL <5000/µL < 50% ↓
Septic-mild Turbid < 40 mg/dL <50,000/µL  50-90% ↓
Septic-severe Turbid/purulent> 20 mg/dL >50,000/µL > 90% ↓
*after JB Henry, Ed, Clinical Diagnosis & Management by Laboratory Methods, 18th edition, WB Saunders, 1991
‡Synovial fluid and blood difference

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).
TestNormal Result
ColorColorless to pale yellow
ClarityClear
ViscosityHigh
ANAParallels serum level
C3Parallels serum level
GlucoseLess than 10 mg/dL of blood level
Lactic acid5–20 mg/dL
pH7.2–7.4
ProteinLess than 3 g/dL
RFParallels serum level
Uric acidParallels serum level
CrystalsNone present
RBC countNone
WBC countLess than 200/microL
NeutrophilsLess than 25%
WBC morphologyNo abnormal cells or inclusions
Gram stain and cultureNo organisms present
AFB smear and cultureNo 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.
References in periodicals archive ?
Yet surveys show that most rheumatologists don't routinely perform synovial fluid analysis, opting instead to hang their diagnosis on clinical features and demonstration of hyperuricemia.
Baseline MRI's and synovial fluid analysis for each patient performed just prior to the start of the injections, will be repeated at week 12 and compared to baseline to explore whether there are additional clinical benefits beyond pain relief and improved function.
The role of immunological tests in routine synovial fluid analysis.