Understanding Your Laboratory Test: What It Is, How the Sample Is Collected, and Why Your Doctor May Order It
This test counts basophils (a type of white blood cell) in the fluid from a joint to help diagnose joint problems.
{"Measures basophils in joint (synovial) fluid","Collected through a procedure called arthrocentesis (joint fluid aspiration)","Helps diagnose infections, arthritis, and inflammatory joint conditions","Results are typically reported as a percentage of white blood cells","Often performed alongside other synovial fluid tests"}
Key facts at a glance
- LOINC
- 57836-9
- Short code
- SYNBASO
- Synonyms
- Basophils NFr Snv Manual
- Category
- chemistry
- Sample
- fluid
- Container
- Sterile, heparinized or EDTA-containing tube; plain sterile tube acceptable for cell count. Lavender-top (EDTA) tube preferred for cell differential preservation.
- Units
- N/A
- Ref low
- 0
- Ref high
- 1
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- manual-count
- CPT
- 89051
- SNOMED
- 416723004
- Specimen volume
- 1-5 mL of synovial fluid (minimum 0.5 mL for cell count)
- Stability
- Specimen should be analyzed within 1 hour of collection for optimal cell count accuracy. If delayed, refrigerate at 2-8°C and analyze within 24 hours; note that cell viability decreases over time.
- Hemolysis max
- 300
- TAT
- 1–4 hours
- Order
- routine
What is this test, what does it measure, and why is it important for my health?
The Synovial Fluid Basophil Count is a laboratory test that measures the number and percentage of basophils in the synovial fluid — the clear, viscous fluid that lubricates and cushions joints. Basophils are a type of white blood cell (leukocyte) that play a role in the body's immune response, particularly in allergic reactions and inflammation. This test is performed manually under a microscope by a trained laboratory professional who examines a stained sample of the joint fluid.
How is the sample for this test collected, and what can I expect during the collection process?
The sample is collected through a procedure called arthrocentesis, also known as joint aspiration. A healthcare provider inserts a thin needle into the joint space to withdraw synovial fluid. This procedure is typically performed in a clinic or hospital setting. The area is first cleaned and numbed with a local anesthetic to minimize discomfort. The extracted fluid is then sent to a laboratory for analysis, where specialists examine it under a microscope to identify and count different types of cells, including basophils.
Why might my doctor order this test for me, and what conditions can it help diagnose or monitor?
Your doctor may order this test if you have symptoms of joint problems such as swelling, pain, stiffness, warmth, or limited movement. It helps differentiate between various causes of joint inflammation, including different types of arthritis (such as rheumatoid arthritis, gout, or septic arthritis), joint infections, or traumatic joint injuries. The basophil count, along with other cell counts and tests performed on the synovial fluid, provides important clues about what's causing your joint symptoms.
Reference range
Basophils are not typically present in normal synovial fluid. The total leukocyte count in normal synovial fluid is <200 cells/µL with a predominance of mononuclear cells (<25% polymorphonuclear cells). Basophils are reported as a percentage of the total leukocyte differential.N/A
No special patient preparation required. Synovial fluid collection is performed by arthrocentesis under sterile conditions by a qualified healthcare provider. Inform the clinician of any anticoagulant use or bleeding disorders prior to the procedure.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated basophils in synovial fluid may indicate inflammatory conditions such as rheumatoid arthritis, allergic arthritis, or other types of inflammatory arthritis. Basophils contain histamine and other inflammatory mediators, so their presence in increased numbers suggests an active inflammatory or allergic process within the joint. Very high white blood cell counts with predominance of neutrophils may suggest a bacterial infection (septic arthritis), which requires urgent treatment. The basophil count is interpreted alongside other findings like crystal analysis (for gout or pseudogout), glucose, protein levels, and Gram stain results to form a complete picture of joint health.
Frequently asked questions
Does the test hurt?
How long does it take to get results?
Are there any risks to having this test?
Do I need to prepare for the test?
What do abnormal results mean?
Sources
- 1
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy