Understanding Your Medical Test: What It Is, How It Is Performed, and Why You May Need It
This test checks for the presence of basophils (a type of white blood cell) in the fluid surrounding your joints.
{"Basophils are rare in normal joint fluid","Their presence may indicate inflammation or joint damage","The test uses a microscope to examine fluid drawn from the joint","Results help doctors diagnose conditions like arthritis or infections","The procedure is called arthrocentesis"}
Key facts at a glance
- LOINC
- 44041-2
- Short code
- BASSYN
- Synonyms
- Basophils Snv Ql Micro
- Category
- chemistry
- Sample
- fluid
- Container
- Sterile, heparinized collection tube or plain sterile tube without additives; lavender-top (EDTA) tube acceptable for cell counts
- Units
- N/A
- Ref low
- 0
- Ref high
- 1
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- microscopy-light
- CPT
- 89051
- SNOMED
- 44221000087104
- Specimen volume
- 1-5 mL of synovial fluid minimum; ideally 2-5 mL for complete analysis
- Stability
- Room temperature: 1 hour for optimal cell morphology; Refrigerated (2-8°C): up to 24 hours in EDTA tube. Cell counts should be performed as soon as possible, preferably within 1 hour of collection.
- Hemolysis max
- 300
- TAT
- 1–4 hours
- Order
- routine
This test is a diagnostic procedure that gives your healthcare provider important information about how your body is working. The results can help detect, monitor, or rule out certain health conditions so that you and your care team can make well-informed decisions about your treatment and overall care.
The Basophils in Synovial Fluid test examines joint fluid under a microscope to detect the presence of basophils. Basophils are a type of white blood cell that play a role in your body's immune response and inflammation. They are normally found in very small numbers or not at all in healthy joint (synovial) fluid.
The test is usually performed in a clinic, laboratory, or hospital setting by a trained member of your care team. Depending on the type of test, a small sample of blood, urine, or other body tissue may be collected, or a scanning device may be used. The procedure is typically quick, and most people can return to normal activities soon afterward.
A doctor will first withdraw a small amount of fluid from your joint using a thin needle. This procedure is called joint aspiration or arthrocentesis. The fluid is then placed on a slide and examined under a microscope to look for basophils and other cells. The entire process usually takes only a few minutes.
Your healthcare provider may recommend this test to help find the cause of symptoms you are having, to screen for a condition before it causes problems, or to monitor a health condition you already have. The results can guide treatment decisions and help show how well your current treatment plan is working for you.
Your doctor may order this test if you have joint pain, swelling, stiffness, or limited movement. It helps determine the cause of these symptoms and distinguish between different types of joint conditions, such as inflammatory arthritis, infection, or mechanical injury.
Reference range
Basophils are normally absent or present in very low numbers in synovial fluid (typically <1% of nucleated cells). Presence of basophils in synovial fluid is generally considered abnormal and may indicate inflammatory or allergic processes.N/A
No special patient preparation required. Synovial fluid collection (arthrocentesis) should be performed under sterile conditions by a qualified healthcare provider. Inform the physician of any bleeding disorders, anticoagulant use, or skin infections at the puncture site prior to the procedure.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Frequently asked questions
Is the joint aspiration procedure painful?
How long does it take to get results?
Are there any risks associated with this test?
Do I need to prepare for the test?
Sources
- 1
- 2
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