Understanding Your Medical Test: What It Is, How It Is Performed, and Why Your Doctor May Recommend It
This test measures the number of basophils, a type of white blood cell, in the fluid surrounding your joints.
{"Basophils are white blood cells that play a role in inflammation and allergic responses","This test helps doctors evaluate joint inflammation and conditions like arthritis","Abnormal results may indicate infection, inflammation, or other joint conditions"}
Key facts at a glance
- LOINC
- 35074-4
- Short code
- SYNBASO
- Synonyms
- Basophils # Snv
- Category
- chemistry
- Sample
- fluid
- Container
- Sterile, heparinized (sodium or lithium heparin) collection tube or plain sterile tube; lavender-top (EDTA) tube acceptable for cell counts; fluoride-oxalate tube should be avoided
- Units
- N/A
- Ref low
- 0
- Ref high
- 0
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Manual microscopic differential cell count using hemocytometer and stained cytocentrifuge preparation (Wright-Giemsa or similar stain)
- CPT
- 89051
- SNOMED
- 442780000
- Specimen volume
- 1-3 mL of synovial fluid (minimum 0.5 mL for cell count); larger volumes preferred for comprehensive analysis
- Stability
- Specimen should be analyzed within 1 hour of collection for optimal cell morphology; if delayed, refrigerate at 2-8°C and analyze within 4 hours; do not freeze for cell count purposes
- Hemolysis max
- 300
- TAT
- 1–4 hours
- Order
- routine
This test is a medical procedure that helps your doctor evaluate how your body is working, look for signs of illness, and gather important information to guide decisions about your care and treatment options.
The basophil count in synovial fluid test measures the number of basophils in the fluid that cushions your joints. Synovial fluid is a thick, slippery liquid that helps your joints move smoothly. Basophils are a type of white blood cell that are part of your body's immune system and help fight infections and regulate inflammation.
Your healthcare provider will explain each step before the test begins. Depending on the type of test, a small sample of blood, urine, or other tissue may be collected, or imaging equipment may be used. The procedure is usually quick, and most people can return home the same day.
A healthcare provider will collect a small sample of synovial fluid from your joint using a needle in a procedure called joint aspiration or arthrocentesis. The fluid is then sent to a laboratory where specialists count the number of basophils under a microscope or using automated equipment.
Your doctor may recommend this test to confirm or rule out a medical condition, monitor an ongoing health problem, check how well a current treatment is working, or screen for issues before symptoms appear. The results help your care team choose the best plan for you.
Your doctor may order this test if you have joint pain, swelling, or stiffness. It helps determine the cause of your joint problems, such as infection, inflammatory conditions like rheumatoid arthritis, gout, or other disorders affecting your joints.
Reference range
Basophils are normally absent or rarely present in synovial fluid (typically 0 cells/µL); basophils are generally not reported as a standard component of synovial fluid differentialN/A
No fasting required. Synovial fluid collection (arthrocentesis) is performed by a qualified healthcare provider under sterile conditions. The puncture site is cleaned with antiseptic, and local anesthesia may be administered. Patient should inform the provider of any bleeding disorders, anticoagulant use, or skin infections at the joint site prior to the procedure.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated basophil levels in synovial fluid may indicate inflammatory conditions such as rheumatoid arthritis, psoriatic arthritis, or other autoimmune diseases. It may also suggest an allergic reaction affecting the joint or an infection. Low or normal basophil counts are typically seen in non-inflammatory joint conditions like osteoarthritis. This test helps doctors differentiate between various types of arthritis and joint disorders to guide appropriate treatment.
Frequently asked questions
Does the test hurt?
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