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Blast Cells, Synovial Fluid — Cell Count

Published: August 9, 2026Updated: August 17, 2026

Examines joint fluid for blast cells, which are immature white blood cells that may indicate a blood disorder affecting the joint.

Quick summary

["Detecting blast cells in joint fluid may prompt evaluation for leukemia or another blood-cell disorder."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
33412-8
Short code
Blasts NFr Pcar
Synonyms
Blasts NFr Pcar
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What is this test?

This test examines synovial fluid, the lubricating fluid inside a joint, for blast cells. Blast cells are immature white blood cells that normally are found mainly in the bone marrow.

Why might I need this test?

It may be ordered when joint swelling or fluid accumulation is unexplained, especially if other findings suggest a blood disorder. Detecting blast cells in joint fluid can be an important clue to leukemia or another abnormality involving blood-cell production.

How is the test performed?

A clinician removes a small amount of joint fluid with a needle. A laboratory examines the fluid, using microscopy and sometimes flow cytometry, to identify and count blast cells.

How do I prepare for the test?

Follow your clinician's instructions for joint-fluid aspiration. Fasting is usually not required specifically for this test, but tell the clinician if you have a bleeding disorder, take blood thinners, or have an infection at the injection site.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Synovial fluid blast cell count

Frequently asked questions

Are blast cells always a sign of cancer?
No. Blast cells are not normally expected in joint fluid, so their presence can be important, but the result must be interpreted with other laboratory findings and your clinical history.
Is this the same as a routine joint-fluid cell count?
It is a specialized part of joint-fluid analysis that specifically looks for immature white blood cells. It may be performed alongside other tests on the same sample.
What happens if blast cells are detected?
Your clinician may recommend additional blood tests, bone-marrow examination, or urgent evaluation by a hematologist. The urgency depends on your symptoms and the overall laboratory findings.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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 17, 2026. · Read our editorial policy