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OKT3 Blocking Antibody Titer, Serum/Plasma — Flow Cytometry

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

Measures the level of blocking antibodies directed against OKT3, an anti-CD3 antibody used in some transplant settings.

Quick summary

["This test detects antibodies that may reduce the effectiveness of OKT3 treatment."]

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

Key facts at a glance

LOINC
35476-1
Short code
OKT3 blocking Ab Titr SerPl FC
Synonyms
OKT3 blocking Ab Titr SerPl FC
Category
thyroid
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
80
Ref high
200
Critical range
20 N/A – 400 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
CPT
84436
SNOMED
302346007
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 blood test measures the titer, or relative amount, of blocking antibodies against OKT3. OKT3 is an anti-CD3 antibody that has been used to help prevent or treat certain transplant rejection problems.

Why might I need this test?

The test may be ordered when a patient has received or is expected to receive OKT3. Detecting blocking antibodies can help the transplant team understand whether the medication may be less effective and guide treatment decisions.

How is the test performed?

A serum or plasma sample is tested using flow cytometry, a laboratory method that measures cells or cell markers with fluorescent signals. The test estimates the ability of the patient's antibodies to block OKT3.

How do I prepare for the test?

Fasting is usually not required. Because timing and prior treatments—especially recent OKT3 use—can affect the result, follow the transplant team's instructions and tell the laboratory about relevant medicines or therapies. Do not stop prescribed medicines unless your clinician tells you to.

Reference range

Adult: 80-200 ng/dLN/A

Specimen: serum

Take your thyroid medication after the blood draw if applicable. No fasting required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

OKT3 blocking antibody titer

Frequently asked questions

What is OKT3?
OKT3 is a monoclonal antibody that targets CD3, a protein on T cells. It has been used in certain transplant settings to help prevent or treat rejection.
What does a positive result mean?
A positive result means blocking antibodies against OKT3 were detected. The treating team will consider the antibody level and the overall clinical situation when deciding how to proceed.
Does this test prove that a transplant is rejecting?
No. It measures OKT3-blocking activity and cannot diagnose rejection by itself. Rejection assessment usually also requires symptoms, examination findings, and other laboratory or tissue tests.
  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