Thyroxine (T-4)
Label Mnemonic: T4
Epic code: LAB126
Downtime form: A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery
Chemistry
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
Plasma Separator Tube 4.5 mL
Alternate Collection Media:
Call laboratory for additional acceptable specimen collection containers.
Minimum:
3 mL whole blood in light green top or TWO Microtainer® devices.
Testing Schedule:
24 hrs/day, 7 days a week, including holidays.
Turn Around Time:
1 hour (upon receipt in laboratory)
Reference Range:
         AGE          MALES/FEMALES
      0 - 3 days     8.0-20.0 μg/dL
      3 - 30 days    5.0-15.0 μg/dL
31 days - 1 years    6.0-14.0 μg/dL
      1 - 5 years    4.5-11.0 μg/dL
      6 - 18 years   4.5-10.0 μg/dL
  Normal adults      4.6 12.0 μg/dL
Comments:
Assay updated with increased tolerance to biotin on March 7, 2023.
Test Limitations:
The assay is unaffected by icterus (bilirubin is less than 37 
mg/dL), hemolysis (Hb is less than 2300 mg/dL), lipemia (triglycerides 
is less than 2500 mg/dL) and biotin is less than 1200 ng/mL (criterion: 
recovery within plus or minus 10% of initial value).

No interference was observed from rheumatoid factor (up to 2400 U/mL) 
and samples from dialysis patients.

In vitro tests were performed on 15 commonly used pharmaceuticals. No 
interference with the assay was found.

Autoantibodies to thyroid hormones can interfere with the assay.  The 
risk of interference from potential immunological interactions between 
test components and rare plasma has been minimized by the inclusion of 
additives.

In rare cases, interference due to extremely high titers of antibodies 
to ruthenium can occur.  T4 reagent contains additives which minimize 
these effects.

Extremely high titers of antibodies to streptavidin can occur in 
isolated cases and cause interference.

For diagnostic purposes, the T4 findings should always be assessed in 
conjunction with the patient's medical history, clinical examination 
and other findings.
Methodology:
Electrochemiluminescence Immunoassay
CPT Code:
84436
 
See Additional Information:
Biotin Interference with Immunoassays