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HelpTest Code LAB126 T4 (Thyroxine), Total, Plasma or Serum
Reporting Title
Thyroxine/T4
Methodology
Roche Diagnostics, Electrochemiluminescence Immunoassay- RMH, MGH and GMH, MH
Performing Laboratory
OhioHealth Laboratory Services-RMH, MGH, GMH, MH Core Laboratories
Specimen Requirements
Collection Instructions:
1. Serum and Plasma gel tubes should be centrifuged within 2 hours of collection.
2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.
Submit only 1 of the following specimens:
Preferred:
Serum
Draw blood in a gold-top serum gel tube(s). Spin down and send 1 mL of serum refrigerated.
Note:
1. A speckled-top serum gel tube (s) or a plain, red-top tube(s) is also acceptable.
2. Heterophile antibodies may interfere with this assay.
3. Indicate serum on request form.
4. Label specimen appropriately (serum).
Alternate: Preferred by Siemens Users
Plasma
Draw blood in a mint green-top (heparin) gel tube(s). Spin down and send 1 mL of heparinized plasma refrigerated.
Note: 1. Heterophile antibodies may interfere with this assay.
2. Indicate plasma on request form.
3. Label specimen appropriately (plasma).
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum or plasma | Refrigerated | 8 days |
| Ambient | 4 days | |
| Frozen | 12 months |
Specimen Transport Temperature
Refrigerate/Frozen OK/Ambient OK
Reference Values
0-1 month: 9.0-23.0 mcg/dL
2-4 months: 7.5-16.5 mcg/dL
5-1 year: 5.5-14.5 mcg/dL
2-6 years: 5.5-13.5 mcg/dL
7-10 years: 5.0-12.5 mcg/dL
>11 years: 4.5-12.0 mcg/dL
T4 levels are affected by a wide variety of conditions which affect the levels of thyroid-binding proteins. Diphenylhydantoin, large doses of salicylates, and liothyronine may cause low T4 levels due to competition for binding sites on thyroid-binding globulin (not reflective of thyroid status).
Note: Severe non-thyroidal disease may lower T4.
Day(s) Test Set Up
Monday through Sunday; Continuously
Test Classification and CPT Coding
84436