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HelpTest Code ZFT-4 Free Thyroxine (500454)
Additional Codes
LabCorp Test Code: 500454
Synonyms/Keywords
Thyroxine, Free T4, Free T-4, Tetraiodothyronine
Specimen Requirements
| Fasting Required | Specimen Type | Preferred Container/Tube | Acceptable Container/Tube | Specimen Volume | Specimen Minimum Volume (allows for 1 repeat) |
Pediatric Minimum Volume (no repeat) |
|---|---|---|---|---|---|---|
| Serum | Serum Separator Tube (SST) | Red Top Tube (RTT) | 1 mL | 0.8 mL |
Collection/Processing Instructions
Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
Serum must be separated from cells within 45 minutes of venipuncture. Send serum in a plastic transfer tube. FREEZE.
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum |
Frozen (preferred) | 200 days |
| Refrigerated | 7 days |
|
| Ambient |
Rejection Criteria
Plasma or whole blood samples received.
Test Components
Thyroxine (T-4), Serum
Thyroxine, Free (fT4)
Test Information
Testing is performed at Esoterix Endocrinology Lab (a division of LabCorp). (Esoterix test code: ES#500314)
Note: Test is not found in LabCorp test catalog available to the public. You must be signed in under Marshfield Clinic account on LabCorp website to view this test.
Interferences
This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation.
Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
Reference Range Information
Thyroxine (T-4) (Units: ug/dL)
Age:
- Premature (26 - 30w) Day 3 - 4: 2.6 - 14.0
- Full-term Day 1 - 3: 8.2 - 19.9
- 1 week: 6.0 - 15.9
- 1 - 11m: 6.1 - 14.9
- 12m - 2y: 6.8 - 13.5
- 3 - 10y: 5.5 - 12.8
- 11 - 17y: 4.9 - 13.0
- Adults: 4.2 - 13.0
Thyroxine, Free (fT4) (Units: ng/dL)
Age:
- <4d: 0.66 - 2.71
- 4d - 1m: 0.83-3.09
- 1 - 11m: 0.48 - 2.37
- 1 - 5y: 0.85 - 1.75
- 6 - 10 y: 0.90 - 1.67
- 11 - 19y: 0.93 - 1.60
- ≥20y: 0.82 - 1.77
Performing Laboratory Name
LabCorp of America
Referral Laboratory Information
| Address | Telephone | Website Link | Marshfield Lab Account # |
|---|---|---|---|
| 6370 Wilcox Road Dublin, OH 43016-1296 |
866-235-2291 |
https://www.labcorp.com |
48300485 |
Performing Information
| Performing Location | Day(s) Test Performed | Analytical Time | Methodology/Instrumentation |
|---|---|---|---|
| LabCorp of America | Monday through Friday | 1 day | Immunoassay/ Siemens Centaur |
CPT Codes
| CPT | Modifier (if needed) |
Quantity | Description | Comments |
|---|---|---|---|---|
| 84436 |
|
Thyroxine, total |
|
|
| 84439 | Thyroxine, free |
Outreach CPT Codes
| CPT | Modifier (if needed) |
Quantity | Description | Comments |
|---|---|---|---|---|
| 84436 |
|
|
Thyroxine, total |
|
| 84439 |
|
|
Thyroxine, free |
Ordering Applications
| Ordering Application | Description |
|---|---|
| Cerner | Free T-4 (500314) |