UW Hospital and Clinics Lab Test Directory
| Test Name: |
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TSH Reflex Free T4
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| Test Code(s): |
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TSHT4
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| CPT Code(s): |
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84443, 84439
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| Test Description: |
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Test Component: TSH
Free T4 will be performed if the TSH is <0.36 uIU/mL or >4.20 uIU/mL.
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| Methodology: |
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Chemiluminescent Immunoassay
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| Days Performed: |
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Daily, 24 hours.
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| Turnaround Time: |
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Stat: 1 hour.
Routine: 4 hours.
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Specimen Requirements
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| Specimen: |
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Blood
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| Collection Container: |
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Preferred: Green cap with yellow ring (PST)
Also Acceptable:
Green top,
Red cap with yellow ring (SST),
Red top
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| Collection Volume: |
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Preferred: 1 mL
Pediatrics: 0.5 mL
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| Sample Analyzed: |
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Plasma or serum
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| Volume Required: |
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Preferred: 0.5 mL
Pediatrics: 0.2 mL
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| Specimen Processing: |
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Centrifuge. If a complete barrier has not formed, transfer cell-free plasma/serum to plastic vial. Refrigerate.
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| Specimen Transport: |
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Transport specimen to UWHC Core Laboratory (B4/220). Transport with coolant pack if coming from outreach location.
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| Stability: |
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Refrigerated: 7 days
Frozen: Okay
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Interpretation
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Reference Interval:
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TSH:
Age 8 days and up: 0.36 - 4.20 uIU/mL
FT4 (if performed):
1 year and up: 0.70-1.45 ng/dL
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| Test Limitations: |
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FT4:
Results may be affected if patient has developed Human Anti-Murine Antibodies (HAMA) due to exposure to murine based products.
Thyroid autoantibodies in human serum may interfere and cause falsely elevated Free T4 results.
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Thyroid Stimulating Hormone
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