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TSH w/ Reflex to Free T4
Test Code
361278
CPT Code(s)
84443
Includes
Free T4 will be performed at an additional charge (CPT code(s): 84439) when TSH result exceeds age/gender specific reference range.
Preferred Specimen(s)
1 mL serum
Minimum Volume
0.7 mL
Alternative Specimen(s)
Sodium heparin (green-top) tube
Specimen Container
Plastic screw-top vial
Specimen Stability
Serum
Room temperature: 7 days
Refrigerated: 7 days
Frozen: 28 days
Plasma
Room temperature: 72 hours
Refrigerated: 7 days
Frozen: 28 days
Methodology
Immunoassay (IA)
Performing Laboratory
| Quest Diagnostics Nichols Institute |
| 14225 Newbrook Drive |
| Chantilly, VA 20153 |
Setup Schedule
Monday-Sunday All Shifts; Report available: Next Day
Reference Range(s)
| Premature Infants (28-36 Weeks) | |
| 1st Week of Life | 0.20-27.90 mIU/L |
| Term Infants (>37 Weeks) | |
| Serum or Cord Blood | 1.00-39.00 mIU/L |
| ≤4 Days | 3.20-35.00 mIU/L |
| 5-6 Days | Not established |
| 1-4 Weeks | 1.70-9.10 mIU/L |
| 1-11 Months | 0.80-8.20 mIU/L |
| 1-19 Years | 0.50-4.30 mIU/L |
| ≥20 Years | 0.40-4.50 mIU/L |
| Pregnancy | |
| First Trimester | 0.26-2.66 mIU/L |
| Second Trimester | 0.55-2.73 mIU/L |
| Third Trimester | 0.43-2.91 mIU/L |
TSH levels decline rapidly during the first week of life in most children, but may remain transiently elevated in a few individuals despite normal free T4 levels. For proper interpretation of an abnormal TSH from a newborn thyroid screen, a free (or total) T4 is usually required.
Clinical Significance
For differential diagnosis of primary, secondary, and tertiary hypothyroidism. Also useful in screening for hyperthyroidism. This assay allows adjustment of exogenous thyroxine dosage in hypothyroid patients and in patients on suppressive thyroxine therapy for thyroid neoplasia.
Reference ranges are provided as general guidance only. To interpret test results use the reference range in the laboratory report.
(The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.)
* The tests listed by specialist are a select group of tests offered. For a complete list of Quest Diagnostics tests, please refer to our Directory of Services.