Test Overview
Test Methodology

Chemiluminescent Immunoassay

Test Usage

This test promotes a cascade approach to more efficiently screen and evaluate a patient's functional thyroid status. TSH is used as the initial screening test because it provides the best indication of physiological thyroid hormone status. Increased TSH indicates inadequate levels of thyroid hormones, and a suppressed TSH indicates excess thyroid hormone activity.
No further testing will be performed if the initial TSA is within normal limits.
If the TSH concentration is >5.0 mIU/mL, a FT4 assay will be ordered to assess the likelihood and severity of potential hypothyroidism.
If the TSH is <0.3 mIU/mL, FT4 will also be automatically performed. The measurement of FT4 in the setting of low TSH allows for the more accurate assessment of potential hyperthyroidism. In cases where TSH is low and FT4 is <1.76 ng/dL, an additional FT3 assay will be performed to look for possible T3 thyrotoxicosis.

Reference Range *

See individual test (TSH, FT4 and FT3) handbook entries.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Details
Days Set Up
Daily, 24 hours
Analytic Time

4 hours

Soft Order Code
TDA
MiChart Code
TSH With Reflex to Free T4
Laboratory
Chemical Pathology
Section
Automation
Specimen Requirements
Collection Instructions

Collect specimen in a red top or SST tube. Centrifuge, aliquot serum into a plastic vial and refrigerate up to 48 hours or freeze for longer storage. Specimen may be kept at room temperature for no more than 8 hours.

Alternate Specimen
Red Top Tube
Rejection Criteria
Due to possible reflex testing of FT4 and FT3, anticoagulant samples are not acceptable.
Yellow Top Tube
Normal Volume
1.0 mL serum
Minimum Volume
0.75 mL serum
Storage Temperature
Specimen may be kept at room temperature for no more than 8 hours.
Additional Information

Test includes Thyroid Stimulating Hormone (TSH). If the TSH screen result is between 0.30 - 5.00 mU/L, no further testing is performed. If the TSH screen result is <0.3 mU/L, Free T4 (Thyroxine) (FT4) will be performed at an additional charge. If the FT4 is <1.76 ng/dL, Free T3 (Triiodothyronine) (FT3) will be performed at an additional charge. If TSH screen is >5.0 mU/L, FT4 will be performed at an additional charge. By ordering this test the clinician acknowledges that additional reflex testing will be performed and billed at a separate additional charge if indicated.

Billing
CPT Code
84443 (TSH)
Fee Code
32022 (TSH)
Reflex CPT
84439 (FT4), 84481 (FT3)
Reflex Fee Code
32008 (FT4), 32013 (FT3)
LOINC
11580-8 (TSH), 3024-7 (FT4), 3051-0 (FT3)
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