TEST DIRECTORY... | MIDx Labs

- PROFILE - THYROID

The Thyroid Profile provides a complete assessment of thyroid hormone status, reporting both the free and total fractions of thyroxine and triiodothyronine alongside thyroid-stimulating hormone. TSH is the most sensitive single indicator of thyroid function in patients with an intact hypothalamic-pituitary axis, and Free T4 defines the degree of hormonal excess or deficiency. Free T3 and Total T3 characterize thyrotoxicosis, including T3-predominant disease, in which T3 rises before T4 and may be the only abnormal hormone.

Thyroid peroxidase antibody is reflexed automatically on an elevated TSH to establish autoimmune etiology. Reporting both free and total fractions permits a comparison that is useful whenever thyroxine-binding globulin concentration is altered. Pregnancy, estrogen or oral contraceptive use, nephrotic syndrome, hepatic disease, and inherited binding protein variants all shift the total fractions independently of thyroid status, and in those settings either fraction read on its own can mislead.

Intended for the evaluation of suspected hypothyroidism or hyperthyroidism, assessment of goiter or thyroid nodule, and investigation of symptoms including fatigue, weight change, heat or cold intolerance, palpitations, tremor, hair and skin change, or menstrual irregularity. Thyroid function testing should not be performed during acute non-thyroidal illness, where transient abnormalities are common and do not reflect underlying thyroid status.

LIS PROFILE CODE: (MID) Thyroid Profile

INDIVIDUAL LIS TEST/PANEL CODES INCLUDED WITHIN PROFILE: TSH, FT3, FT4, TT3, TT4, ATPO (reflexed if TSH is elevated)

CPT CODE: 84443 (TSH) + 84481 (FT3) + 84439 (FT4) + 84480 (TT3) + 84436 (TT4) + 86376 (ATPO - billed only when performed)

NOTE: This is an MID-defined profile, not an AMA-recognized panel; components are billed individually and each must be supported by documented medical necessity for the individual patient. Free and total fractions of the same hormone are frequently treated as duplicative by payers, and denial of one of each pair should be anticipated. Reflex thyroid peroxidase antibody is billed separately under 86376 only when the reflex criterion is met.

ALIASES: Complete Thyroid Panel, Full Thyroid Profile, Thyroid Function Panel, Comprehensive Thyroid Assessment

METHODOLOGIES: Chemiluminescent Microparticle Immunoassay (CMIA)

PATIENT PREPARATION: Fasting is not required. Collection should occur in the morning where possible; TSH follows a diurnal rhythm that is highest overnight and in the early morning, and serial monitoring should use a consistent collection time.

Biotin must be withheld. Patients taking high-dose biotin (>5 mg/day, including hair, skin, and nail supplements) must discontinue for a minimum of 8 - 12 hours prior to collection, and 72 hours is strongly preferred for this profile. Biotin interference on immunoassay platforms produces falsely low TSH with falsely elevated Free T4 and Free T3, a pattern indistinguishable from thyrotoxicosis that has resulted in misdiagnosis and inappropriate treatment.

SPECIMEN:

- Type: Serum

- Container: Gold Top (SST) Vacutainer

- Minimum Volume Required: 2 mL

- Storage/Handling: Allow 30 minutes for blood to clot, then centrifuge specimen at 3500 RPM for 10 minutes. Maintain specimen in the refrigerator until testing can be performed.

- Stability:

Room Temperature (20-25 °C): Not Accepted

Refrigerated (2-8 °C): 3 days

Frozen (-20 °C or colder): Not Accepted

- Turnaround Time: 24 - 48 hours from receipt.

Special Instructions: If testing will be delayed for more than 8 hours, remove serum from the separator gel and transfer into a separate plastic screw-cap transport container.

Reflex testing. Thyroid peroxidase antibody is performed automatically on any specimen with a TSH above the upper limit of the reference interval and is reported with the profile. The reflex is most informative in subclinical hypothyroidism, an elevated TSH with a normal Free T4, where antibody positivity identifies autoimmune thyroiditis and predicts progression to overt hypothyroidism. A suppressed TSH does not trigger the reflex; where Graves' disease is suspected, order TSH receptor antibody or thyroid stimulating immunoglobulin, which are diagnostic in that setting where TPO antibody is not.

Total T4 and Total T3 reflect the bound hormone pool and vary with thyroxine-binding globulin concentration independently of thyroid status. Pregnancy, estrogen and oral contraceptive use, tamoxifen, and hepatic disease raise binding protein and therefore the total fractions; androgens, glucocorticoids, and nephrotic syndrome lower them. Where free and total fractions are discordant, the free fraction generally reflects true thyroid status, with the exception of pregnancy, in which free T4 immunoassays are unreliable and trimester-specific interpretation is required. Total T3 is more reliably standardized than Free T3 and is the preferred measurement in the assessment of thyrotoxicosis.

Neither T3 measurement has a role in the evaluation of hypothyroidism or in the monitoring of levothyroxine therapy. Following a change in thyroid hormone dose, TSH requires approximately 6 weeks to reach a new steady state; earlier collection will not reflect the adjusted dose. For patients on levothyroxine, note the time of the last dose, as Free T4 peaks approximately 2 - 4 hours following ingestion, and a specimen drawn shortly after a dose may show a transiently elevated result. Thyroid function testing is not interpretable during acute non-thyroidal illness. Low T3, and in severe illness low T4 with a non-elevated TSH, are expected findings in this setting and resolve with recovery.

REJECTION REASONS: QNS, Gross Hemolysis, Gross Lipemia, Contamination, Stability Violation, Expired Container, Incorrect Container

REFERENCE RANGES:

Please refer to individual test/panel directory pages for reference ranges for each test/panel included.