ModifiedBlue Cross Blue Shield - LouisianaPolicy AHS - G2045 - Thyroid Disease Testing

Thyroid Disease Testing

Rules for coverage of laboratory testing related to thyroid function, diagnosis, monitoring, and related antibody or tumor markers for members of Blue Cross and Blue Shield of Louisiana.

Policy Summary

PayerBlue Cross Blue Shield - Louisiana

PolicyThyroid Disease Testing

Policy CodePolicy AHS - G2045 - Thyroid Disease Testing

Change TypeMaterial revisions to indications, antibody frequency, and excluded tests

Effective DateJul 1, 2025

Next Review DateN/A

Key ActionBegin evaluation with TSH as the initial test and proceed to reflex testing (fT4/fT3 or antibodies) only when clinically indicated; be prepared to document indication.

SourceLink

POLICY UPDATE CHANGES

Removed 'are undergoing evaluation for infertility' from CC1.d and revised CC1.d to require TSH testing for individuals capable of becoming pregnant who have experienced two or more pregnancy losses.

Added CC1.e.: 'TSH testing for individuals with a thyroid nodule.'

Reformatted CC4 and specified thyroid antibodies (Tg-Ab, TPOAb, TRAB, TSI) with coverage once every three years for individuals with hypothyroidism or hyperthyroidism.

Added explicit statement that TBG and TRH testing DOES NOT MEET COVERAGE CRITERIA for evaluation of cause of thyroid dysfunction.

Added CPT code 84442 to coding.

specifiedMonitoring intervals

recommendedThyroid nodule testing

q3 yrsAntibody frequency

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TBG/TRHNot covered tests

Coverage Criteria for Thyroid Disease Testing

Covered indications and monitoring

Thyroid function testing meets coverage criteria in the following specified clinical situations

Hypothyroidism indications: TSH to confirm or rule out primary hypothyroidism; fT4 as follow-up to abnormal TSH; TSH and fT4 for suspected secondary (central) hypothyroidism; monitoring for primary hypothyroidism with TSH and fT4 every 6 weeks after dosage changes and annually when stable; monitoring for secondary hypothyroidism with fT4 every 6 weeks after dosage changes and annually when stable.

See Note 1 for symptoms of hypothyroidism

Hyperthyroidism indications: TSH to confirm or rule out overt hyperthyroidism; fT4 follow-up to abnormal TSH; total T3 (TT3) or free T3 (fT3) to confirm hyperthyroidism; fT4 to distinguish overt vs subclinical hyperthyroidism; monitoring after treatment with repeat TSH and fT4 every 8 weeks and annual monitoring after first year.

See Note 2 for symptoms of hyperthyroidism

Medication and risk-based screening: Annual TSH for asymptomatic individuals prescribed drugs that can interfere with thyroid function, plus testing when dosage/medication changes or if symptoms develop; TSH testing for individuals capable of becoming pregnant who have experienced two or more pregnancy losses; one-time TSH screening for asymptomatic individuals at high risk (personal/family history of thyroid dysfunction, type 1 diabetes/autoimmune disease, thyroid/neoplasm, chronic or acute urticaria, pediatric short stature or failure-to-thrive).

Includes IRT monitoring with quarterly TSH and reflex fT4/fT3 when abnormal (see population-specific criteria)

Thyroid nodule and cancer: TSH testing for individuals with a thyroid nodule; for thyroid cancer, serum thyroglobulin and/or Tg-Ab testing for detection of tumor recurrence, post-surgical evaluation, surveillance, and maintenance for differentiated thyroid carcinomas.

If TSH is subnormal in a patient with a nodule, obtain radionuclide uptake scan to assess for hyperfunctioning nodule

Immune reconstitution and special populations: For individuals undergoing immune reconstitution therapy (eg, alemtuzumab, HAART, post-allogeneic BMT/HSCT) measure TSH every 3 months with reflex fT4 and fT3 when TSH is abnormal; monitoring frequency for hypothalamic-pituitary disease: biannually if <18 years and annually if ≥18 years; annual TSH and fT4 for primary mitochondrial disease; in pregnant/postpartum symptomatic individuals, TSH and fT4 once every 4 weeks.

See guidance for pregnancy-specific testing and monitoring

Not Medically Necessary / Not Covered Tests and Contexts

Not covered tests: Testing for thyrotropin-releasing hormone (TRH) or thyroxine-binding globulin (TBG) for evaluation of the cause of hyperthyroidism or hypothyroidism does not meet coverage criteria; testing of reverse T3, T3 uptake, and total T4 (TT4) does not meet coverage criteria; measurement of TT3 and/or fT3 for assessment of hypothyroidism does not meet coverage criteria; measurement of total or free T3 to assess levothyroxine dose in hypothyroid patients does not meet coverage criteria.

Screening not covered: Testing for thyroid dysfunction in asymptomatic, nonpregnant individuals during a general exam without abnormal findings does not meet coverage criteria.

Primary testing and action criteria

Testing and subsequent actions are guided by TSH result and clinical context:

Initial testing: Measure serum TSH as the initial test for suspected thyroid dysfunction; if TSH is normal, no further testing is generally required.TSH normal

supported by scientific background

Elevated TSH pathway: If serum TSH is high, measure free T4 to determine degree of hypothyroidism.TSH high

NICE/ATA/AACE guidance

Low TSH pathway: If serum TSH is low, measure free T4 and free T3 to determine degree of hyperthyroidism; if a thyroid nodule is present and TSH is low, obtain a radionuclide thyroid uptake scan to assess for a hyperfunctioning ('hot') nodule.TSH low

Guideline-based coverage criteria

Summary coverage-relevant criteria distilled from guideline recommendations:

Initial evaluation of suspected thyroid dysfunction: TSH measurement is the recommended initial test for nonpregnant and pregnant patients when thyroid dysfunction is suspected.

Supported by ATA, AACE, ACOG, ASCP, AAFP, ES

When to perform additional testing: Order fT4 (or TT4 with pregnancy-adjusted ranges), fT3/TT3, TRAb, or antibody testing based on specific clinical indications: pregnancy with suspected thyrotoxicosis, prior Graves disease, recurrent pregnancy loss, central hypothyroidism, symptoms suggesting hyper-/hypothyroidism, or nodules.

See ATA/ACOG/ASRM guidance for timing and indications

Pregnancy monitoring: In pregnant patients treated for hypothyroidism or hyperthyroidism, monitor TSH and appropriate thyroid hormone levels approximately every 4 weeks while adjusting therapy and apply trimester-specific reference ranges.

Includes levothyroxine dosing goals and trimester TSH targets per ACOG and ATA

Primary coverage criteria

Testing approach and indications per cited guidelines

Initial assessment

If TSH above reference: Measure free T4 in the same sample.
NICE cascade guidance.
If TSH below reference: Measure free T4 and free T3 in the same sample.
NICE cascade guidance; consider fT3 when TSH low.

Indications to test: Clinical suspicion of thyroid disease; new-onset atrial fibrillation; type 1 diabetes or other autoimmune disease; depression or unexplained anxiety; children/young people with abnormal growth or behavior.

NICE-listed indications.

Population-specific criteria

Special populations and monitoring intervals

Immune Reconstitution Therapy (IRT): Measure TSH prior to IRT; if abnormal measure fT4 and fT3 as recommended; post-IRT TSH monitoring recommended, with three-monthly testing for four years after alemtuzumab; routine TSH monitoring is not universally recommended following HAART unless dysfunction suspected.

ETA guideline recommendations.

Pregnancy and assisted reproduction: For pregnant patients with Graves' or on therapy, measure maternal fT4 and TSH every 2 weeks after treatment initiation, then every 4 weeks after target achieved; screen women seeking infertility care for thyroid dysfunction and apply trimester-specific reference ranges.

ETA/ATA recommendations for pregnancy and assisted reproduction.

Pediatric Graves' and central hypothyroidism: Measure TSH receptor antibodies for pediatric hyperthyroidism; consider combined fT4 and TSH testing and repeated measurements to confirm central hypothyroidism; monitor children per ETA/NICE frequency guidance (more frequent intervals for younger children and during treatment changes).

ETA pediatric GD and CeH recommendations.

Thyroid function testing: indications and monitoring

Selected, revised coverage criteria and monitoring intervals (summarized from CC revisions):

CC1 - Indications and monitoring for thyroid function testing: Designates TSH as the primary screening test; monitoring intervals for hypothyroidism (TSH and fT4 every 6 weeks after dose change, annually if stable) and for hyperthyroidism (TSH and fT4 repeat testing every 8 weeks); one-time TSH screening for specified high-risk groups; monitoring for hypothalamic-pituitary disease (biannually if <18y, annually if ≥18y); inclusion of individuals capable of becoming pregnant with two or more pregnancy losses for TSH testing; added TSH testing for individuals with a thyroid nodule.

Revision history 03/15/2025 and 07/01/2025

Thyroid antibody testing

Antibody testing for thyroid disease

CC4 - Thyroid antibody testing: For individuals with hypothyroidism or hyperthyroidism, testing once every three years for thyroid antibodies (Tg-Ab, TPOAb, TRAb, TSI) meets coverage criteria.once every 3 years

Reformatted and specified in revision history

Tests that do not meet coverage criteria

Not covered evaluations

Excluded tests: Testing for thyroxine-binding globulin (TBG) or thyrotropin-releasing hormone (TRH) for evaluation of cause of thyroid dysfunction does not meet coverage criteria.

TBG explicitly added as not covered; revision history notes

The policy explicitly identifies several laboratory tests and contexts that DO NOT MEET COVERAGE CRITERIA. For evaluation of the cause of hyperthyroidism or hypothyroidism, testing for thyrotropin‑releasing hormone (TRH) and thyroxine‑binding globulin (TBG) is not covered. In addition, the policy lists testing of reverse T3, T3 uptake, total T4 (TT4), total T3 (TT3), and measurement of TT3 and/or fT3 for assessment of hypothyroidism as not meeting coverage criteria. Routine measurement of total or free T3 to assess levothyroxine dose in hypothyroid patients is likewise not covered. Finally, testing for thyroid dysfunction in asymptomatic, nonpregnant individuals during a general exam without abnormal findings does not meet coverage criteria.

The United States Preventive Services Task Force (USPSTF) indicates that current evidence is insufficient to assess the balance of benefits and harms of screening for thyroid dysfunction in nonpregnant, asymptomatic adults; USPSTF also recommends against screening for thyroid cancer in asymptomatic adults. This policy aligns with that stance by limiting routine screening and favoring targeted, guideline‑based testing.

This policy does not support universal screening of asymptomatic, nonpregnant adults. Professional guidance summarized in the policy (USPSTF and ASCP) recommends against routine population screening and against routine TSH screening at annual well visits for asymptomatic adults; testing is reserved for individuals with risk factors, clinical signs/symptoms, or other guideline‑specified indications.

Routine TSH screening of asymptomatic adults at annual well visits is not recommended. The American Society for Clinical Pathology (ASCP) specifically advises starting evaluation with a TSH and avoiding blanket TSH screening in routine preventive visits unless the patient is at increased risk or demonstrates signs of dysfunction.

Tests explicitly designated as not meeting coverage criteria include TRH and TBG for evaluation of causes of thyroid dysfunction, as well as reverse T3, T3 uptake, total T4 (TT4), total T3 (TT3), and measurement of TT3 and/or fT3 for assessment of hypothyroidism. The revision history reiterates that TBG is added as not covered under any circumstances.

The policy lists specific laboratory tests that do not meet coverage criteria: thyrotropin‑releasing hormone (TRH), thyroxine‑binding globulin (TBG), reverse T3, T3 uptake, total T4 (TT4), and total or free T3 (TT3/fT3) when used for hypothyroidism assessment or routine levothyroxine dose evaluation. These items are enumerated as excluded tests in the Not Medically Necessary / Not Covered section.

Guideline reviews and utilization studies support a TSH‑first testing approach. Population and ordering‑practice data demonstrate that TSH alone is the predominant initial test and sufficient in many settings; free T4 is used as a follow‑up when TSH is abnormal. Studies and guideline statements cited in the policy note the limited added value of routine T3 testing, particularly fT3, for routine monitoring and dose adjustment in levothyroxine‑treated patients.

Providers are advised to avoid routinely ordering multiple thyroid tests concurrently for an initial evaluation without documented clinical indication. The ASCP and NICE guidance summarized in the policy recommend beginning with TSH as the initial test and proceeding to reflex or targeted testing (eg, fT4, fT3) based on the TSH result; ordering broad panels up front may be considered inconsistent with these recommendations and could be subject to review.

The policy discourages routine measurement of T3 (total or free) to titrate levothyroxine (Endocrine Society recommendation) and advises against routine thyroid ultrasound when there is no palpable abnormality. Measurement of T3 is reserved for specific indications such as confirming hyperthyroidism when TSH is suppressed and fT4 is discordant.

Reiterating excluded assays, the policy designates testing for thyroxine‑binding globulin (TBG) and thyrotropin‑releasing hormone (TRH) as not meeting coverage criteria for evaluation of the cause of hyperthyroidism or hypothyroidism.

Procedure and Billing Codes

Listed thyroid and related procedure codesCPT

80438	Thyrotropin-releasing hormone (TRH) stimulation panel; 1 hour
80439	Thyrotropin-releasing hormone (TRH) stimulation panel; 2 hour
83519	Immunoassay for analyte other than infectious agent antibody or infectious agent antigen; quantitative, by radioimmunoassay (eg, RIA)
83520	Immunoassay for analyte other than infectious agent antibody or infectious agent antigen; quantitative, not otherwise specified
84432	Thyroglobulin
84436	Thyroxine; total
84439	Thyroxine; free
84442	Thyroxine-binding globulin (TBG)
84443	Thyroid stimulating hormone (TSH)
84445	Thyroid stimulating immune globulins (TSI)

1–10 of 16

1/2

Policy coding updatesCPT

84442

Thyroxine, free (direct measurement)

Not covered testsmixedNot Covered

TBG	Thyroxine-binding globulin (test)
TRH	Thyrotropin-releasing hormone (test)

Provider Actions, Documentation, and Billing Guidance

Prior Authorization

Benefit verification and pregnancy lab requirements

Coverage and prior authorization depend on the member's benefit plan; verify eligibility and benefits before ordering. Pregnancy-related thyroid testing must be performed at laboratories that provide trimester-specific reference ranges for the assays used (particularly for fT4). If trimester-specific fT4 ranges are unavailable or results are discordant with TSH, consider total T4 instead.

Verify member benefits and prior authorization requirements before ordering tests.
For pregnant or postpartum patients, ensure the laboratory uses trimester-specific reference ranges; document the lab and assay.
If fT4 reference ranges are not available or discordant with TSH, order TT4 per guidance.

Documentation Required

Radionuclide scan and pregnancy testing guidance

Thyroid radionuclide (uptake) scans are appropriate only when a low/subnormal TSH raises suspicion for a hyperfunctioning ("hot") nodule or when determining whether a nodule is autonomous. Do NOT order uptake scans for routine evaluation without a subnormal TSH or clinical indication. For patients of childbearing potential, confirm pregnancy status prior to radionuclide imaging; avoid scans in pregnant individuals unless the clinical benefit clearly outweighs fetal risk.

Background and Rationale

Thyroid hormones produced by the thyroid gland regulate metabolic homeostasis and are essential for growth and development. Thyroid‑stimulating hormone (TSH), secreted by the anterior pituitary, regulates thyroid production of thyroxine (T4) and triiodothyronine (T3). Measurement of serum TSH is the preferred initial test for evaluating suspected thyroid dysfunction because it reflects the pituitary–thyroid axis and identifies both hypothyroid and hyperthyroid states when interpreted with clinical context and, when needed, follow‑up free hormone measurements.

Definitions and Key Concepts

TSH

DefinitionThyroid-stimulating hormone (TSH) — peptide hormone secreted by the anterior pituitary that regulates thyroid production of T4 and T3.

Primary test roleTSH is the recommended primary initial test to assess thyroid function in most clinical situations (assuming steady-state and no suspected pituitary/hypothalamic disease).

Interpretation noteNormal TSH generally obviates further testing; abnormal TSH guides reflex measurement of free T4 and/or free T3 depending on direction of abnormality.

fT4 / fT3

DefinitionsFree thyroxine (fT4) and free triiodothyronine (fT3) are the unbound, bioavailable fractions of T4 and T3 in serum.

Preferred measurefT4 (and fT3 when indicated) are preferred over total T4/T3 to reflect biologically available hormone; fT4 is generally the better single indicator of thyroid function than total T4.

Policy Summary

PayerBlue Cross Blue Shield - Louisiana

PolicyThyroid Disease Testing

Policy CodePolicy AHS - G2045 - Thyroid Disease Testing

Change TypeMaterial revisions to indications, antibody frequency, and excluded tests

Effective DateJul 1, 2025

Next Review DateN/A

Key ActionBegin evaluation with TSH as the initial test and proceed to reflex testing (fT4/fT3 or antibodies) only when clinically indicated; be prepared to document indication.

SourceLink

On This Page

supported by chunks 18 and 20

Thyroid nodule management: If uptake scan shows a 'hot' nodule, malignancy risk is extremely low and further workup may not be necessary; if 'cold', proceed with further evaluation such as fine-needle aspiration biopsy as clinically indicated.'hot' vs 'cold' scan

supported by chunk 20

Suspected pituitary/hypothalamic disease: Measure both serum TSH and free T4 when pituitary or hypothalamic dysfunction is suspected.clinical suspicion of central disease

supported by chunk 18

Autoimmune thyroid disease evaluation: Testing for thyroid autoantibodies (Tg-Ab, TPOAb, TSHR-related antibodies) is appropriate when autoimmune thyroiditis is suspected and may aid diagnosis of Hashimoto's, painless, and postpartum thyroiditis.clinical suspicion of autoimmune thyroiditis

supported by chunk 21

Pregnancy-specific testing: In pregnancy, use trimester-specific TSH and free T4 ranges when available; if trimester-specific fT4 ranges are not available and fT4 is discordant with TSH, consider total T4 for assessment; monitor TSH every 4-6 weeks while adjusting levothyroxine with goal TSH between the lower reference limit and 2.5 mU/L.pregnancy

supported by chunks 22 and 37

Screening stance: Do not perform universal population screening for thyroid dysfunction in asymptomatic, nonpregnant adults; targeted screening recommended for high-risk individuals and certain pregnant populations.

Reflects USPSTF, AAFP, ATA, ASRM positions

High-risk groups warranting early testing in pregnancy: Test TSH early in pregnancy in women with history of thyroid dysfunction, symptoms, goiter, antibody positivity, age >30, type 1 diabetes or other autoimmune disorders, prior miscarriage/preterm delivery, prior head/neck radiation or thyroid surgery, family history, morbid obesity (BMI ≥40), use of amiodarone or lithium, infertility, or residence in iodine-deficient area.

Based on ATA lists

Avoid routine screening:

Do not perform routine TSH screening in asymptomatic adults during annual well visits.

ASCP recommendation against routine screening in asymptomatic adults.

Order radionuclide thyroid scans only when TSH is subnormal and a hyperfunctioning nodule is suspected.
Confirm pregnancy status (urine or serum hCG) before any radionuclide imaging; defer imaging in pregnancy unless essential and documented.
Document rationale for scan, including TSH value and clinical findings supporting hyperfunctioning nodule evaluation.

Documentation Required

Sequential testing requirement / Initial testing triggers

Start the diagnostic evaluation with a TSH measurement. Reflex or additional testing (free T4, free T3) should be performed based on the initial TSH result and clinical context (eg, low TSH → fT4 and fT3; high TSH → fT4). Ordering broad thyroid panels or multiple thyroid tests simultaneously at the initial evaluation is not consistent with guideline recommendations and may be subject to denial.

Initial test: TSH. Proceed to fT4 (and fT3 if TSH is low) only as indicated.
Avoid ordering TSH, fT4, fT3, TT4, TT3, reverse T3, TBG, and antibody panels together for the initial screen without documentation of clinical indication.
Providers must be prepared to justify ordering panels beyond an initial TSH with clinical rationale in the record.

Denial Risk

Denial triggers for non‑covered tests or contexts

Certain tests are explicitly not covered or are considered inappropriate in most evaluation scenarios. Avoid ordering these tests unless there is a clear, documented rationale consistent with policy criteria.

Not covered: TRH stimulation testing (CPT 80438, 80439) and TBG testing (CPT 84442) for routine evaluation of thyroid dysfunction.
Not covered: reverse T3, T3 uptake, TT4, TT3, and measurement of T3/T4 uptake for routine hypothyroidism assessment.
Testing for TBG or TRH does not meet coverage criteria for evaluation of thyroid dysfunction and may be denied.

Billing Rule

Ordering multiple tests concurrently for initial evaluation

Ordering multiple thyroid tests concurrently for an initial evaluation without documented clinical indication is inconsistent with guideline recommendations and may lead to non‑supported testing determinations.

Do not order broad thyroid panels at initial presentation; begin with TSH and order additional tests based on results.
Routine TSH screening in asymptomatic adults during annual well visits is discouraged.
When monitoring LT4 dose, do not order total or free T3 for dose adjustment.
Document the clinical indication when multiple tests are ordered concurrently.

Documentation Required

Required clinical documentation and clinical indication/test selection

Providers must document clinical indications and relevant evidence in the medical record to support testing choices. Documentation should include the clinical suspicion, relevant signs/symptoms, prior test results, pregnancy status and trimester, and how the ordered tests will affect management.

Record the clinical indication (eg, new‑onset atrial fibrillation, symptoms of thyroid dysfunction, thyroid nodule) and tie ordered tests to that indication.
For pregnant patients, document pregnancy status, trimester, trimester-specific reference ranges used by the lab, monitoring intervals (eg, every 4–6 weeks when adjusting therapy), and target treatment goals.
If ordering tests beyond initial TSH (eg, antibody testing, TRAb, TSI), document the specific clinical reason (eg, suspected autoimmune disease, Graves' disease, thyroid cancer surveillance).
If ordering radionuclide imaging, document TSH value, reason for imaging, and pregnancy test result.

Step Therapy

Therapeutic sequencing in pregnancy

Therapeutic sequencing in pregnancy: follow guideline-recommended monitoring and drug selection by trimester. For hypothyroid patients, monitor TSH frequently during dosage adjustment. For hyperthyroidism, choose antithyroid medication based on trimester and monitor free T4 (and total T3 when indicated) to target pregnancy-appropriate ranges.

Pregnant individuals treated for hypothyroidism: monitor TSH every 4–6 weeks while adjusting levothyroxine to achieve trimester-appropriate targets.
Pregnant individuals with overt hyperthyroidism: treat with thioamides; choose propylthiouracil (PTU) or methimazole based on trimester and clinical factors, and monitor free T4 to the upper end of pregnancy-specific normal range.
For patients with Graves' disease, obtain TRAb at 20–24 weeks when indicated.
Document medication choices, monitoring intervals, and treatment targets in the chart.

Billing Rule

Procedure codes addressed and CPT coding update

Procedure and CPT codes referenced for clinical and billing workflows. Use the codes as a reference and verify payer-specific prior authorization requirements in system.

Covered/Referenced CPTs include: 84443 (TSH), 84439 (fT4), 84481 (fT3), 84432 (thyroglobulin), 84445 (TSI), 84436 (total T4), 84480 (TT3), 84482 (reverse T3), 86376 (microsomal antibodies), 86800 (thyroglobulin antibody).
Not covered/limited: 80438, 80439 (TRH stimulation panels) — generally not meeting coverage criteria.
CPT 84442 (TBG) was added to the coding list; TBG testing is considered not covered for routine evaluation per policy updates.

When to useMeasure fT4 when TSH is abnormal to determine degree of hypo- or hyperthyroidism; measure fT3 when TSH is low and hyperthyroidism is suspected or to confirm elevated peripheral T3.

Overt vs subclinical hyperthyroidism

Overt hyperthyroidismElevated fT4 and/or fT3 with subnormal (low) TSH.

Subclinical hyperthyroidismNormal T4 and T3 with subnormal (low) TSH.

Clinical implicationTSH often detects thyroid dysfunction earlier than hormone changes; abnormal TSH directs subsequent free hormone testing to distinguish overt versus subclinical disease.

Analytical sensitivity of TSH assays

Analytical sensitivityCurrent-generation chemiluminometric TSH assays have detection limits of approximately 0.01 mU/L.

Improvement over prior assaysThis sensitivity improves on earlier assays whose detection limits were ~0.1 mU/L, enabling earlier detection of thyrotoxic states.

Practical impactHigh analytical sensitivity allows reliable discrimination between euthyroidism and hyperthyroidism before major changes in T4/T3 occur.

Trimester-specific TSH reference ranges

ATA trimester-specific TSH rangesFirst trimester: 0.1–2.5 mIU/L; second trimester: 0.2–3.0 mIU/L; third trimester: 0.3–3.0 mIU/L.

Apply population/assay-specific rangesTrimester-specific reference ranges should be applied as defined in populations with optimal iodine intake and assay method; document ranges used in pregnancy testing.

Policy notePolicy requires use of trimester-specific normal ranges for pregnancy-related coverage and documentation (see review/revision notes).

FT4/TT4 measurement in pregnancy

Preferred methodWhen available, direct measurement of free T4 by LC/MS/MS (dialysate/ultrafiltrate) is the best method during pregnancy.

Alternate approachIf LC/MS/MS is not available, use total T4 with pregnancy-adjusted reference ranges or calculate a free thyroxine index specific to assay and trimester.

Assay cautionIndirect analog immunoassays for fT4 are affected by pregnancy and vary by manufacturer; method- and trimester-specific reference ranges are required.

Cascading testing

Stepwise approachBegin with serum TSH as the initial test; if TSH is outside the reference range, reflexively measure free T4 (if high TSH) or free T4 and free T3 (if low TSH).

Guideline basisThis cascading (TSH-first with reflex hormones in same sample) approach is recommended by NICE and other guideline bodies to avoid unnecessary initial panels.

Operational noteProviders should be prepared to justify ordering additional tests beyond initial TSH with documented clinical indications (pregnancy, symptoms, high-risk conditions).

Immune Reconstitution Therapy (IRT)

Examples of IRTImmune reconstitution settings include alemtuzumab for MS, initiation of HAART in HIV, and post-allogeneic BMT/HSCT where thyroid dysfunction risk is increased.

Baseline testingMeasure TSH prior to initiating IRT; if abnormal, obtain fT4 and fT3.

Post-therapy monitoringETA recommends TSH testing every 3 months after alemtuzumab and routine TSH monitoring post-IRT as clinically indicated (routine 3-monthly monitoring for 4 years after last alemtuzumab dose).

TSH — primary screening test and reflex testing

Screening roleTSH is the recommended primary screening test for suspected thyroid dysfunction in most contexts; if TSH is normal, further testing is generally not needed.

Reflex testing intervalsUse reflex free T4 when TSH is elevated and reflex free T4/free T3 when TSH is suppressed; in pregnancy monitor TSH every 4 weeks while adjusting therapy per guidance.

DocumentationRecord clinical indication and, for pregnancy, the trimester-specific reference ranges or method used when ordering TSH and reflex tests.

Thyroid antibodies

Included antibodiesThyroid antibodies include thyroglobulin antibody (Tg-Ab), anti-thyroid peroxidase antibody (TPOAb), thyrotropin receptor antibodies (TRAb), and thyroid-stimulating immunoglobulins (TSI).

Indications for testingAntibody testing is useful when autoimmune thyroiditis is suspected and aids diagnosis of Hashimoto's, painless, and postpartum thyroiditis and in management of Graves' disease in pregnancy.

Frequency policyFor individuals with hypothyroidism or hyperthyroidism, testing for thyroid antibodies meets coverage criteria once every three years (policy revision noted).