What is a full lab workup for a patient with an established diagnosis of Hashimoto's (Autoimmune Thyroiditis) disease?

Laboratory Workup for Established Hashimoto's Thyroiditis

For patients with established Hashimoto's thyroiditis, monitor TSH and free T4 every 6-12 months once stable on treatment, or every 6-8 weeks during dose adjustments, with additional testing for complications and associated autoimmune conditions as clinically indicated. 1

Core Thyroid Monitoring Tests

Primary Tests (Required)

• TSH (Thyroid-Stimulating Hormone): The most sensitive test for monitoring thyroid function with sensitivity above 98% and specificity greater than 92%, serving as the primary marker for assessing treatment adequacy 1
• Free T4 (Free Thyroxine): Essential for distinguishing between subclinical and overt hypothyroidism, and helps interpret ongoing abnormal TSH levels during therapy as TSH may take longer to normalize 1

Monitoring Frequency

• During dose titration: Check TSH and free T4 every 6-8 weeks after any levothyroxine dose adjustment until TSH reaches target range of 0.5-4.5 mIU/L 1
• Once stable: Repeat testing every 6-12 months or sooner if symptoms change 1
• Special circumstances: More frequent monitoring (every 2 weeks) may be warranted for patients with atrial fibrillation, cardiac disease, or other serious medical conditions 1

Antibody Testing (Selective Use)

Anti-TPO Antibodies (Thyroid Peroxidase Antibodies)

• Initial diagnosis confirmation: Positive anti-TPO antibodies confirm autoimmune etiology and predict higher progression risk to overt hypothyroidism (4.3% per year vs 2.6% in antibody-negative individuals) 1
• Not routinely repeated: Once Hashimoto's is established, serial antibody monitoring provides no additional clinical benefit for treatment decisions 2, 3

Anti-Thyroglobulin Antibodies (TgAb)

• Consider in symptomatic patients: Elevated TgAb levels correlate with symptom burden including fragile hair, face edema, eye edema, and harsh voice in Hashimoto's patients 4
• Screening recommendation: Consider TgAb testing in Hashimoto's patients with significant symptom burden despite adequate TSH control 4

Screening for Associated Conditions

Vitamin B12

• Annual screening recommended: Patients with autoimmune thyroid disease should be screened periodically for vitamin B12 deficiency due to increased risk of pernicious anemia and other autoimmune conditions 1

Lipid Profile

• Baseline and periodic monitoring: Subclinical hypothyroidism affects cholesterol levels, and treatment may improve lipid profiles 1
• Frequency: Check at baseline and reassess after achieving stable thyroid hormone replacement 1

Complete Blood Count (CBC)

• Screen for anemia: Hypothyroidism can cause anemia, and autoimmune thyroid disease increases risk of other autoimmune hematologic conditions 5

Comprehensive Metabolic Panel

• Electrolytes and renal function: Include serum electrolytes (calcium and magnesium), blood urea nitrogen, and serum creatinine 5
• Liver function tests: Hypothyroidism can affect liver enzymes 5
• Fasting glucose/HgbA1c: Screen for diabetes, particularly in patients with metabolic syndrome or obesity 5

Additional Screening Based on Clinical Context

Celiac Disease Screening

• Consider in symptomatic patients: Hashimoto's thyroiditis has increased association with celiac disease 1
• Tests: Tissue transglutaminase antibodies (tTG-IgA) with total IgA level

Adrenal Function

• Screen if suspected central hypothyroidism or unexplained symptoms: Morning cortisol and ACTH if hypotension, hyponatremia, hyperpigmentation, or hypoglycemia present 1
• Critical safety consideration: Always rule out adrenal insufficiency before initiating or increasing levothyroxine, as thyroid hormone can precipitate life-threatening adrenal crisis 1

Bone Density Assessment

• Postmenopausal women with history of TSH suppression: Consider DEXA scan if patient has been overtreated (TSH <0.1 mIU/L) for prolonged periods 1
• Ensure adequate intake: Patients should maintain calcium (1200 mg/day) and vitamin D (1000 units/day) intake 1

Tests NOT Routinely Indicated

Free T3

• Not recommended for routine monitoring: Free T3 does not add information to interpretation of thyroid hormone levels in patients with hypothyroidism on levothyroxine replacement therapy 1
• Exception: Only measure when assessing for endogenous hyperthyroidism or thyrotoxicosis 1

Thyroid Ultrasound

• No role in routine monitoring: Imaging for thyroid morphology does not help differentiate among causes of hypothyroidism or guide treatment decisions in established Hashimoto's 5
• Consider only if: New palpable nodules develop, significant thyroid enlargement causing compressive symptoms, or concern for malignancy 3

Radioiodine Uptake and Scan

• No role in established hypothyroidism: All causes of hypothyroidism will have decreased radioiodine uptake, making this test non-contributory 5

Common Pitfalls to Avoid

• Over-testing antibodies: Do not repeatedly measure anti-TPO or anti-thyroglobulin antibodies once diagnosis is established, as levels do not correlate with treatment needs 2, 3
• Checking TSH too frequently: Avoid rechecking TSH before 6-8 weeks after dose changes, as this leads to inappropriate adjustments before steady state is reached 1
• Ignoring symptoms with normal TSH: Consider TgAb testing in patients with persistent symptoms despite normalized TSH, as antibody levels correlate with symptom burden 4
• Missing associated autoimmune conditions: Screen for vitamin B12 deficiency, celiac disease, and adrenal insufficiency in symptomatic patients 1
• Failing to monitor for overtreatment: Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, and cardiac complications 1

Special Population Considerations

Pregnancy or Planning Pregnancy

• Increase monitoring frequency: Check TSH and free T4 every 4 weeks until stable, then at minimum once per trimester 1
• Target TSH <2.5 mIU/L in first trimester: More aggressive normalization warranted due to fetal neurodevelopment requirements 1
• Anticipate dose increase: Levothyroxine requirements typically increase 25-50% during pregnancy 1

Patients on Immune Checkpoint Inhibitors

• Enhanced surveillance: Monitor TSH (with optional free T4) every 4-6 weeks for first 3 months, then every second cycle thereafter 1
• Lower threshold for treatment: Consider treatment even for subclinical hypothyroidism if fatigue or other symptoms present 1

Elderly Patients (>70 years)

• Age-adjusted interpretation: Normal TSH reference range shifts upward with age, with upper limit reaching 7.5 mIU/L in patients over 80 1
• More conservative targets: Slightly higher TSH targets (up to 5-6 mIU/L) may be acceptable in very elderly patients to avoid overtreatment risks 1