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Anti-microsomal antibodies
Thyroid
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No Fasting Required
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Anti-microsomal antibodies are autoantibodies that target thyroid peroxidase (TPO) — an enzyme located on thyroid microsomes essential for the synthesis of thyroid hormones (T3 and T4)
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Anti-microsomal Antibodies - Comprehensive Medical Test Guide
- Why is it done?
- Test measures autoimmune antibodies directed against thyroid peroxidase (TPO), an enzyme found in the microsomal fraction of thyroid cells
- Primarily used to diagnose autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease
- Ordered when patients present with thyroid dysfunction symptoms such as fatigue, weight changes, temperature sensitivity, or goiter
- Used to differentiate autoimmune thyroid disease from other causes of thyroid dysfunction
- May be performed in patients with elevated TSH levels or abnormal thyroid function tests
- Commonly ordered for patients with family history of autoimmune thyroid disease or other autoimmune conditions
- Used in pregnancy screening and fertility evaluation as autoimmune thyroid disease can impact conception and pregnancy outcomes
- Normal Range
- Reference ranges vary by laboratory; typical normal range is less than 0.4-1.0 IU/mL or International Units per milliliter
- Results are typically reported as either negative or positive, with quantitative measurement in IU/mL
- Negative result: Antibody levels below laboratory cutoff value; generally indicates absence of thyroid autoimmunity
- Positive result: Antibody levels at or above laboratory cutoff value; indicates presence of anti-TPO antibodies and autoimmune thyroid disease
- Borderline values: Results near the cutoff may warrant repeat testing or clinical correlation with other thyroid markers
- High positive values: Significantly elevated antibody levels may indicate more aggressive autoimmune thyroid disease
- Unit of measurement: IU/mL (International Units per milliliter); some laboratories may report as mIU/mL
- Interpretation
- Negative result: Suggests thyroid dysfunction is unlikely due to autoimmune thyroiditis; other causes such as iodine deficiency, thyroid nodules, or pituitary dysfunction should be investigated
- Positive result: Confirms presence of anti-TPO antibodies indicating autoimmune thyroid disease; supports diagnosis of Hashimoto's thyroiditis or other autoimmune thyroid conditions
- Mild elevation: May indicate early-stage autoimmune thyroid disease or subclinical thyroiditis with normal thyroid function
- High elevation: Typically indicates active autoimmune thyroid disease with significant thyroid inflammation and dysfunction; correlates with greater risk of progression to hypothyroidism
- Combined with anti-thyroid peroxidase and anti-thyroglobulin: Presence of multiple antibodies indicates more aggressive disease and greater likelihood of hypothyroidism development
- Transient positivity: May occur with viral thyroiditis or post-partum thyroiditis; repeat testing may show conversion to negative
- Factors affecting results: Medication use (lithium, interferon), iodine intake, hormonal status, pregnancy, and other autoimmune conditions can influence antibody levels
- Clinical significance: Positive results warrant thyroid function testing (TSH, free T4) to determine thyroid status and need for treatment
- Antibodies may persist even after thyroid hormone replacement therapy; persistent positivity does not necessarily indicate treatment failure
- Associated Organs
- Primary organ: Thyroid gland (endocrine gland located in the anterior neck)
- Hashimoto's thyroiditis: Most common autoimmune thyroid disease characterized by chronic thyroid inflammation leading to hypothyroidism
- Graves' disease: Autoimmune condition causing hyperthyroidism; may also have positive anti-TPO antibodies
- Post-partum thyroiditis: Autoimmune thyroid inflammation occurring in the postpartum period; can present with transient hyperthyroidism followed by hypothyroidism
- Silent thyroiditis: Autoimmune thyroid inflammation without clinical presentation; antibodies may be present
- Associated autoimmune conditions: Type 1 diabetes mellitus, systemic lupus erythematosus, rheumatoid arthritis, celiac disease, and pernicious anemia
- Thyroid complications: Progressive fibrosis, atrophy, goiter formation, and permanent hypothyroidism requiring lifelong replacement therapy
- Secondary complications: Cardiovascular effects (hypertension, atherosclerosis from hypothyroidism), metabolic disorders, reproductive issues, and depression
- Thyroid lymphoma risk: Chronic autoimmune thyroiditis increases risk of developing thyroid lymphoma, though rare
- Pregnancy complications: Increased miscarriage risk, gestational diabetes, and adverse fetal outcomes in pregnant women with positive anti-TPO antibodies
- Follow-up Tests
- TSH (Thyroid-Stimulating Hormone): Essential follow-up to assess thyroid function; abnormal levels indicate need for thyroid replacement therapy or dose adjustment
- Free T4 (Thyroxine): Measures unbound thyroid hormone; helps determine thyroid dysfunction severity and treatment requirements
- Anti-thyroglobulin antibodies: Complementary test to identify additional autoimmune thyroid markers; presence increases disease severity
- TSI (Thyroid Stimulating Immunoglobulin): Ordered if Graves' disease is suspected; positive result confirms autoimmune hyperthyroidism
- Thyroid ultrasound: May be performed to assess thyroid structure, exclude nodules, and evaluate disease progression
- Thyroid scan with uptake: Helps differentiate causes of hyperthyroidism and assess thyroid function
- Screening for other autoimmune conditions: Celiac panel, tissue transglutaminase (tTG), tissue typing (HLA), or other autoimmune serologies as indicated
- Monitoring frequency: Initial testing followed by TSH rechecking in 4-6 weeks if treatment initiated; then annually or as clinically indicated
- Pregnancy monitoring: Baseline TSH and anti-TPO testing before conception; repeat testing in first trimester and third trimester during pregnancy
- Repeat anti-TPO testing: Generally not needed routinely unless clinical course significantly changes; persistent positivity expected with chronic autoimmune disease
- Fasting Required?
- No - Fasting is not required for anti-microsomal antibody testing
- Test can be performed at any time of day without dietary restrictions
- Food and fluid intake do not affect antibody detection or result accuracy
- Medications to avoid: None specifically required to be held; however, continue thyroid replacement therapy as prescribed
- Biotin supplementation: If patient takes high-dose biotin (>2.5 mg daily), inform laboratory as it may interfere with immunoassay results; consider timing of test
- Patient preparation: Standard blood draw preparation; arrive with identification and insurance information
- Blood collection: Simple venipuncture (arm vein puncture) with serum separation tube; no special collection requirements
- Special instructions: None required; test can be combined with other routine blood work including thyroid function panel
- Timing: Test results typically available within 1-2 business days; some laboratories provide same-day results
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