Episode Overview

Podcast: Healthier World with Quest Diagnostics
Episode: Laboratory Testing for the Diagnosis and Management of Thyroid Disorders
Date: June 5, 2024
Host: Sarah Walsh, PA, Clinical Specialist, Quest Diagnostics
Guest: Dr. Sanjay Dixit, Board-Certified Endocrinologist, Medical Director, Quest Diagnostics
Duration: 21 minutes

In this episode, Sarah Walsh and Dr. Sanjay Dixit provide a comprehensive yet accessible overview of thyroid disorders—specifically hypothyroidism and hyperthyroidism—in non-pregnant adult patients. They emphasize the critical role of laboratory testing in diagnosis and management, review clinical features, discuss testing algorithms grounded in major guidelines, and share practical insights on when and how to escalate care or refer to endocrinology. The episode aims to empower primary care and women’s health providers with evidence-based strategies and tools for navigating thyroid dysfunction in everyday practice.

Key Discussion Points and Insights

1. Prevalence and Impact of Thyroid Disorders

• Thyroid disease is common: ~12% of the US population will develop a thyroid condition; an estimated 20 million Americans are affected, with up to 60% unaware of their diagnosis.
  — [02:17] Dr. Dixit: "Women have thyroid disease more than men and older individuals have this more than younger individuals. It seems to occur most frequently in women over age 60."
• Undiagnosed hypothyroidism and hyperthyroidism carry significant risks: Including cardiovascular disease and infertility.

2. Clinical Features & Differentials

• Hypothyroidism ("yin"): Depressed mood, weight gain, cold intolerance, constipation.
  — [03:15] Dr. Dixit: "Think of it like a seesaw or the yin and the yang. Hypothyroidism: typical symptoms are a depressed mood, weight gain, cold intolerance, constipation."
• Hyperthyroidism ("yang"): Anxiety, heat intolerance, loose stools, increased appetite, tachycardia.
  — [03:15] Dr. Dixit: "Hyperthyroidism...feeling revved up all the time...Symptoms like anxiety, heat intolerance, loose stools, tachycardia, and increased appetite."
• Symptoms are nonspecific—lab testing is necessary for diagnosis.

3. Indications for Thyroid Testing

• Testing should not be universal:
  — [05:16] Dr. Dixit: "The United States Preventive Services Task Force doesn't recommend universal screening for asymptomatic adults with thyroid function tests."
• Consider testing for:
  • Individuals with strong personal/family history of thyroid disorders
  • Patients with atrial fibrillation, cardiovascular disease
  • Those with autoimmune diseases (RA, Type 1 diabetes, lupus)
  • Certain medications (amiodarone, lithium, immune checkpoint inhibitors)

4. Initial Thyroid Function Testing Strategy

• Start with TSH:
  — [06:44] Dr. Dixit: "The starting point is always going to be the TSH. It's the preferred test. It has a clinical sensitivity of 98% and a specificity of about 92%."
• Add Free T4 Immediately or Reflexively:
  • TSH with reflex to Free T4 expedites diagnosis and can improve patient satisfaction (avoids repeat blood draw).

The Diagnostic Algorithm: Test Interpretations and Next Steps

A. Elevated TSH

• Next Step: Free T4
  — [07:56] Dr. Dixit: "If the TSH is elevated, the provider would be suspecting hypothyroidism, but additional information is needed. It would be recommended to check a free T4."

• Interpretation:

  • Low Free T4: Primary hypothyroidism (thyroid gland issue)
  • Normal Free T4: Subclinical hypothyroidism; consider TPO antibody to evaluate for autoimmune causes. — [11:01] Dr. Dixit: "It may be beneficial to evaluate a specific thyroid antibody called thyroid peroxidase antibody."
  • High Free T4: Rare; suggests TSH-secreting pituitary adenoma or thyroid hormone resistance. Refer to endocrinology.

• Free T4 vs. Total T4:
  — [09:35] Dr. Dixit: "Free T4 more accurately reflects functioning of the thyroid gland compared to total T4 and it's the preferred measurement."

• Special Situations:
  If binding proteins are abnormal, measure Free T4 by equilibrium dialysis rather than immunoassay.

B. Low TSH

• Next Step: Free T4
  — [11:56] Dr. Dixit: "When a patient has a low TSH…the next step is testing that person with a free T4."

• Interpretation:

  • High Free T4: Primary hyperthyroidism
  • Low Free T4: Central or secondary hypothyroidism (pituitary issue)—refer to endocrinology
  • Normal Free T4: Order Total T3 to assess for T3 toxicosis or subclinical disease

• Further Testing in Hyperthyroidism:

  • TSI and TPO Antibodies: To diagnose Graves disease (high TSI and TPO), distinguish from other etiologies—[13:02]

• Total T3 vs. Free T3:
  — [15:08] Dr. Dixit: "Total T3 is really considered a more robust and better validated Test than free T3."

C. Special Scenarios

• Subclinical Hypothyroidism: Elevated TSH, normal Free T4. Assess TPO antibodies to guide management and predict progression.
• T3 Toxicosis: Low TSH, normal Free T4, high Total T3.
• Non-thyroid illness ("euthyroid sick syndrome"): Consider in differential for abnormal labs without classic symptoms.

The Role of Primary Care and Referral

• Primary care often facilitates early diagnosis and management by ordering tests beyond TSH if comfortable. — [16:44] Dr. Dixit: "I am an advocate for primary care providers checking additional thyroid testing to help facilitate diagnosis and to expedite referrals to endocrinologists."
• Quest's algorithm is designed for primary care to simplify the path to diagnosis and align with guideline-supported steps.

Thyroid and Cardio-metabolic Health

• Thyroid dysfunction can impact cardiovascular health: Dyslipidemia, heart failure, hypertension, atrial fibrillation. — [17:56] Dr. Dixit: "An excess or deficiency of thyroid hormone can start or even worsen cardiovascular disease. Thyroid disorders are associated with dyslipidemia, heart failure, hypertension, atrial fibrillation, et cetera."

Resources and Takeaways

Diagnostic Tools & Additional Support

• Quest provides a guideline-aligned algorithm for thyroid disorder evaluation, accessible through the podcast description and Quest's test directory under TSH, Free T4, and Total T3. — [18:37] Dr. Dixit: "Our team of medical experts have developed diagnostic algorithms that can simplify the path to diagnosis."
• Additional resources:
  • Quest Diagnostics Clinical Focus for the diagnosis and management of thyroid disorders
  • Quest Diagnostics Clinical Education Center (webinars, publications, presentations)

Final Key Takeaways

— [19:34] Dr. Dixit:

• "First, thyroid dysfunction is common. However, the symptoms are non specific, so we need objective evidence to confirm the diagnosis of hypo or hyperthyroidism, and that's where the lab testing comes in."
• "Checking a TSH along with a free T4 can facilitate diagnosis of both hypo and hyperthyroidism."
• "There are autoimmune causes for both hypo and hyperthyroidism that can be evaluated with tests such as TSI and TPO antibodies."
• "Thyroid dysfunction can cause a whole host of cardiometabolic problems such as hyperlipidemia and atrial fibrillation."

Memorable Quotes & Moments

• On the "yin and yang" of thyroid symptoms:
  [03:15] Dr. Dixit: "Hypothyroidism and hyperthyroidism, think of it like a seesaw or the yin and the yang."

• On primary care’s role:
  [16:44] Dr. Dixit: "I am an advocate for primary care providers checking additional thyroid testing to help facilitate diagnosis and to expedite referrals to endocrinologists."

• On necessity of laboratory confirmation:
  [04:29] Dr. Dixit: "The symptoms are things to take into consideration...but it's not a clinical diagnosis. Lab testing plays a large role in supporting the diagnosis of hypo or hyperthyroidism."

Timestamps for Important Segments

| Segment | Timestamp | |----------------------------------------------|:-------------:| | Episode Introduction & Theme | 00:05 | | Prevalence and Population Insights | 02:17 | | Clinical Features and Differential | 03:00–04:29 | | Indications for Testing | 04:54–06:44 | | Initial Test Selection (TSH, Free T4) | 06:44–07:41 | | Elevated TSH: Next Steps | 07:43–10:48 | | Low TSH: Next Steps | 11:41–15:21 | | Role of Antibody Testing | 11:01, 13:02 | | Primary Care & Endocrinology Interface | 16:16–17:38 | | Cardiometabolic Outcomes | 17:38–18:11 | | Quest Algorithm & Resources | 18:37–19:34 | | Summary & Key Takeaways | 19:34–20:12 |

Summary prepared for providers and learners who seek an actionable, guideline-based approach to diagnosing and managing thyroid disorders in clinical practice.