Hashimoto’s disease, also known as chronic lymphocytic thyroiditis, is an autoimmune disorder that causes the immune system to attack and damage the thyroid gland. This leads to an underactive thyroid (hypothyroidism) as the damaged thyroid is unable to produce enough thyroid hormones. Hashimoto’s is the most common cause of hypothyroidism in the United States.
Blood tests play an important role in diagnosing Hashimoto’s disease. They can detect the presence of antibodies that are characteristic of Hashimoto’s, as well as measure thyroid hormone levels to determine if hypothyroidism is present.
Antibody Blood Tests
Two types of antibodies are commonly found in the blood of people with Hashimoto’s:
Thyroid peroxidase antibodies (TPOAb)
TPOAb, also sometimes abbreviated TPO, are antibodies that attack an enzyme called thyroid peroxidase which is important for proper thyroid hormone production.
– TPOAb are found in about 95% of people with Hashimoto’s.
– High levels of TPOAb strongly indicate that a person has Hashimoto’s thyroiditis. Normal levels are under 35 IU/ml.
– TPOAb levels may initially be normal in early stages of Hashimoto’s. Levels tend to increase over time as the disease progresses.
Thyroglobulin antibodies (TgAb)
TgAb are antibodies that attack thyroglobulin, a protein that is used by the thyroid gland to produce thyroid hormones.
– About 60-80% of people with Hashimoto’s will test positive for elevated TgAb.
– TgAb are less specific than TPOAb, meaning other thyroid conditions can also cause elevated levels.
– Normal TgAb levels are under 115 IU/ml.
Having elevated levels of both TPOAb and TgAb antibodies is even more indicative of Hashimoto’s disease. However, some people may only test positive for one type of antibody.
Other Blood Tests
In addition to checking for thyroid antibodies, other blood tests are important in diagnosing and monitoring Hashimoto’s disease:
Thyroid hormone levels
Blood tests can measure levels of the thyroid hormones T3 (triiodothyronine) and T4 (thyroxine):
– Low T3 and/or T4 levels indicate hypothyroidism. Hashimoto’s destroys enough thyroid tissue over time leading to reduced hormone production.
– When first diagnosed, some patients may have normal T3 and T4 levels, but then gradually develop hypothyroidism.
– Testing T4 alone may be sufficient initial testing. If abnormal, T3 testing can provide additional information.
Thyroid stimulating hormone (TSH)
TSH is released by the pituitary gland to stimulate thyroid hormone production.
– Elevated TSH indicates the thyroid is underactive and the pituitary is attempting to stimulate it.
– High TSH along with low thyroid hormone levels confirms a diagnosis of hypothyroidism.
– Some Hashimoto’s patients first present with a high/normal TSH but still normal T4, indicating subclinical hypothyroidism that later progresses to overt disease.
Complete blood count (CBC)
A CBC provides an overview of different cells in the blood. In Hashimoto’s, characteristic findings may include:
– Mild anemia – anemia is more common in hypothyroidism
– Elevated white blood cell and platelet counts due to chronic inflammation
When Should Blood Tests be Performed?
Blood testing for Hashimoto’s disease is recommended when symptoms of an underactive thyroid are present. These can include:
– Fatigue
– Weight gain
– Depression
– Muscle weakness
– Dry skin and hair
– Constipation
– Irregular periods
– Sensitivity to cold temperatures
Testing is also indicated for those at higher risk even without symptoms:
– Middle aged women – Hashimoto’s primarily affects women starting around age 40-60 years old
– People with a family history – Having a first-degree relative with Hashimoto’s increases your risk
– Individuals with other autoimmune disorders – There is an association with type 1 diabetes, rheumatoid arthritis, vitiligo, and celiac disease
Periodic retesting of thyroid hormone and antibody levels is useful for monitoring disease progression and guiding treatment in those with established diagnoses of Hashimoto’s hypothyroidism.
Interpreting Blood Test Results
Detecting Hashimoto’s involves piecing together information from thyroid antibody tests as well as thyroid hormone levels:
Positive thyroid antibodies + elevated TSH + low T4
This pattern clearly indicates impaired thyroid function due to Hashimoto’s autoimmune destruction of the thyroid. Treatment with thyroid hormone replacement medication (levothyroxine) is warranted.
Positive antibodies + high/high-normal TSH
Presence of antibodies signals Hashimoto’s is present even if thyroid hormones are still within the normal range. These patients have early or mild thyroid failure and require close monitoring. They may eventually need thyroid medication if TSH continues to rise or T4 decreases over time.
Negative antibodies but elevated TSH and low T4
This scenario suggests non-autoimmune primary hypothyroidism, possibly related to a prior thyroid injury from radiation, surgery, or medications. Regardless of the cause, the abnormal thyroid labs signify overt hypothyroidism requiring treatment.
Role of Blood Testing in Monitoring Hashimoto’s Treatment
Once a diagnosis of Hashimoto’s hypothyroidism is established, periodic blood tests are important to assess thyroid status and guide treatment:
– TSH, T4, and sometimes T3 levels are checked every 6-12 months once the appropriate levothyroxine dose has been determined through testing.
– The goal is maintaining TSH within the normal range, which is typically 0.5-5 mIU/L. Some doctors aim for a lower TSH target in Hashimoto’s patients (1-2 mIU/L).
– Antibody levels are generally rechecked annually. A rising trend may signal worsening autoimmune activity against the thyroid.
– An increase in TSH or decrease in T4 indicates under-replacement and necessitates an increase in levothyroxine dose. The opposite findings would warrant a dose reduction.
– More frequent monitoring is required after a dosage change to ensure the new dose is optimal.
– Ongoing blood testing accounts for changes in levothyroxine requirements and antibody levels over time.
Can Blood Tests Differentiate Hashimoto’s vs Other Thyroid Diseases?
Certain patterns in thyroid blood test results can help differentiate Hashimoto’s hypothyroidism from other potential causes:
Graves’ disease
Graves’ is an autoimmune disorder that leads to an overactive thyroid (hyperthyroidism).
– TSH is low and T3/T4 elevated, opposite of Hashimoto’s.
– Grave’s disease antibodies (TSI) distinguish it from Hashimoto’s.
Thyroid nodules/goiter
Thyroid nodules and goiter (enlarged thyroid) may or may not involve hypothyroidism.
– Nodules/goiter without Hashimoto’s will not have positive antibodies. TSH can help determine if hypothyroid.
– Nodules/goiter due to Hashimoto’s will have characteristic antibodies and TSH elevation.
Thyroiditis
Thyroiditis refers to thyroid inflammation. Different types exist:
– Postpartum thyroiditis – occurs after pregnancy and involves thyroid antibodies.
– Subacute thyroiditis – caused by a virus, no antibodies present.
– Drug-induced – certain medications can provoke thyroiditis, antibodies negative.
– Radiation thyroiditis – history of radiation exposure, antibodies absent.
Thyroid cancer
Thyroid cancer does not directly cause hypothyroidism but its treatment often does.
– No Hashimoto’s antibodies expected with thyroid cancer.
– Surgical removal and radioactive iodine ablation to treat thyroid cancer frequently cause hypothyroidism.
Can Early Blood Testing for Hashimoto’s Prevent Hypothyroidism?
Unfortunately, there is currently no way to prevent the development of hypothyroidism in Hashimoto’s disease despite early detection:
– Positive thyroid antibodies indicate an autoimmune attack on the thyroid is already underway.
– Continued destruction of the thyroid is likely even if hormone levels are still normal initially when antibodies are first discovered.
– Close monitoring with periodic blood testing can identify hypothyroidism at the earliest stage once it develops.
– Early treatment with thyroid hormone replacement helps minimize symptoms and long term complications.
– But progressive thyroid failure in Hashimoto’s cannot be prevented given our current treatment limitations.
– Research on blocking the immune system’s attack on the thyroid may eventually yield new therapies.
So blood testing primarily plays an important role in diagnosing Hashimoto’s at the earliest phase and monitoring disease progression. But patients who test positive for Hashimoto’s antibodies should understand hypothyroidism is likely inevitable and requires diligent follow up care.
Conclusion
Blood tests play a vital role in identifying and managing Hashimoto’s disease. Presence of thyroid antibodies, particularly TPOAb, is the hallmark of detecting Hashimoto’s. Elevated TSH and low thyroid hormone levels indicate impaired thyroid function requiring treatment. Ongoing monitoring through bloodwork is crucial for adjusting thyroid medication dosing as the disease progresses. While early detection does not prevent the disease, recognizing Hashimoto’s at the initial stages through prompt testing allows treatment to start before symptoms become severe. Patients and doctors partnering closely together using blood tests as a guide can optimize outcomes in Hashimoto’s disease.