Pagana: Mosby’s Manual of Diagnostic and Laboratory Tests, 6th Edition
Case Studies
The patient, a 23-year-old woman, has had a bout of flulike symptoms over the past few weeks.
Most recently, she has become increasingly tired. She is taking birth control pills to control her
menses. Her anterior neck became painful during the past few weeks. The physical examination
results reveal that her thyroid is diffusely enlarged and mildly tender.
Studies Results
Routine laboratory tests Within normal limits (WNL)
Total thyroxine (T4), p. 442 8 mcg/dL (normal: 5–12 mcg /dL)
Free T4 0.5 ng/dL (normal: 0.8–2.7 ng/dL)
Free T4 index 0.4 ng/dL (normal: 0.8–2.4 ng/dL)
Triiodothyronine (T3), p. 449 52 ng/dL (normal: 70–205 ng/dL)
Thyroxine-binding globulin (TBG), p.
12 mg/dL (normal: 1.7–3.6 mg/dL)
Thyroid stimulating hormone (TSH),
p. 434
32 microunits/mL (normal: 2–10 microunits/mL)
Thyroid scanning, p. 780 Enlarged gland; normal shape, position, and function
of the thyroid gland. No areas of decreased or
increased uptake
Thyroid ultrasound, p. 838 Enlarged gland; normal shape and position of the
thyroid gland
Thyroid antibodies
Antithyroglobulin antibody, p. 92 1:250 (normal: titer <1:100)
Antithyroid peroxidase antibody,
p. 93
1:500 (normal: titer <1:100)
immunoglobulins, p. 437
Diagnostic Analysis
Total T4 measures protein-bound and unbound T4. Because the patient was taking birth control
pills, her TBG was elevated; therefore, her total T4 was normal. Free T4 and FT4 index tests
measure unbound T4. When the free T4 and the FT4 index were measured, they were found to be
low, indicating that the patient had hypothyroidism. The TSH level was elevated because of
primary failure of the thyroid. The thyroid antibodies were elevated, indicating that the patient
had Hashimoto thyroiditis. Her long-acting thyroid stimulator (LATS) levels were normal,
discounting Graves disease as a cause of her diffusely enlarged thyroid. Her thyroid ultrasound
and scan failed to show any localized, defined tumor.
The patient was started on thyroid replacement therapy, and her TSH level returned to normal.
Over the next few weeks, she felt markedly better. Her thyroid pain and tiredness disappeared.
Case Studies
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Critical Thinking Questions
1. Why were the thyroid antibodies important in this patient’s diagnosis?
2. What symptoms might she experience if too much thyroid replacement medication were

The thyroid antibodies were important in this patient’s diagnosis because they indicated the presence of Hashimoto’s thyroiditis. Hashimoto’s thyroiditis is an autoimmune disease where the body’s immune system attacks the thyroid gland, leading to inflammation and eventual destruction of the thyroid tissue. The elevated levels of antithyroglobulin antibody and antithyroid peroxidase antibody confirmed the presence of autoimmune thyroiditis and helped differentiate it from other causes of hypothyroidism. These antibodies are commonly seen in Hashimoto’s thyroiditis and can help in confirming the diagnosis.

If too much thyroid replacement medication (thyroid hormone) were administered to this patient, she might experience symptoms of hyperthyroidism. Hyperthyroidism occurs when there is an excessive amount of thyroid hormone in the body. Symptoms of hyperthyroidism may include:

Increased heart rate or palpitations
Weight loss or difficulty gaining weight
Nervousness, anxiety, or irritability
Tremors or shaky hands
Heat intolerance or increased sweating
Increased appetite
Changes in menstrual patterns
Fatigue or muscle weakness
Sleep disturbances
It is important to closely monitor thyroid hormone levels and adjust the dosage as needed to avoid overtreatment or undertreatment, as both can lead to undesirable symptoms and complications. Regular follow-up and thyroid function tests are necessary to ensure the optimal balance of thyroid hormone replacement.

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