Labs: Thyroid Disorders Flashcards
A patient with apparent symptoms of hypothyroidism. What laboratory tests would be the most appropriate to perform?
TSH: usually measured first because if it’s normal, then the problem is likely not in the thyroid. Neg feedback should alter TSH levels. If TSH abnormal, check T3/T4
TSH ↑ with T3/T4 ↓: primary hypothyroidism. Now check antibodies for Hashimoto’s (anti-TPO, but not specific to Hash) and Grave’s (anti-TSH)
TSH ↓ and T3/T4 ↓: secondary hypothyroidism: pituitary not releasing enough TRH. Try TRH stimulatory test. [note rare possibility of hypothalamic/tertiary problem]
A 40 year old woman seeks evaluation for subfebrility and diarrhea commenced 2–3 weeks before. Blood glucose: 6.6 mmol/l. Blood pressure: 160/85 mmHg, heart rate: 120/min. Serum TSH: 0.15 mU/l (decreased), FT4: 60 pmol/l (elevated), TRAb titer elevated, TPO-antibody positive. What is the most likely diagnosis? What other test would you order to specify your diagnosis?
Most likely Grave’s Disease (↓ TSH, anti-TPO)
Other tests: Check for anti-TSH antibodies.
Radioactive Scintigraphy: Increased radioactive iodine uptake: see “diffuse warmth” while thyroid adenomas show some hot, some cold spots.
Maybe fine needle aspiration to see if it’s cancerous.
A 42 year old woman developed diffusely enlarged, painless thyroid glands. Total T4 is decreased, thyroid uptake of radioiodine is low. ECG reveals low voltage and bradycardia. The thyroid autoimmunity panel demonstrates the presence of TgAb and TPO-Ab. What is the most likely diagnosis? Is this condition characterized by a hypo or hyperfunction of the thyroid gland?
Probably Hashimoto’s Thyroiditis: many signs of hypothyroidism + anti-TPO and anti-Thyroglobulin.
Other hypothyroid causes that are ruled out by antibodies: iodine deficiency, subacute thyroiditis, congenital thyroid issues, neoplasms.
Other (unlikely) option is late-stage Grave’s disease where the thyroid is destroyed and hypothyroidism begins
A schoolgirl at the age of 14 without any complaints develops diffusely enlarged painless thyroid glands recognized accidentally by the school doctor. Laboratory findings: FT4 is slightly decreased, whereas total T3 is slightly elevated. Thyroid uptake of radioiodine is increased. FT4 gets normalized after treatment with inorganic iodine. What is the most likely diagnosis? Try to interpret the opposite changes in hormone levels.
Iodine Deficiency is likely cause bc of FT4 normalization after treatment with iodine.
Changes in hormone levels: T4 has 4 iodine atoms and T3 has 3, so T3 is preferentially synthesized to use iodine more efficiently.
An 11 month old baby with protruded belly and retarded in movement development has been brought for medical evaluation. Serum FT4 and FT3 are decreased. Serum MIT/DIT are elevated and their urinary excretion increased. What is the most likely diagnosis?
Cretinism, likely due to TPO deficiency (cannot make enough T4/T3, so have elevated MIT/DIT)
Use perchlorate test for diagnosis (not really sure why, may differentiate Na/I transporter problem from others)
List those thyroid tests that are considered helpful in the diagnosis of thyroid cancer!
(why this question gotta be so aggressive)
Imaging: ultrasound (nodules are fluid-filled, solid, or hollow) scintigraphy (hot vs warm vs cold nodules)
Fine needle biopsy: cytology
Labs: e.g. [Ca2+] decrease in medullary carcinoma + calcitonin can be used as a tumor marker. Other less-specific tumor markers like CEA can be used.
