Endocrine Flashcards
1
Q
Total T4 (thyroxine)
A
- elevated in most hyperthyroid patients and decreased in hypothyroidism
- <5% of hyperthyroid patients have normal T4 but elevated T3
- T4 is highly bound, so fluctuations in serum proteins limit the value of total T4 and total T3
- Bound to prealbumin (transthyretin) and thyroid binding globulin (TBG)
2
Q
Thyroglobulin increased by ___ and decreased by ___
A
- Increased by
- pregnancy
- oral contraceptives
- estrogen therapy
- active hepatitis
- hypothyroidism
- Decreased by
- hypoproteinemic states
- androgen therapy
- cortisol
3
Q
A
4
Q
T3 resin uptake (T3RU)
A
- no longer used
- in hyperthyroidism there is high T3 resin uptake and in hypothyroidism there is low T3 resin uptake
5
Q
Free T4 and free T3
A
Correlate well with clinical thyroid status
6
Q
Euthyroid sick syndrome
A
- Reverse T3 (rT3) is a metabolic product of T4 (most of which is metabolized to T3)
- rT3 is elevated
- T3 and T4 are low
- seen in patients with nonthyroidal systemic illness
7
Q
Thyroid releasing hormone (TRH)
A
- TRH stimulation test is used in evaluation of hypothyroidism
- In primary hypothyroidism there is exaggerated secretion of TSH in response to TRH
- An inappropriate TSH response to TRH suggests hypopituitarisim
8
Q
TSH (thyrotropin)
A
- best first line test for diagnosing hypo and hyperthyroidism
- TSH elevated in hypothyroidism
- Not as helpful in hypothalamic or pituitary dysfunction and neonatal screening
- fT4 indicated in these patients in addition to TSH
9
Q
Hyperthyroidism
- diagnosis
- disease
- labs
A
- Diagnosis
- low TSH
- high serum FT4
- when FT4 is normal despite a low TSH, free T3 should be measured to assess for T3 thyrotoxicosis
- Diseases
- Graves disease is most common cause
- toxic multinodular goiter
- toxic adenoma (Plummer syndrome)
- transient hyperthyroidism in various kinds of thyroiditis
- exogenous thyroxine
- pituitary adenoma
- thyroid carcinoma
- Labs
- thyroid stimulating immunoglobulin in Graves, aka long acting thyroid stimulating antibodies
- antimicrosomal antibodies (aka, TPO antibodies found in 60% of cases of Graves
- antithyroglobulin antibodies in 30% of cases of Graves
10
Q
Hypothyroidism
- diagnosis
- causes
A
- Elevated TSH and low free T4
- Causes
- Hashimoto thyroiditis is most common cause
- Thyroidectomy
- Lymphocytic and granulomatous thyroiditis (de Quervain)
- I-131 therapy
- radiation
- drugs (iodine, lithium, IL-2, alpha-IFN)
- Hashimoto characterized by anti tissue peroxidase and antithyroglobulin (>90%) antibodies
- TSI not identified in Hashimoto
11
Q
Neonatal hypothyroidism
A
- Caused by
- Most often caused by thyroid dysgenesis
- familial thyroid dyshormonogenesis
- peripheral hormone resistance (autosomal dominant Refetoff syndrome)
- hypopituitarism
- maternal factors (maternal autoantibodies and medications)
12
Q
Nonthyroidal illness syndrome (euthyroid sick syndrome)
A
- abnormal thyroid function tests in euthyroid person suffering from a nonthyroidal illness
- decreased T3 and T4
- increased rT3
- normal TSH
13
Q
Medications that affect thyroid hormones
A
- Amiodarone causes hypothyroidism in iodine rich parts of the world and hyperthyroidism in iodine poor parts of the world
- Lithium inhibits release of thyroxine resulting in hypothyroidism
14
Q
Effect of exogenous estrogen on thyroid hormones
A
- Increase circulating thyroid binding globulin (TBG)
- thus total thyroxine (T3 and T4) are elevated
- Free thyroxine and TSH remain normal
15
Q
Characteristics of cortisol secretion
A
- Diurnal variation
- trough around midnight
- peak at 8 AM
- depends on levels of cortisol binding globulin
- low 8 AM secretion suggests adrenal insufficiency