Endocrine disorders 2 Flashcards
T3 and T4 bind to what proteins (2)
Most of the plasma T4 and T3 is protein bound, mainly (70 per cent) to an a-globulin, thyroxine-binding globulin (TBG), and, to a lesser extent (15 per cent), transthyretin (previously called pre-albumin)
The conversion of T4 to T3 may be reduced by (3) :
- systemic illness
- prolonged fasting
- drugs sucsh as beta blockers
The conversion of T4 to T3 may be increased by (1)
drugs that induce hepatic enzymes
What metabolic processes are affected by thyroid hormones? (5)
- They bind to specific receptors in cell nuclei and change the expression of certain genes.
- Thyroid hormones are essential for normal growth,
- Mental development
- Sexual maturation
- Increase the sensitivity of the cardiovascular and central nervous systems to catecholamines, thereby influencing cardiac output and heart rate.
Is thyroid gland more sensitive to T3 or T4?
T4
Laboratory changes in hypothyroidism
- plasma cholesterol concentration moderatly high (clearance of LDL impaired)
- plasma creatine kinase activity (due to myopathy)
- hyponatremia
- hyperprolactinemia
- reduced sex hormone binding globulin
- macrocytic anemia, raised MCV
- reduced eGFR (impaired renal perfusion)
- high TSH (in primary hypoth) or low TSH (secondary hypoth)
What is subclinical hypothyroidism?
Subclinical (compensated hypothyroidism) is the state in which plasma TSH concentration is raised but the total or fT4 concentration still falls within the reference range.
What lab tests would you order to investigate suspected hypothyroidism?
plasma TSH and total T4 or fT4
anti-TPO
Clinical signs of hyperthyroidism (7)
- heat intolerance
- fine tremor
- tachycardia + atrial fib
- weight loss
- tiredness
- sweating
- diarrhea
Lab findings in hyperthyroidism/thyrotoxicosis (5)
- hypercalcemia (increased turnover of bone cells)
- hypocholesterolamie (increased LDL clearance)
- hypokalemia
- increased plasma SHBG
- increased creatine kinase (incr. thyrotoxic myopathy)
Lab findings in hyperthyroidism/thyrotoxicosis (5)
- hypercalcemia (increased turnover of bone cells)
- hypocholesterolamie (increased LDL clearance)
- hypokalemia
- increased plasma SHBG
- increased creatine kinase (incr. thyrotoxic myopathy)
What is Graves disease?
Graves’ disease is an autoimmune thyroid disease characterized by a variety of circulating antibodies, including anti-TPO, as well as being associated with other autoimmune diseases such as type 1 diabetes mellitus, adrenal insufficiency and pernicious anaemia.
What do we consider if TSH is normal and fT4 is low? (2)
consider
1. sick euthyroid/ non-thyroidal illness,
2. certain drugs, such as carbamazepine or phenytoin.
What do we consider if both TSH and fT4 are normal? (1)
thyroid function is likely to be normal
What do we consider if TSH is normal and fT4 is high? (2)
consider
1. euthyroid hyperthyroxinaemia, 2. interfering assay autoantibodies.
What do we consider if both TSH and fT4 are low? (3)
consider
1. sick euthyroid/non-thyroid illness,
2. pituitary or hypothalamic disease (secondary hypothyroidism?),
3. certain drugs.
What do we consider if TSH is low and fT4 is normal? (3)
consider
1. sick euthyroid/non-thyroid illness,
2. subclinical hyperthyroidism, particularly if clinically hyperthyroid,
3. certain drugs, such as glucocorticoids and dopamine that may affect TSH, fT3 toxicosis (fT3 concentration is raised).
What do we consider if TSH is low and fT4 is high? (6)
consider 1. hyperthyroidism,
2. drugs such as amiodarone,
3. iodine excess, 4. hyperemesis gravidarum,
5. pregnancy,
6. activating TSH receptor mutations.
What do we consider if TSH is high and fT4 is low? (1)
primary hypothyroidism
What do we consider if TSH is high and fT4 is normal? (4)
- compensated hypothyroidism,
- inadequate thyroid replacement for hypothyroidism,
- drugs such as metoclopramide or domperidone, or
- sick euthyroid
What do we consider if both TSH and fT4 are high? (3)
- generalized thyroid hormone resistance, 2. TSH secreting tumour, 3. interfering assay autoantibodies
