Thyroid Clinical Application Flashcards
What is the initial screening test for suspected thyroid disorders?
TSH test
What is the most useful test for hypothyroidism?
Free T4 test
What does a total T4 test measure?
Total free T4 and TBG-T4
Which is more accurate, free T4 test or a total T4 test?
Free T4 test
What is the most useful test for hyperthyroidism?
Total T3 test
What does a total T3 test measure?
Total free T3 and TBG-T3
Which is more accurate, a free T3 test or a total T3 test?
Total T3 test
What is the common order of tests for suspected thyroid disorder?
TSH and free T4 tests ordered together
Total T3 test ordered as needed after
What are thyroid antibody tests helpful to diagnose?
Thyroid autoimmune disorders and/or cancer
What test is used as a “tumor marker” after a thyroid cancer dx and what does it assess?
Thyroglobulin test
Assesses effects of thyroid cancer treatment
What does a T3 Uptake test measure?
Binding capacity of TBG
Indirectly measures amount of plasma TBG
High rT3 is associated with?
Acute crisis or severe chronic illness
If TSH is high what disorder does that indicate?
Primary Hypothyroidism
What happens in early/less severe hypothyroidism?
Thyroid gland doesn’t release enough T3/T4
Liver/kidneys convert T4 into T3 which causes T3 values to remain normal but T4 values decrease
**This is why free T4 test is most useful
Why is a free T4 test most useful in early diagnosis of primary hypothyroidism
T3 values may be normal but T4 will be the first value to decrease as hypothyroidism develops
What are lab findings for late/progressed hypothyroidism?
T4 shortage means liver/kidneys can no longer convert T4 to T3
T3 values are now also low
If TSH is low what disorder does that indicate?
Primary hyperthyroidism
What happens in primary hyperthyroidism?
Thyroid releases too much T3/T4
Why is a total T3 test most useful in early diagnosis of primary hyperthyroidism?
Liver/kidneys is converting T4 into T3, so T4 levels remain normal but T3 levels increase
What are lab findings for late/progressed hyperthyroidism?
T3 and T4 levels are now elevated
What are S/S of hyperthyroidism?
Increased CV symptoms (HTN, tachycardia)
Elevated RR
Increased BMs
Hyperactive CNS (tremors, irritable)
Negative effect on diabetes or increased risk of diabetes
What disease can cause primary hyperthyroidism?
Grave’s Disease
What is Grave’s Disease?
Autoimmune disease that causes excess secretion of T3/T4
Immune systems releases thyroid antibodies that stimulate release of T3/T4
What is another cause of primary hyperthyroidism?
Iatrogenic
Too much synthetic thyroxine
What are TSH, Free T4, and total T3 values for primary hyperthyroidism?
Decreased TSH
Elevated or normal Free T4
Elevated Total T3
What lab finding would differentiate between Grave’s disease or iatrogenic hyperthyroidism?
If thyroid antibodies are present, it would indicate Grave’s over iatrogenic cause
What is the difference between primary and secondary hyperthyroidism?
Primary is autoimmune disorder (TSH is decreased)
Secondary is due to TSH secreting adenomas (TSH will be elevated and antibodies will not be present)
What are the TSH, free T4, and total T3 values for secondary hyperthyroidism?
Elevated TSH
Elevated free T4
Elevated total T3
What is thyroid storm?
Rare but potentially fatal form of hyperthyroidism
What is the hallmark symptom of thyroid storm?
Marked increase in body temperature
What triggers thyroid storm?
Acute event (infection, surgery, medications)
What is the most common cause of primary hypothyroidism?
Hashimoto’s disease (autoimmune disorder)
What are other causes of primary hypothyroidism?
Iodide deficiency
Thyroidectomy
Radiation damage
What is myxedema?
Very severe hypothyroidism that can be potentially fatal
Sometimes used to describe skin changes seen in hypothyroidism
What can hypothyroidism cause?
Cretinism (impaired congenital development)
Gross Dwarfism
Cognitive impairment
What are the TSH, free T4, and total T3 findings of Primary Hypothyroidism?
Elevated TSH
Decreased free T4
Decreased total T3
What lab finding would indicate Hashimoto’s over other causes of hypothyroidism?
Presence of thyroid antibodies
What is the difference between primary and secondary hypothyroidism?
Primary has elevated TSH
Secondary has decreased TSH
What causes secondary hypothyroidism?
Pituitary gland pathology/
Hypopituitarism
What are other lab findings of Secondary Hypothyroidism?
Decreased levels of other pituitary hormones
(GH, FSH, LH, ADH, ACTH, prolactin)
What causes goiter to form in Grave’s disease?
Increased thyroglobulin and T3/T4 are stored in the colloid
What causes goiter to form in Hashimoto’s disease and iodide deficiency?
Increased thyroglobulin stored in colloid
