Thyroid tests Flashcards
Thyrotropin is testing for
TSH
thyroid diagnostic options
- US
- radioiodine uptake and scan
- fine needle aspriation biopsy
Thyrotopin = TSH is tighly regulated by serum levels of
T4 and T3: negative feedback loop
the majority of T4 is free or bound? Which is more relevant
- A small fraction circulates as free T4
- only free hormone is biologically active
T4 is converted to T3 where
- thyroid
- liver (primarily)
What is endogenous hyperthyroidism
- overproduction of thyroid hormone
which conditions falls under endogenous hyperthyroidism
- graves disease
- toxic multinodular goiter
- toxic adenoma
- thyroiditis
List the thyroid antibodies
- thyroid peroxidase antibodies (TPO)
- TSH receptor antibodies (TRAb)
- Thyroglobulin antibodies (Tg)
Thyroid peroxidase antibodies (TPO) is most sensitiev for
- autoimmune thyroid disease
- identifies 95% hashimotos
- identifies 85% of graves
TSH receptor antibodies (TRAb) and thyroid-stimulating antibody (TSAb) are present in 90% of patients with
Graves disease
Thyroglobulin antibodies indicate
- inflammation or destruction of gland
- seen in hyper- and hypothyroidism and autoimmune disorders
Radioiodine uptake and scan is used to evaluate for
- Hyperthryoidism
- graves
- toxic nodular goiter
- thyroid nodule
Radioiodine uptake and scan reflects what
iodine metabolism of gland
Radioiodine uptake and scan contraindicated in
- pregnancy
- breastfeeding
Radioiodine uptake and scan: High uptake indicates
excessive synthesis
Radioiodine uptake and scan: Low uptake indicates either
- inflammation/destruction of thyroid tissue with release of preformed hormone into circulation
- extrathyroidal source of thyroid hormone
How will graves disease and nodules/TMG differ on Radioiodine uptake and scan
- Graves: homogenous uptake
- nodules or TMG: irregular uptake
do hyperfunctioning “hot” nodules need to be biopsied?
- no
- they are rarely malignant
What values would you expect in graves disease
- TSH
- FT4
- T3
- RAI uptake/scan
- TSH low
- FT4 and T3 elevated
- RAI: homogenous, increased uptake
What is the most common cause of primary hypothyroidism
hashimoto thyroiditis
Central hypothyroidism can be either secondary or tertiary. where is the problem
- secondary: pituitary
- tertiary: hypothalamus
in central hypothyroidism, what do you expect TSH, T4 and T3 levels to be
ALL LOW
iatrogenic hypothyroidism is caused by
- tx with radioactive iodine
- medications
- lithium
- amiodarone
- iodinated contrast agents
risk of thyroid CA higher in
- children
- adults < 30 or > 60
- h/o head and neck irradiation
- fhx of thyroid CA
If thyroid nodules are hypofunctioning, or “cold” are they more likely to be malignant?
yes
List steps of evaluation for thyroid nodules
- order TSH
- low -> order thyroid uptake and scan
- hot nodule -> likely benign
- check FT4, if high, treat hyperthyroidism
- cold nodule -> consider FNA biopsy
- hot nodule -> likely benign
- normal or elevated
- consider FNA biopsy
- check for TPO antibodies
- if high -> hashimoto thyroiditis
- low -> order thyroid uptake and scan
TPO antibodies are elevated in what condition
Hashimoto thyroiditis
What percentage of hot and cold nodules are benign
- hot nodule: almost always benign
- cold nodule: 90-95% benign; 5-10% malignant
What is the most sensitive test for evaluating thyroid nodules
thyroid US
What is the single most accurate, reliable, cost effective test to diagnose thyroid CA
fine needle aspiration biopsy (FNA)
