Thryoid Function Tests Flashcards
Name 9 indications for TFTs
• Symptomatic patient, features of thyroid disorder, elderly and menopausal woman with nonspecific symptoms,
• family history
• taking thyroxine
Patients at risk of developing thyroid disease:
• diabetes: type 1 annually, type 2 at diagnosis
• autoimmune disease (annual)
• treated hyperthyroidism (annual)
• downs and turner’s syndrome (annual)
• post neck irradiation (annual)
• lithium or amiodarone (before treat and 6 monthly)
Name 3 types thyroid hormone
• Thyroxine T4 (produced by thyroid)
• tri-iodo thyronine T3 (biologically active,formed in liver kidneys muscle from T4 )
• reverse T3 (rt3)
Which proteins binds thyroid hormones (3)
. Thyroxine binding globulin TBG = major binding protein
• transthyretin / thyroxine binding prealbumin
• albumin
99,8% bound. 0,05% free T4, 0,2% free T3
How does amiodarone affect thyroid function
(4)
• Decrease thyroid hormone secretion
. Induce hyperthyroidism
. Impaired T3 and T4 conversion
• modified thyroid hormone action
How does lithium affect thyroid function (3)
• Decrease thyroid hormone secretion
• induce hyperthyroidism
• decrease in thyroidal synthesis
How does iodine affect thyroid function (2)
• Decrease thyroid hormone secretion
• induce hyperthyroidism
Name 10 causes low tsh
High free T4:
• overt hyperthyroidism
Normal T4
• subclinical hyperthyroidism !
• T3 hyperthyroidism (T3 toxicosis - do thyroid isotope scan)!
• non-thyroidal illness!
• treated hyperthyroid patients first 6 months
• ophthalmic Graves’ disease
• pregnancy first 20 weeks
• treatment with dopaminergic drugs or high dose glucocorticoids
Low T4
• non thyroidal illness
• hypopituitarism uncommon
Name 5 causes normal tsh with thyroid derangements
High free T4
• tsh oma (rare)
• assay interference
• thyroid hormone resistance (uncommon)
Low T4
• northyroïdal illness
• hypopituitarism (un common)
Name 7 causes high tsh
High free T4
• tsh Oma (rare)
• assay interference
• thyroid hormone resistance (uncommon)
Normal T4
• subclinical hypothyroidism
• recovery from nonthyroidal illness
Low T4
. Overt hypothyroid
• recovery from nonthyroidal illness
Name 2 signs hyperthyroid
• Exophthalmos
• goiter
Name 4 signs hypOthyroid
• Hair dry, coarse, sparse
• lateral eyebrows thin
• periobital edema
• puffy dull face with dry skin
When is tsh only ideal as a first line test
• Monitor on thyroxine
• screen at risk patients that are asymptomatic
When is tsh only not ideal as a first line test (5)
• Symptomatic patient on first presentation
• optimising treatment
• screening and monitorin in pregnancy
• diagnose and monitor hypopituitarism
• diagnose tsh Oma and thyroid hormone resistance (rane)
Approach to hypothyroidism with tsh 4,5 -10 and FT 4 normal (5)
• Exclude recovery from illness and drug causes
• repeat at 3 months to exclude transient rise in tsh (subclinical hypothyroid )
-if still no increase, do not treat with T4 unless Goitre, pregnancy
-If > 10, treat.
• request anti-tpo antibodies → positive → treat
Approach to hypothyroidism with tsh > 10 and FT 4 normal (4)
• Confirm subclinical hypothyroidism by repeat in 3 months.
• start on T4 if still >10
• retest after 8 weeks of treatment and change as needed
• when stable, annual check with tsh
Approach to hypothyroidism with tsh > 10 and FT 4 <9
Overt hypothyroid = treat with T4
Name 10 causes hypothyroid
Congenital
• thyroid aplasia
• dyshormogenesis
Acquired primary
• Iatrogenic
• inflammatory:
- autoimmune: hashimoto, atrophic thyroiditis
- transient: viral thyroiditis, postpartum thyroiditis
Acquired secondary
• hypopituitarism
• hypothalamic dysfunction
. Iodine deficiency
Name 7 causes hyperthyroid
. Inflammatory
- Graves’ disease (autoimmune, tsh receptor stimulating antibodies)
-Thyroïdites (sudden release T4) eg de Quervain thyroiditis (usually TRANSIENT with infection, resolve when remove infection)
• toxic multinodular goitre, solitary toxic nodule
• iodine induced (chronic high iodine intake or amiodarone which contains iodine)
• tsh Oma
• factitions (hypothyroid treatment)
. Trophoblastic (hcg identical to tsh so can stimulate thyroid)
Treatment and monitoring hyperthyroid?
• Radioiodine
• carbimazole
• thyroïdectomy
Can only measure tsh again after 4-6 months
Approach to tsh 0,01 - 0,2 and normal FT4 and T3? (2)
• Rule out northyroidal illness, dopamine agonists, high dose glucocorticoids
• Repeat at 6 months to see if it’s subclinical hypothyroidism → still low → treat
Approach to tsh < 0,01 and normal FT4 and T3? (2)
• Rule out northyroïdal illness, dopamine agonists, high dose glucocorticoids
• repeat in 1-2 months to see if sub clinical hyperthyroid → still low → refer
Approach to tsh < 0,01 and raised FT4 and or T3?
Overt hyperthyroidism
Refer for treatment
Name 8 lab test changes in hyperthyroid
• Hyperglycaemia /impaired glucose tolerance
• hypocholesterol
. Abnormal LFTs
• hyperca
• increase shbg
- Decrease sodium Na
- increase prolactin
- increase ck
Name 4 cases in which TFTs may be unreliable
• Northyroidal illness/sick euthyroid syndrome (usually low T3, low tsh 2x more likely due to NTI than hyperthyroid and usually > 0,01, )
• illness recovery ( usually rise tsh, more likely than hypothyroid )
• neonate (initial surge tsh, then marked decline )
•Pregnancy
Name 4 other tests that can be done for thyroid disease
• Thyroid cancer: follicular carcinoma (thyroglobulin tumour marker)
• TRH test: secondary hyperthyroid due to tsh Oma or thyroid hormone resistance
• anti thyroid peroxidase antibodies
• tsh receptor antibodies TRABs
Name 4 causes of abnormal TFT in euthyroidism
• Abnormal TBG
• genetic variants albumin and pre-albumin: familial dysalbuminaemic hyperthyroxinaemia
• assay interference: patients with endogenous antibodies that interfere with the assays
T3 vs T4
T3: active
T4: inactive, transformed to T3 (used to measure)
Name 7 causes high T4 (hyperthyroid)
Low TSH
- overt hyperthyroïd
Normal TSH: uncommon
- TSHoma
- assay interference
- thyroid hormone resistance
High TSH: uncommon
- same as above
Name 5 causes normal T4 with abnormal TSH
Low TSH
- subclinical hyperthyroidism
- T3 hyperthyroidism
- Nonthyroïdal illness!
Normal TSH = euthyroid
High TSH
- subclinical hypothyroidism
- recovery from non thyroidal illness
Name 6 causes low T4 (hypothyroid)
Low TSH
- non thyroïdal illness
- hypopituitarism (uncommon)
Normal TSH
- non thyroïdal illness
- hypopituitarism
High TSH
- overt hypothyroid
- Recovery from non thyroïdal illness
