Thyroid Function Tests(TFTs)
Transcript of Thyroid Function Tests(TFTs)
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Thyroid function
tests(TFTs)
Yutapong Raruenrom
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Introductions
TFTs: a daily necessity in virtually everyfeld o medical practice
- Screening a neonate or congenital
hypothyroidism- Evaluating a patient with nonspecifccomplaints
- Evaluating a woman with inertility- Assessing a thyroid nodule
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Iodine balance- Synthesis of thyroid hormones requireiodine- Iodide is actively concentrated in thethyroid gland, salivary glands, gastric
glands, lacrimal glands, mammary glands,and choroid plexus- The total iodide content of the thyroidgland averages 75 !g, virtually all of
"hich is in the form of iodothyronines-In the steady state, 7 to # !g of iodide, ora$out %& of the total, is released from thegland daily
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Iodine balance
n average of ( !g of iodide)personingested daily in the *S+
n the steady state, virtually
e same amount, ( !g,excreted in urine+
-# !g of Iodine is uptaen
the thyroid and the sameount is excreted daily+
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Thyroid hormonesynthesis
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Thyroid hormones- T( and T in the $loodstream almost entirely
$ind to proteins
- .rotein $inding of circulating T( and T/70% $ound to thyroxine-binding
globulin(TBG)%&-%5& $ound to transthyretin 0TTR1%5&-2& $ound to al$umin& $ound to lipoproteins
- T34 is synthesied in the liver and $inds onemolecule of T( or T
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Thyroid hormones
6ree hormone- +& of total plasma T(
- +& of total plasma T
6ree T is $iologically active andmediates the eects of thyroid hormone
on peripheral tissues/ 3-4 times more otent than T4
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Dierence between T3and T4
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TFTs: Which test to order?- hoose Free hormone over Totalhormone since its results are less interered !y protein !inding
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!linical uses o" T#Ts
$creening "or thyroid disease
- 8ay use T$as an initial testIt is $oth sensitive and speci9c for $othhyperthyroidism and hypothyroidism- If a$normal continue to test #T3or #T4
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!onditions &hen T$ alone can be
misleading!ommon- Recent treatment of thyrotoxicosis- .ituitary disease
- :on-thyroidal illness
'are- TS;-secreting pituitary tumor
- Thyroid hormone resistance
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!linical uses o" T#Ts
$usected hyerthyroidism
$trategy
6T( then TS;
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!linical uses o" T#Ts
$usected hyothyroidism
- In patients "ith hypothyroid symptoms "ho
lac a history of no"n thyroid or pituitarydisease/ use T$as the initial screening "ithcon9rmation of diagnosis provided $ysu$sequent determination of the #T4 le*el
- In settings that are liely to encountercomplicated cases / testing T$+ #T3 and#T4 all together is not unreasona$le
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Interpretation of TFTs
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,o& T$ 'aised #T3 or 'aised#T4!ommon
.rimary hyerthyroidism/4raves= disease8ultinodular goitreToxic nodule
T$
#T3 or #T4
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,o& T$ 'aised #T3 or 'aised#T4'elati*ely common1
&ith lo& radioiodine uta2eTransient thyroiditis/.ostpartum.ostviral infection
0granulomatous, su$acute, >e ?uervain=s1
'are1&ith a lo& radioiodine uta2eThyroxine ingestion@ctopic thyroid tissue or struma ovarii'miodarone therapy
T$
#T3 or #T4
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,o& T$ 'aised #T3 or 'aised#T4'are1&ith a ositi*e
regnancy test4estational thyrotoxicosis "ithhyperemesis gravidarum;ydatidiform mole
6amilial gestational hyperthyroidismT$
#T3 or #T4
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,o& T$ ormal #T3 orormal #T4
!ommonSu$clinical hyperthyroidismThyroxine ingestion
'areSteroid therapy>opamine and do$utamine infusion:on-thyroidal illness
T$
#T3 or
#T4
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,o& or ormal T$ ,o& #T3 or,o& #T4
!ommon:on-thyroidal illnessRecent treatment forhyperthyroidism
0TS; remains suppressed1
'are.ituitary disease
0secondary hypothyroidism1Aongenital TS; or TR; de9ciency
T$ #T3 or#T4
T$
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'aised T$ ,o& #T3 or ,o& #T4
.rimary hyothyroidism
!ommonAhronic autoimmune thyroiditis.ost radioiodine
.ost thyroidectomy;ypothyroid phase of transient thyroiditis
T$
#T3 or #T4
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'aised T$ ,o& #T3 or ,o& #T4.rimary hyothyroidism'are (anti-T. negati*e+no '5I or surgery)
.ost @3RT to the nec
>rugs/ amiodarone, lithium,interferons, interleuin-2Iodine de9ciency4oitrogens
'myloid goitre 0large, 9rm goitre "ithsystemic amyloidosis1
T$
#T3 or #T4
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'aised T$ ,o& #T3 or ,o& #T4
.rimary hyothyroidism
!ongenital1thyroid tissue absentThyroid dysgenesis
!ongenital1thyroid tissue resentIodine transport defectsBlo" radioiodine uptae or saliva iodineIodine organi9cation defect
T$
#T3 or #T4
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'aised T$ ormal #T3 orormal #T4!ommonSu$clinical autoimmunehypothyroidism
'are;eterophile 0interfering1 anti$odyIntermittent T( therapy for hypothyroidism>rugs/ amiodarone, sertraline,
cholestyramineRecovery phase after non-thyroidal illness
T$
#T3or #T4
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'aised T$ ormal #T3 orormal #T4!ongenitalTS;-receptor defectsResistance to TS; associated "ithother 0unspeci9ed1 defects
T$
#T3or #T4
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ormal or 'aised T$ 'aised#T3 or 'aised #T4
'areIntermittent T( therapyT( overdose Resistance to thyroid hormoneTS; secreting pituitary tumour0hyperthyroid1'cute psychiatric illness 09rst %C "ees1
T$ #T3or #T4
T$
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References
olin " #ayan$ Interpretation of thyroidfunction tests.%ancet &''() *+,: (./&0
ooper1 #avid S$ Medical Management ofThyroid Disease$ &nd$ 3ew 4or5: 6norma 7ealthcare 8SA1 &''9$ (-&,$ rint
;ronen!erg1 7enry1 and