thyroid function tests(tfts)

7/24/2019 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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$usected hyerthyroidism

$trategy

6T( then TS;


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$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

thyroid function tests(tfts)

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