Clinical Chemistry

Thyroid function tests

elevated FT3 and T3

normal FT4


< 5% of hyperthyroid individuals –> T3 toxicosis



 Critically ill, elderly, hospitalized Patient

TSH = nml or decreased (5-9%of cases)

T3 decreased



Euthyroid sick syndrome

elevated rT3

T4 –> T3 + rT3



First line test for giagnosing hypo- / hyperthyroidism

Hyperthyroid Patient with normal/decreased RAIU



Struma ovarii / Exogenous thyroid hormone

TRH stimulation test:

Exaggerated secretion of TSH

1o hypothyroidism due to intrinsic thyroid hypofunction


TRH –>+ TSH , GH, prolactin

Testing Strategy for:


Pregnancy, neonates, inpatients wit comorbidities

Most common cause of hyperthyroidism

Graves disease >95% –> TSI/LATS Ab’s –>+Rc-TSH

~60% –> antimicrosomal Ab’s


~30%–> anti-thyroglobulin Ab’s

low TSH

normal FT4

additional test?

FT3 –> T3 thyrotoxicosis

low TSH

normal FT3 & FT4

mild/subclinical hyperthyroidism


medication effect

Most common cause of hypothyroidism

Hashimoto thyroiditis

others: lymphocytic/granulomatous thyroiditis, I-131 Rx, Radiation, Drugs(Iodine,Li,IL-2,a-IFN)

Refetoff syndrome (rare)

Anti-microsomal and anti-thyroglobulin Ab’s

–> a/w ?

Hashimoto thyroiditis


Pt with elevated TSH

normal FT4

subclinical / mild hypothyroidism

normal/low TSH

low FT4

what is the next test?

r/o anterior pituitary pathology

complete evaluation of pituitary gland

Euthyroid Pt

normal TSH

elevated total thyroxine (T3 + T4)

Increase circulating TBG


pregnancy / exogenous estrogen (OCP)

Amiodarone and thyroid effect

–> direct thyroid toxicity and [Iodine]

iodine-rich–> hypothyroidism

iodine-poor–> hyperthyroidism 



Refetoff syndrome

autosomal dominant

–> peripheral hormone resistance

Normal neonate


T4serum,FT3 , FT4

@Delivery–> neonatal hypothyroidism =>

TSH peak @ ~ 1hr post delivery*

=> peak  T4serum,FT3 , FT4 –> 24-36hrs

*preterm/sick neonates => smaller peaks/delayed TSH response

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