1. ENDOCRiNE FUNCTION TESTS
MA. LOURDES TILBE, D,F,PSP

2. Objectives Review hormone regulation in health and disease
Types of endocrine testing
Basic principles behind test
Considerations in patient preparation and specimen handling
Interpretion of tests applying acquired knowledge

3. Endocrine System
Composed of different glands that secrete hormones directly in the blood
Some hormones are regulatory in nature
Trophic hormones, releasing hormones

4. Feed back External stimuli HYPOTHALAMUS PITUITARY GLAND EFFECTOR ORGAN
Synthesis and secretion of each hormone is under continous feedback control in normal physiologic conditions
External stimuli
HYPOTHALAMUS
Feed back
Releasing hormones
PITUITARY GLAND
Trophic hormones
EFFECTOR ORGAN

5. Diagnosis of Endocrine Disorders
Normally, hormone concentration in circulation falls within a predictable range
Most hormones are conveniently measured by RIA or other immunoassays.

6. Direct measurement of individual hormones in plasma or serum allows for screening and establishing diagnosis of most endocrine disorders.
Determine hyperfunction or hypofunction
Localize the diseased organ
Effector organ (primary)
Pituitary Gland (secondary)
Hypothalamus (tertiary)

7. Endocrine disorders
1o excess high target organ hormones; low trophic hormone
1o deficiencylow target organ hormone; high trophic hormone
2o excess high trophic hormone and hormones of target gland
2o deficiency low trophic hormone and hormones of the target gland
3o deficiency low trophic hormone and hormones of the target gland

8. Assessment of Hormone Function
1. Direct measurement of hormone concentration
A. Basal serum hormone levels
B. Hormone measurement in the urine.
Urinary excretion of hormone or its metabolite
Corrects for fluctuations in blood levels
Integrates value over longer period
2. Dynamic tests
A. Suppressive tests for hormone excess
(DST; Glucose ST)
B. Stimulation test for hormone deficiency (Insulin Induced Hypoglycemia to evaluate Hypothal-PG axis
3. Image Studies p

9. Female estrogens/progesterones Male testosterone
Negative Feedback
Hypothalamus RF
ADH
Oxytocin
Anterior PG
Post. PG.
Thyroid
TSH
Multiple tissues of
the body T4 GH
ACTH LH
FSH T3
PRL
Ad. cortex
Breast
Gonads
Cortisol
Female estrogens/progesterones
Male testosterone

10. HYPOTHALAMIC HORMONES
REGULATION
PHYSIOLOGIC ACTION
Corticotropin
Releasing H
Negative feedback by ACTH and adrenal cortisol
Stimulates secretion of ACTH
Thyrotropin RH
Negative feedback by TSH and thyroid H
Stimulates secretion of TSH and prolactin

11. HORMONE
REGULATION
PHYSIOLOGIC ACTION
GH Inhibiting H
Positive feedback by GH
Inhibits secretion of GH and TSH
Gonadotropin RH
Negative feedback by FSH and LH
Stimulates secretion of FSH and LH
Prolactin IH
Positive feedback by prolactin, TSH, FSH, LH and GH
Inhibits secretion of prolactin, TSH, FSH, LH and GH
Growth H RH
(Somatocrinin)
Negative feedback by GH
Stimulates secretion of GH

12. ANTERIOR PITUITARY HORMONES

13. Adrenocorticotrophic H (ACTH)
Regulation:
Corticotrophic releasing hormone (CRH) causes secretion in response to biorhythms with circadian variation
Production is regulated by glucocorticoid concentration via the negative feedback mechanism
Physiologic action:
Stimulate secretion of adrenocorticoids
Glucocorticoids (cortisol)
Mineralocorticoid (aldosterone)
Androgens)
Causes sedation, increased pain threshold, autonomic regulation of respiration, BP and HR

14. Adrenocorticotrophic H ( ACTH )
Episodic secretion in respose to
1. Falling levels of active glucocorticoids
Cortisol ( predominant) 90% inactive bound to CBG(Cortisol binding globulin)
2. Stress
3. Cycles of sleeping and waking
Display circadian rhythm
Peak: bet 4 am and 8am
nadir: at midnight

15. Adrenocorticotrophic H
Patient preparation:
Stressful venipuncture inc levels
Specimen collection/handing:
Collected in prechilled plastic tubes with EDTA or heparin
Place immediately on ice
Store at -20 C within 15 min of collection

16. TSH or Thyrotropin Regulation: Physiologic Function:
TRH from hypothalamus causes secretion in response to low levels of thyroid hormones (T3, T4)
Physiologic Function:
Stimulates secretion of T3, T4

17. TSH
Serum TSH is single best screening test for thyroid fxn followed by FT4
Useful for evaluating both thyroid and pituitary function
Elevated serum level:
sensitive and specific indicator of primary HYPOTHYROIDISM
Normal or decreased level: secondary or tertiary hypothyroidism

18. Growth Hormone
AKA : somatotropin
Most abundant hormone of ant PG

19. Growth Hormone Regulation: Physiologic Function:
GHRH and GHIH regulates its secretion in response to
exercise
stress,
hypoglycemia
Amino acids
testosterone
estrogen levels
Physiologic Function:
Promotes growth of soft tissue , cartilage and bone
Stimulates Pr synthesis , fat and CHO metabolism

20. Growth Hormone Increase GH  gigantism in children
acromegaly in adults
Decrease GH in children  dwarfism

21. Secreted in pulsatile bursts with very short half life
single random determination ( limited usefulness)
24 hours hormone secretion level (better measurement)

22. Growth Hormone Patient preparation: Specimen:
Patient should be fasting
Complete rest for 30 min before collection.
Spikes occur 3 hr after meals, stress, or exercise and 90 min after onset of sleep,
Specimen:
Serum preferred; refrigerate immediately; stable at 2-8C for 8 hr.

23. Prolactin Hormone
Biochemical properties similar with GH and placental GH
Main target organ: adult female mammary gland

24. Physiologic Function:
Regulation:
Regulated by TRH, dopamine
Physiologic Function:
Increased in pregnancy, sucking
Initiates lactation ; growth of mammary tissues; controls osmolality, fat , CHO , Vit D metab and steroidogenesis in the ovary and testis

25. Effects :
Suppresses ovulation
Stimulates growth of prostate
Hypersecretion :
Females: hypogonadism , infertility, oligo/amenorrhea , galactorrhea
Males: inhibits testosterone secretion, decrease spermatogenesis , infertility and galactorrhea

26. Prolactin Hormone Levels fluctuate; fluctuations occur Q 95 min,
Long half life ( approx 50 min )
Physiologically stimulated by :
Pregnancy, breast feeding, sleep, dietary Pr, hypoglycemia, exercise and stress

27. Prolactin Hormone Patient Preparation: Collect 3-4 hr after awakening;
levels increased during sleep and peak in early morning.
Avoid emotional stress, exercise, ambulation, protein ingestion ( can increase levels).
Specimen:
fresh nonhemolyzed serum; stable at 4 C for 24 hr.

28. Follicle Stimulating and Luteinizining H
Regulated by GnRH from hypothalamus
Controls the functional activity of gonads
Exhibit episodic, circadian and cyclic variations– best to use serial blood tests or timed urine collection
Specimen:
Serum, plasma and urine acceptable;
Stable 8 days at room temp; two weeks at 4C

29. HYPOTHALAMIC-PITUITARY FUNCTION TESTS

30. Hyperpituitarism
Most are due to benign tumors that are autonomous and do not respond to negative feedback control
GHsecreted by pituitary adenoma is not suppressed by glucose
Exception to the rule of suppressibility:
Prolactinoma and Pit adenoma that secrete ACTH(Pituitary Cushing); both are partially autonomous

31. GH Excess: Acromegaly 1. Serum GH
Elevated basal or random levels in most acromegalics
Basal and random GH may also be inc in
Normal patients due to episodic secretion
Malnourished patients
Anorexia nervosa
Patients on estrogen therapy

32. Best test to confirm acromegaly:
Measurement of GH following a glucose load.
GH is normally suppressed to <2ng/ml one hour after a g glucose load.
Failure to suppress means a functioning pituitary adenoma

33. Pituitary Hyperpituitarism
2. Serum Somatomedin C
Synthesized mainly in the liver
Mediates most of the major growth promoting effects of GH
Involved in negative feedback regulation of Normal GH secretion
Serum level of SM-C is a good screening test for acromegaly
Basal SM-C is elevated in acromegaly
Maybe elevated in adolescents during the peripubertal growth spurt and during pregnancy

34. Hypopituitarism : GH deficiency
GH testing:
Shd be routinely included in evaluating children with short stature
Not indicated in adults suspected of hypopituitarism
Basal GH levels: not reliable to distinguish deficiency from normal;
Baseline measurement : fasting morning sample
Factors that increase GH secretion:
Low serum glucose, dopamine, exercise

35. Laboratory diagnosis : Hypopituatarism : GH deficiency
Screening tests for GH deficiency:
GH measurement after 15 min exercise
Measurement of somatomedin:
Laron Dwarf: normal GH but low somatomedin

36. Stimulation Test to confirm GH deficiency
Stimuli
1. Insulin
2. Arginine
3. L-dopa
4. Clonidine
GH should be measured every 30 mins for 2-3 hours
Normal: GH increment above baseline >5ng/ml or a maximal GH>7ng/ml
GH deficiency: failure to respond to at least two independent stimuli; hypothalamic or pituitary gland dysfunction

37. Stimulation test:
Insulin induced hypoglycaemia to investigate suspected GH deficiency.
Insulin decreases plasma glucose concentrations and in a normal person this stimulates the release of GH (A)
A reduced or absent response is seen in a GH deficient patient (B)

38. Stimulation Test to confirm GH deficiency
GH stimulation test (After CRH):
A CRH injection is given followed by measurement of the blood level
Normal: GH elevated
Hypopituitarism: no response

39. Feed back Bolus injection of releasing hormone PITUITARY GLAND
Hypothalamus
Feed back
Bolus injection of releasing hormone
PITUITARY GLAND
Measure Growth Hormone
No response or delayed peak response (60 mins vs 20 mins)

40. ADRENAL FUNCTION TESTS

41. Hormones of Adrenal Gland :
Hormones of adrenal cortex (adrenal corticosteroids) :
Glucocorticoid ( cortisol ) secreted by cells in zona fasciculata –
Mineralocorticoid ( aldosterone ) secreted by cells in z. glomerulosa-
Sex hormones (testosterone and estradiol ) secreted by cells in zona reticularis
Catecholamines (dopamine, epinephrine and NE) secreted by chromaffin cells of adrenal medulla

42. Glucocorticoid (Cortisol)
Physiologic action:
Affects metabolism of proteins, CHO and lipids
Stimulates gluconeogenesis by the liver, inhibits the effects of insulin and decrease the rate of glucose use in the cells
Regulation:
Secreted in response to stress and ACTH
Normally:
secretion higher in early morning (6-8am)
lower in the evening (4-6pm);
lowest at midnight
Cortisol excess (Cushing’s Syndrome and in patients under stress): loss of diurnal variation in secretion

43. Circadian rhythm of cortisol secretion

44. Feedback control of Adrenal Corticosteroid synthesis and release
Decreased blood levels of adrenal corticosteroids, stress
Hypothalamus secretes corticotrophin releasing hormone (CRH)
Hormone secretion suppressed via negative feedback
Ant Pit g gland secretes ACTH
Adrenal cortex secretes hormones (cortisol)

46. Corticosteroid Excess : Cushing Syndrome:
Hyperadrenalism with production of excess cortisol
Clinical Presentation:
1. Glucocorticoid Effects: “cushingoid habitus”, bone dimineralization, glucose intolerance
2. Mineralocorticoid effects: HPN, edema, hypokalemic alkalosis
3. Sex steroid effects: hirsutism, acne, amenorrhea, gynecomastia

48. Cushing Syndrome: Causes
Exogenous glucocorticoid therapy (most common cause)
Other causes:
1. ACTH Producing pituitary adenoma (60%)
( Cushing disease)
2. Glucocorticoid producing adrenal neoplasm(20%)
(adenoma or carcinoma)
3. Ectopic ACTH-producing neoplasm(20%)

49. Tests for Adrenal Hormone Function
1. Serum cortisol
-Secretion is episodic and pulsatile in response to ACTH
-Single determination neither specific or sensitive
-90-97% is bound to CBG or transcortin
- Elevated in adrenal hyperfunction (Cushing’s Sx)
- Decreased in adrenal hypofunction (Addison’s)
- Diurnal rhythm of cortisol secretion is lost in Cushing Sx and patients under stress

50. 2. Urine Free Cortisol (UFC):
**Glucocorticoids:
Degraded in the liver and excreted in the urine as Hydroxycorticosteroid (17-OHCS).
Urine 17 OHCS is an indirect measurement of excessive plasma Glucorticosteroid
-indirect measure of the cortisol production rate
-Normal: <90ug/24hr
- UFC> 250mg/24 hr is almost always due to Cushing Sx

51. 3. Dexamethasone Suppression Test
Dexamethasone: cortisol analoque that should suppress ACTH in normal person and reduce cortisol.
Rapid DST for screening (low Dose DST)
Administer 1 mg dexamethasone at 11pm; measure 8am the following day:
Normal: Suppressed cortisol <5ug/dl
No suppression in Cushing’s Sx: useful for screening

52. Dexamethasone Suppression Test
Normal person: dexamethasone will suppress ACTH secretion (feedback) and cortisol production is consequently reduced.
No suppression to low dose: Cushing Syndrome
Ectopic ACTH Syndrome: no suppression even to HDST
In pituitary- dependent Cushings only high doses may suppress ACTH secretion

53. Adrenal Function Test 1. Plasma ACTH level
Increased : pituitary tumors
ectopic ACTH producing tumors
Decreased: cortisol producing tumors in adrenals
exogenous hormones

54. Adrenal Function Test
2. Overnight HIGH DOSE DST:
Procedure: Administer 8mg at 11pm measure serum cortisol 8am before and on the morning following dexamethasone
ACTH producing adenoma : Suppression of cortisol to 50% of basal
Adrenal neoplasm or ACTH syndrome: No suppression of cortisol

55. Primary Adrenal Insufficiency (Addison’s Disease)
Deficiency of all adrenal steroids
Relatively rare
Results from progressive destruction of adrenals by local disease or systemic disorder

56. Adrenal Function Test for Adrenal Insufficiency
3. Metyrapone test
Metapyrone: Blocks 11 beta-hydroxylase in ad. cortex which reduces synthesis of cortisol hence stimulate synthesis of ACTH with proximal buildup of deoxycortisol in adrenal
Procedure:
1. Administer 3.0 mg metyrapone at midnight.
2. Measure cortisol and 11 deoxycortisol at am baseline
and post-metyrapone

57. deoxycortisol
Metapyrone
11-β Hydroxylase
Cortisol
Metapyrone: Blocks 11 beta-hydroxylase in ad. cortex which reduces synthesis of cortisol hence stimulate synthesis of ACTH with proximal buildup of deoxycortisol in adrenal

58. Metyrapone Test:
Normal response: fall in cortisol to <5ug/dl and increase in ACTH, 11 deoxycortisol and urinary 17-OHCS
Cushing’s Dse: Increase in 11-deoxycortisol levels
Adrenal tumors/Ectopic ACTH: 11-deoxycortisol fails to increase
Failure of cortisol to fall invalidates the test
Not routinely used, although maybe better than High dose DST

59. Adrenal Function Test
Cortisone Stimulation (Cosyntropin); ACTH Stimulation
Screening test; less time consuming; can be done on OPD basis
Cortrosyn (synthetic subunit of ACTH) have full stimulating effect of ACTH in healthy individuals
- failure to respond : adrenal insufficiency
Procedure:
1. Get 4ml fasting blood venous sample at 8am
2. Administer cosyntropin IM/IV
3. Get 4ml samples at 30 and 60 mins after

60. Mineralocorticoid (Aldosterone)
Regulation:
ALDOSTERONE (predominant mineralocorticoid) is secreted by cells in the zona glomerulosa in response to ANGIOTENSIN (mainly); and by ACTH (not significant)
Clinical effects
Retains Na and H20 accompanied by K depletion leads to excess intravascular volume HPN

61. Aldosterone Elevated levels (primary aldosteronism)
Conn’s disease ( aldosterone producing adenoma)
Elevated levels (secondary aldosteronism) because of extenal stimuli or greater activity in the RAS:
Salt depletion
Potassium loading
Cardiac Failure
Nephrotic syndrom
Diuretic abuse

62. Aldosterone Decreased levels of aldosterone: Aldosterone deficiency
Addison’s disease

63. Tests for hyperaldosteronism:
1. Basal level of plasma aldosterone
*limited diagnostic value
2. Urinary Aldosterone
3. Captopril Suppression Test
Angiotensin- converting enzyme inhibitor: decrease the renin-stimulated aldosterone production secondary aldosteronism; no response in primary aldosteronism

64. Test for hyperaldosteronism:
5. Aldosterone Suppression test (Isotonic Saline infusion)
Normal response  suppress aldosterone release by decreasing renin
Primary aldosteronism  lack of aldosterone suppression
6. Aldosterone Stimulation Test ( Sodium restricted from diet)
Normal response renin level increased
Primary aldosteronism slight or no response in renin level

65. Adrenal Insufficiency:
1. Serum cortisol decreased
2. Rapid ACTH stimulation test
3. Long ACTH stimulation test
4. Serum ACTH
Elevated in primary adrenal insufficiency
Decreased in secondary and tertiary
5. Metapyrone test

66. PHEOCHROMOCYTOMA: Cathecolamine Excess
1. Increased cathecolamines at all times.
Cathecolamines: either epinephrine or norepinephrine is increased and should be assayed separately.
Plasma norepinephrine >750pg/ml or
Epinephrine >100pg/ml are found in 90-95% of patients
2. Urine test
Vanyllmandelic acid
Total metanephrine
Fractionated cathecholamines

67. PHEOCHROMOCYTOMA: Cathecolamine Excess
3. Clonidine Suppression test:
Clonidine (alpha agonist)  decrease efferent symphathetic flow
Normal: Norepinephrine level within N range
Pheochromocytoma: exaggerated response

68. PHEOCHROMOCYTOMA: Patient Preparation
Blood should be drawn through a previously inserted catheter from a patient who is fasting, resting quietly and non-stressed.
If patient is to kept on antiHPN meds during resting
The least interfering agents shld be used:
diuretics.
Vasodilators, and
alpha or Beta adrenergic blockers.

69. THYROID DISORDERS

70. Thyroid function

71. Hormone Regulation TRH  TSH T4/T3 Regulate:
iodine uptake, organification
synthesis & release of thyroid hormone
T4/T3 Regulate:
basal metabolism, thermogenesis, lipogenesis
fetal CNS development

72. Regulation of thyroid hormone secretion
>99% of thyroid hormones are carried in plasma bound to protein
<1% is free & active
Thyroxin-binding protein (TBG) binds most of the T4 and T3
TBG is synthesed by liver, severe liver disease  TBG   TT4 due to  protein-bound T4
 Estrogen (ex. Pregnancy)   synthesis of TBG   total T4 due to  protein-bound T4
Albumin and pre-albumin also carry T4 and T3 in plasma

73. Thyroid Hormones Thyroxine (T4) Triiodothyronine (T3) Thyroid gland
t1/2: 8 days
Triiodothyronine (T3)
80% in Periphery
Liver/kidney remove iodine from T4
t1/2: days

74. Binding Proteins T4/T3 99% protein bound Prevents excess tissue uptake
Maintains accessible reserve

75. Protein* binding + 0.03% free T4 80%
20%
(10-20x less than T4)
Total T nM
Total T nM
T3RU/THBI
*TBG 75%
TBPA 15%
Albumin 10%

76. Thyroid Function Tests :
TSH T3 T4
FTI ( free thyroxine index ), FT4 ( free thyroxine )
TRH
TBG ( Thyroid binding globulin )

77. More T4 in serum (5.5 to 12.5 ug/dl) T3 in serum 9(100 to 200ng/dl)
T3 exerts the major hormone effects  thus more phyiologically significant
T4 converted by peripheral nonthyroidal tissues to T3
T4 may have no direct effect until converted to T3

78. THYROID FUNCTION TESTS
THYROID STIMULATING HORMONE (TSH)
Stimulated by TRH (from hypothalamus)
Serum TSH is single best screening test for thyroid fxn followed by FT4
Useful for evaluating both thyroid and pituitary function
Elevated serum level:
sensitive and specific indicator of primary HYPOTHYROIDISM
Normal or decreased level: secondary or tertiary hypothyroidism

79. Clinical Uses of TSH Screening for euthyroidism
Initial screening and diagnosis for hyperthyroidism (dec. to undetectable levels except in rare TSH-secreting pituitary adenoma) and hypothyroidism
Useful in early or subclinical hypothyroidism before the patient develops clinical findings

80. Clinical uses of TSH
Differentiate primary (increased levels) from central [pituitary or hypothalamic] hypothyroidism (decreased levels)
Monitor adequate thyroid hormone replacement therapy in primary hypothyroidism

81. TSH increased in : Primary untreated hypothyroidism
Hypothyroidism receiving insufficient thyroid hormone replacement therapy
Hashimoto thyroiditis

82. THYROID FUNCTION TESTS: Total T4 and T3
1. TOTAL THYROXINE(T4) ANDTRIIODOTHYRONINE(T3) LEVELS
Total thyroxine (T4) is a good index of thyroid fxn when TBG are normal
T3 level- in cases of hyperthyroidisn with normal or low T4: T4; useful in monitoring therapy

83. THYROID FUNCTION TESTS: Total Thyroxine ( T4)
High: hyperthyroidism and acute thyroiditis
Low: hypothyroidism and chronic thyroiditis
Affected by concentration of binding proteins (TBG)

84. THYROID FUNCTION TESTS: Total Serum T3 ( Triiodothyronine )
Elevated proportionately to T4 in hyperthyroidism
Decreased in hypothyroidism
T3 thyrotoxicosis ( 5% of ind.) T3 elevated while T4 is normal
Not routinely measured except to monitor tx of T3 thyrotoxicosis

85. THYROID FUNCTION TESTS: Thyroxine Binding Globulin
A glycoprotein: synthesized in the liver
Principal serum carrier for T4 ( 75% ) and T3
Less than 1% of T3 and T4 are in the free form which determines function
Estrogen influences thyroxin binding
Phenytoin, coumarin, heparin clofibrate and aspirin compete with T3 & T4 for TBG binding sites
Measurement is rarely indicated

86. T3 Uptake Indirect measurement of unsaturated TBG in blood
Determination is expressed in arbitrary terms is inversely proportional to the TBG
Low T3U is indicative of conditions where there is elevated levels of TBG uptake

87. T3 Uptake
Hypothyroidism: insufficient T4 to saturate TBG unbound TBG is elevated and T3U values are low
Pregnant patients: TBG are increased proportionately more than T4 levels high levels of unbound TBG reflected in low T3U values
Useful only when T4 is done
Used to calculate FTI or F7

88. T3 Uptake
Procedure:
Known amount of radiolabeled T3 is added to test serum
Available binding sites in test serum combine with labeled T3 inversely proportional to the amount of endogenous T4 already bound

89. Low endogenous T4 (hypothyroid)  many TBG sites free to react with labeled T3—measured residual radiocativity is low
High endogenous T4 (hyperthyroid)  few TBG sites free to react with labeled T3 measured residual radioactivity is high

90. Resin is used to measure residual radioctivity
Low residual activity—numerous binding sites unoccupied( low endogenous T4)
High residual activity—few binding sites unoccupied( high endogenous T4)
Results are expressed as % radioactivity left unbound
Hyperthyroidism: both T4 and T3U high values
Hypothyroidism: both T4 and T3U have low values

91. THYROID FUNCTION TESTS: FREE THYROXINE INDEX
Correlates better with clinical status
in the presence of abnormalities in TBG
Calculated as the product of absolute thyroid hormone and the binding capacity of TBG
FTI= Measured FT4 (T4 x Value of T3 Uptake)
(Reference Interval=1-4.2)
Normal in pregnancy;
low in hypothyroidism;
high in hyperthyroidism

92. Thyroid Function Tests
Hyperthyroidism
Hypothyroidism
Total T3 & T4 in serum
Increased
Decreased
Free thyroxine index
Serum TSH

93. Interpreting Thyroid Function Tests

94. Clinical patterns of thyroid disease
Hyperthyroidism-
Lab: excessive levels of TH ( T3 , T4 ) ;
S/sx: heat intolerance, palpitation, weight loss, tachycardia tremors
Causes: Graves Ds, toxic adenoma, toxic goiter , TSH secreting pituitary adenoma

95. Hypothyroidism –
Lab: decrease levels of TH
S/sx: Bradycardia, cold sensitivity, dry skin, muscle weakness , myxedema, cretinism
Causes : TG ablation and destruction ( primary ) ; pituitary hypofuncytion of TSH (secondary )

96. Laboratory Diagnosis of Thyroid Disease
1 thyroid dis. is abnormality in the thyroid gland
TRH and TSH level just reflect N feedback response
2 thyroid dis. is really an abnormality in pituitary gland which cause error in amount of TSH produced
T4 and T3 conc’n just reflect N feedback response
3 thyroid dis. is abnormality in hypothalamus causing error of TRH produced
Both TSH and T4 & T3 levels just reflect N feedback response

97. Measuring trophic hormones and hormones of the peripheral endocrine gland
High TSH - Low T3/T4 1o Hypothyroidism Low TSH - High T3/T4 1o Hyperthyroidism Low TSH - Low T3/T4 2o

98. “Euthyroid Sick Syndrome”
Severe illness often results in low serum levels of T3 and T4
Causes:
1. Decreased in serum pre albumin in severe illness decrease in hormone binding capacity
2. Fall in amount of T4 deiodinatd to T3 with increase in the metabolic pathways leadig to the inactive product reverse T3
Diagnosis: demonstrating normal TSH level.