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ENDOCRiNE FUNCTION TESTS

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

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ENDOCRiNE FUNCTION TESTS

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  1. ENDOCRiNEFUNCTION 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. 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;lowtrophic 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

  9. 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

  11. ANTERIOR PITUITARY HORMONES

  12. 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

  13. 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

  14. 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

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

  16. 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

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

  18. Growth Hormone • Regulation: • 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

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

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

  21. Growth Hormone • Patient preparation: • 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.

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

  23. 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

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

  25. 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

  26. 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.

  27. 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

  28. HYPOTHALAMIC-PITUITARY FUNCTION TESTS

  29. 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

  30. 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

  31. Best test to confirm acromegaly: • Measurement of GH following a glucose load. • GH is normally suppressed to <2ng/ml one hour after a 75 -100g glucose load. • Failure to suppress means a functioning pituitary adenoma

  32. 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

  33. 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

  34. 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

  35. 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

  36. 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)

  37. 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

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

  39. ADRENAL FUNCTION TESTS

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

  41. 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

  42. Circadian rhythm of cortisol secretion

  43. 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)

  44. 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

  45. 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%)

  46. 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

  47. 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

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