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Endocrine Lab Tests Sarah Lewis 12/12/24Use code CBOSCECREW24 at checkout on geekyquiz.com for 10% off OSCE flashcards, OSCE stations and knowledge bundles. Objectives - To be able to interpret endocrine lab test results (TFTs, PTH, adrenal hormones) - To be able to suggest appropriate differentials based on endocrine lab test results - To practice OSCE stations involving interpretation of endocrine lab test results (breakout rooms)Thyroid Function Tests (TFTs) What’s in a TFT? Blood test - Thyroid stimulating hormone (TSH) - Free T3 - Free T4 (thyroxine) TSH made by (anterior) pituitary, T3 and T4 by thyroid gland Free T4 is a more ‘relevant’ marker than T3 - thyroid makes T4:T3 in a 20:1 ratio ‘Free’ = not bound to a protein in the blood What do they do? TSH - tells thyroid to make more thyroid hormone. - Negative feedback loop from thyroid - ‘Opposite’ from what you’d expect? T3 - active thyroid hormone, acts peripherally T4 - main thyroid hormone produced by thyroid gland - ^^ What you’d expect[Text slides] Conditions to be aware of - TFTs Hyperthyroidism (know common causes) - Low TSH, high T3/T4 Hypothyroidism (know common causes) - High TSH, low T3/T4 Subclinical hyper/hypo - there’s something going on, but its not having an effect (yet?) - T3/T4 normal, but TSH low (hyper) or high (hypo) Primary vs secondary - Primary - problem comes from the thyroid - Secondary - not the thyroid’s fault! - If BOTH TSH & T3/T4 are ‘in agreement’ i.e. they’re both high = secondary How to approach TFT interpretation OSCE Scenario - questions at the end of the thyroid examination station, or after a history station on hyper/hypothyroidism? - Look at T3/T4 result first - this is ‘What you’d expect’ & might help avoid confusion! - If high = hyper, if low = hypo - If normal - could be subclinical - Look at TSH - is this opposite or the same as the T3/T4 level? - Opposite = primary - The same = secondary Example You have just performed a perfect thyroid examination on a patient. The examiner passes you a sheet of paper with the following lab results: - T4 & T3 are normal - TSH is low, therefore… TFTs - now what? Examiners might ask you what your next steps would be - Thyroid exam (if not already done)? - Other bloods - e.g. TSH receptor autoantibodies in Graves, anti-TPO & thyroglobulin antibodies in Hashimotos - Drug management - revise! - Repeat bloods - TFTs can be repeated after 4-6 weeksParathyroid hormone (PTH) What is PTH? Parathyroid hormone, made by parathyroid glands (near thyroid) Tells serum calcium to go up, by targeting: - Bones (osteoclasts) - Kidneys (don’t pee out calcium) - Intestines (increase vit. D activity, so more calcium absorption) - PTH converts vitamin D into active form, so it can absorb more calcium Low serum calcium = more PTH secreted High serum calcium = less PTH secreted[Text slides] Conditions to be aware of - PTH Hyperparathyroidism (primary, secondary, tertiary) :-( - Primary: Too much PTH secreted, usually by parathyroid tumour - Secondary: Low vit D/CKD causes reduced calcium absorption, causing overactivity of gland (as low serum ca) - Tertiary: Secondary hyperparathyroidism for a long time, causes hyperplasia. Cause is then fixed, but hyperplasia isn’t - so hyperactive gland. Hypoparathyroidism? Interpretation - PTH & calcium PTH is high (hyperparathyroidism) PTH Serum calcium Primary High High Secondary High Low/normal Tertiary High High - History differentiates between primary & tertiaryExampleAdrenal hormones (tests for Cushing’s & adrenal insufficiency) What are the adrenal hormones? - Cortisol - Aldosterone - Sex hormone precursors - Adrenaline & noradrenaline Each secreted from different parts of the gland: Conditions to be aware of - adrenals Cushings syndrome - (Main cause - iatrogenic) - Others - ACTH dependent/ independent - ACTH dependent = ACTH is what is causing the rise in cortisol. Pituitary adenoma secreting ACTH (Cushing’s disease), ACTH production from a tumour - ACTH independent = cortisol being produced too much - adrenal adenoma (secreting cortisol) and carcinoma, adrenal hyperplasia Adrenal insufficiency - Primary (Addison’s disease) & secondary - Primary = problem with adrenal gland - Secondary = problem with stimulation of adrenals from pituitary Cushings tests - Cushings = too much cortisol Dexamethasone suppression test - low and high dose - Low dose - Cushing’s syndrome or not? - High dose - differentiate between pituitary disease/ectopic or adrenal cause - Dex suppresses pituitary gland, via -ve feedback - Normal = dex will reduce cortisol - Pituitary adenoma (Cushing’s disease) - low dose will not reduce cortisol, but high dose will “within HPA axis still” - Exogenous ACTH/adrenal cause - low and high dose dex have no effectCushings tests (pt 2) Cushing’s tests - now what? Pituitary adenoma (Cushing disease) - MRI pituitary. If inconclusive - inferior petrosal sinus sampling - compares ACTH conc. In the sinus to serum ACTH - Large difference = ACTH-secreting adenoma Adrenal adenoma/carcinoma - CT abdomen Ectopic ACTH - CT thorax - bronchial tumours, SCLC Adrenal insufficiency tests Short synacthen test - gives synthetic ACTH & sees if it stimulates adrenal glands. - Cortisol measured before, 30 mins and 60 mins after - Cortisol rises (2x) = normal - No rise in cortisol = adrenal insufficiency Primary/secondary adrenal insufficiency - serum ACTH - Primary: high ACTH - Secondary: low ACTH Summary - Testing for adrenal insufficiency Serum cortisol after short Serum ACTH Synacthen test Normal Increase (at least 2x) Normal Primary adrenal Little/no increase High insufficiency Secondary adrenal Little/no increase Low insufficiency Adrenal insufficiency tests - now what? Primary insufficiency - Antibodies** can be raised in autoimmune cause Secondary insufficiency - MRI pituitary - History may be suggestive? E.g. trauma, radiotherapy or surgery to the pituitary Other electrolyte abnormalities - hyponatraemia, hyperkalaemia, hypoglycaemia, raised creatinine and urea due to dehydration (hypotension) Final thoughts / any questions? Phaeochromocytoma - too much adrenaline Conn’s syndrome - too much aldosterone ^^ hypertension References Geeky Medics. Thyroid function test interpretation [Internet]. Geeky Medics; 2018 Apr; [updated 2024 Sep; cited 2024 Dec]. Available from: https://geekymedics.com/thyroid-function-test-tft-interpretation/ MedSchool. Thyroid function tests quiz [Internet]. MedSchool; c2023; [cited 2024 Dec]. Available from: https://medschool.co/quizzes/tft Zero to Finals. Hyperparathyroidism [Internet]. Zero to Finals; c2024 [cited 2024 Dec]. Available from: https://zerotofinals.com/medicine/endocrinology/hyperparathyroidism/ Cleveland Clinic. Hyperparathyroidism [Internet]. Cleveland clinic; [updated 2024 Feb; cited 2024 Dec]. Available from: https://my.clevelandclinic.org/health/diseases/14454-hyperparathyroidism PassMedicine. Hyperparathyroidism questions. PassMedicine; [cited 2024 Dec]. Available from: https://passmedicine.com/ Geeky Medics. Multiple myeloma [Internet]. Geeky Medics; 2014 Jan [cited 2024 Dec]. Available from: https://geekymedics.com/multiple-myeloma/ Geeky Medics. Cushing’s syndrome [Internet]. Geeky Medics; 2020 Mar [cited 2024 Dec]. Available from: https://geekymedics.com/cushings-syndrome/ Zero to Finals. Cushing’s syndrome [Internet]. Zero to Finals; c2024 [cited 2024 Dec]. Available from: https://zerotofinals.com/medicine/endocrinology/cushings/ Zero to Finals. Adrenal insufficiency [Internet]. Zero to Finals; c2024 [cited 2024 Dec]. Available from: https://zerotofinals.com/medicine/endocrinology/adrenalinsufficiency/ (Extras) - Zero to Finals - phaeochromocytoma https://zerotofinals.com/medicine/endocrinology/phaeochromocytoma/ and Zero to Finals - hyperaldosteronism https://zerotofinals.com/medicine/endocrinology/hyperaldosteronism/