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55 Cards in this Set
- Front
- Back
What is the predominant thyroid product?
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T4 (90-95%)
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What is the rate limiting step when TSH is high?
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iodine rate
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What is the active thyroid hormone?
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T3
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How is t3 transported peripherally?
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99.7% protein bound, inactive, unregulated
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Where is most T3 produced?
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Liver and kidney by action of monodeiodinases
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What is the clinical significance of normal total T4 and T3 levels?
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It effectively rules out thyroid disease (central 75%)
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What is euthyroid sickness?
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Conversion of T4 to T3 is inhibited. This causes normal total and free T4, normal T3RU, decreased T3 and normal TSH.
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What is the most important test for evaluating for thyroid disease?
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TSH
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How does T3 resin uptake testing work?
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Labeled T3 is bound to the patient's serum. The excess labeled T3 is bound to a resin, and that is measured and is inversely proportional to the amount of TBG binding sites available in the patients serum.
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What is the normal amount of available TBG binding sites?
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40% free
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What is the status of T4 and T3 resin uptake in hyperthyroid?
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Both increased. Hyperthyroid means less available binding sites on TBG, means more label taken up in the resin
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What is the status of T4 and T3 resin uptake in hypothyroid?
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Decreased T4 and resin uptake
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What is the status of T4 and T3 resin uptake in patients with a high level of TBG?
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Increase T4 and decrease resin uptake
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What is the status of T4 and T3 resin uptake in patients with a low level of TBG?
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Decreased T4 and increased resin uptake
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What antibody is specific for graves disease
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thyroid stimulating immunoglobulin
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When is thyroglobulin useful?
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As a thyroid tumor marker
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What is the first finding in hyperthyroidism?
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Suppressed TSH
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What gets elevated first in graves?
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T3 before t4, free before total, normal t3 suggests another cause
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What is the first finding in hypothyroidism?
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Increased TSH, usually > 50 mU/Lfollowed by
low free, total, t3RU |
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How does pregnancy affect thyroid values?
TBG, T3, total t4, free t4, resin uptake? |
High total t4 and T3, low t3 resin uptake, normal TS, normal free t4
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How does cirrhosis/nephrotic syndrome affect thyroid values?
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Low total t4, high T3RU, normal TSH, normal free t4
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How does acute illness change thyroid values?
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Decreased t3 (low peripheral conversion), normal total/free t4, tsh
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Explain the cyclic production of glucocorticoids
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Highest on waking, lowest in early sleep
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How does stress affect cortisol?
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Stimulates IL-6 and serotonin, minimizes cyclic production, Increased Cortisol and ACTH
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What stimulates cortisol production?
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ACTH
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True or false, cortisol is mostly protein bound
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True
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How is urine free cortisol affected by hypercortisolism?
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Increases exponentially over serum concentration
plasma 2x, urine 50x normal |
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What urine metabolite measures androgens (not testosterone)
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17 ketosteroids. By colormetric assay
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What urine metabolite measures cortisol, precursor, and metabolites
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17-hydroxysteroids. By colormetric assay
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What is cushing disease?
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Pituitary ACTH production
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ACTH undetectable or low, cortisol, is not suppressed by high or low doses. Diagnosis?
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Primary Hypercortisolism
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Explain pituitary stimulation
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Metyrypone blocks 11 hydroxylase, normal response is for cortisol to fall, but ACTH and 11 deoxycortisol to rise by at least 7
A more sensitive test (but more dangerous!) is for insulin hypoglycemia to stimulate ACTH and cortisol levels to >18-20 |
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What is another name for T4? |
free thyroxine |
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What two antibodies do you find elevated in Hashimoto's Disease? |
anti-microsomal or anti-thyroid peroxidase (anti-TPO) |
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What 3 antibodies do you find elevated in Graves? Which one is specific for Graves? |
1) anti-microsomal 2) anti-thyroid peroxidase 3) anti- thyroid stimulating immunoglobulins (TSI) - this is specific for Graves |
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what is the single best test for detection of hyperthyroidism? |
TSH |
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what is the single best test for detection of hypothyroidism? |
TSH |
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What can increase the TBG? |
active liver injury, pregnancy and many drugs including estrogens, estrogen dominent OCP, phenothiazines and opiates |
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what can decrease the TBG? |
protein losing states, cirrhosis, congenital deficiency |
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What stimulates the production of cortisol? |
stress, inflammation (IL-6), darkness, serotonin, hypoglycemia |
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what inhibits the production of cortisol? |
light, glucose, synthetic steroids such as dexamethasone |
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what are 2 false positive for the dex suppression test? |
obesity (most of the drug goes into the fat), increased liver metabolism (by other drugs like alcohol and pheytoin) and renal failure (may not absorb dex) |
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for adrenal stimulation tests, what do you give? |
cortosyn or cosyntropin. A serum cortisol increase to >18-20 confirms intact adrenal |
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describe the dex suppression test |
1) overnight, do screen. Give 1mg and expect the serum cortisol to be <3 in a normal person 2) Give low dose 0.5mg. If the URINE cortisol <10, then it is not cushing. If the URINE cortisol >10, then maybe cushing 3) give high dose. This is to find out if the patient has a pituitary problem. If there is a FALL in the URINE free cortisol <20% or the SERUM free cortisol <50%, then the patient has pituitary problem (cushing DISEASE) 4) If the patient didn't have a fall in cortisol, then measure ACTH. If there is high ACTH, it is ectopic cortisol production. If there is low ACTH, then there is an adrenal tumor. |
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what is addison's disease? |
primary adrenal failure. |
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What test do we do to distinguish primary from secondary adrenal insufficiency? |
measure cortisol before and after stimulation with cortrosyn If cortisol is low, high ACTH confirms primary adrenal insufficiency, while low ACTH is seen in secondary (or tertiary) adrenal insufficiency |
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Congenital adrenal hyerplasia: which have HTN? virilization? |
deficiencies that begin with the number 1 have HTN (e.g. 11 hydroxylase and 17 hydroxylase) Deficiencies that end with number 1 have virilization (e.g. 21 and 11 hydroxylase) |
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in 21-hydroxylase deficiency, what s the compound that accumulates? |
17-OH Progesterone |
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When are renin and aldosterone at their lowest levels? highest? |
lowest in morning and in supine position highest in afternoon and in upright position |
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how must renin samples be handled? |
room temperature to prevent false increases hypokalemia inhibits aldosterone production and should be corrected prior to testing aldosterone or renin levels |
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What stimulates renin production? |
decreased blood flow, decreased urine sodium, diuretics, allowing specimen to sit at 4C (artifact), hyperkalemia |
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what inhibits renin production? |
NSAIDS, beta blockers, ACE inhibitors, hypokalemia, heparin, atrial natriuretic hormone, adrenal disease |
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what are the renin and aldosterone levels for primary and secondary hyperaldosteronism? |
primary: decreased renin and increased aldosterone secondary: increased renin and increased aldosterone |
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what can increase catecholamines? |
stress and caffeine. prolonged excess of catecholamines adernal medulla tumor such as neuroblastoma or pheochromocytoma |
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what do we measure for neuroblastoma? |
HVA and VMA |