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Thyroid Function tests

Thyroid Function tests

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Thyroid Function tests

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  1. Thyroid Function tests Dr Danielle B Freedman please see January 2015 PULSE p 50 - 51 April 2018

  2. Incidence of Thyroid disease Hypothyroidism • Spontaneous 2%, 10 Females : 1 Male • Another 1% due to destructive treatment for Hyperthyroidism • Congenital Hypothyroidism 1/4000 births Hyperthyroidism • 0.5 – 2%, 10 Females :1 Male

  3. Important Clinical Manifestations Hyperthyroidism • 5-10% of patients with thyrotoxicosis have Atrial Fibrillation • Correctable cause of osteoporosis • Associated with menstrual irregularity, subfertility and foetal loss Hypothyroidism • Well recognised secondary cause of hyperlipidaemia • Associated with menstrual irregularity, subfertility and foetal loss

  4. Causes of Hyperthyroidism • Grave’s disease • Toxic Mutinodular goitre • Solitary toxic adenoma • Thyroiditis • Exogenous iodine and iodine-containing drugs eg amiodarone • Excessive T4 or T3 ingestion • Ectopic thyroid tissue, eg struma ovarii, functioning metastatic thryoid cancer • hCG dependent: choriocarcinoma • TSH dependent: pituitary tumour Account for >90% cases

  5. Causes of hypothyroidism • Atrophic hypothyroidism (may represent the end-stage of Hashimoto’s disease) • Automimmune hypothyroidism (Hashimoto’s thyroiditis) • Post-surgery, radioactive iodine, anti-thyroid drugs (eg carbimazole) and other agents (eg lithium) • Congenital • Dyshormonogenic • Secondary (pituitary or hypothalamic disease) • Iodine deficiency Account for >90% cases

  6. Drugs and thyroid disease Amiodarone • Hyperthyroidism (iodine deficient) 10% • Hypothyroidism (iodine replete) 20% Lithium • Hypothyroidism: Mild 34% Overt 15% Monitoring for patients taking either drug • 6 monthly TFT’s • 12 monthly review

  7. Patients on Levothyroxine • Annual measurement TSH (+FT4) • Starting dose 50 mcg • Check TFT’s 6-8 weeks after commencing treatment and following change of dose • Dose increment 25 mcg • Average dose 1.6 mcg/kg • Caution with elderly patients – start @25mcg In pregnancy • Increase dose by 50 mcg • Measure TFT’s each trimester • TSH should be 1.0- 2.5 mU/L

  8. Patients on Carbimazole • If patient toxic refer to Endocrine clinic /start Cz 20mg bd, ? Beta blockers • TFTs checked every 4 – 6 weeks • Once stable ,every 2 – 3 months • Other investigations, anti-TPO abs and US • Duration, 18 months – 2 years

  9. Thyroid disorders in pregnancy and the post partum period

  10. Introduction • 4% of pregnant women: • Have a history of thyroid disease • Develop thyroid disease during pregnancy • 1st time develop thyroid disease within 5 years following pregnancy • Beware ‘Gestational transient thyrotoxicosis’- hCG induced hyperthryoidism – TSH receptor sensitivity to (appropriately) high hCG concentrations • Remember the reference range for Free T4 and Free T3 decreases approx 20% in the 2nd and 3rd trimesters • During pregnancy TSH can be up to 50% lower in the 1st trimester and within the non-pregnant reference range in the 2nd and 3rd trimesters, while Free T4 can be up to 20% lower in the 2nd and 3rd trimesters and within the non-pregnant reference range in the 1st trimester based on current scientific evidence. • ATA & AACE do NOT recommend universal screening for thyroid function in pregnancy

  11. Hypothyroidism in pregnancy • 2-3% of iodine-sufficient pregnant women will have undiagnosed hypothyroidism – mostly subclinical • Main cause in iodine sufficient is chronic autoimmune thyroiditis • 10-20% of women of child bearing age have positive anti-TPO antibodies • Untreated overt hypothyroidism is associated with: • Increased risk of miscarriage • Preterm delivery • PET • Neonatal mortality • Low birth weight • Decreased IQ

  12. Treatment and monitoring in pregnancy • ATA recommend diagnosis of hypothryoidism in all pregnant women with; - a TSH > reference interval and a low FT4 • - All with TSH > 10mU/L irrespective of FT4 • In women with subclinical hypothryoidism who are not initially treated; ATA recommends monitoring FT4 and TSH every 4 weeks until 16-20/40 and once between 26/40 - 32/40 weeks gestation • Dosage of levothyroxine will go up during pregnancy ( 30-50%) • Aim for TSH 1.0 – 2.5 mU/L, monitor TSH as above • Post partum revert back to original dosage and check TFT’s 6 weeks post partum

  13. Thyrotoxicosis in pregnancy • Grave’s disease occurs in 0.1-1% of all pregnancies • Transient gestational hyperthyroidism can occur in the 1st trimester (prevalence 2-3 %) • In patients with Grave’s: • Monitor TFT’s every 4-6 weeks • TRAb at 24 weeks – can cross the placenta and cause foetal and neontalhyperthryoidism (<1%) • Uncontrolled Grave’s: • Foetal loss • PET • Miscarriage • Premature labour • CCF • Thyroid storm

  14. Treatment of thyrotoxicosis in pregnancy • 1st trimester PTU • 2nd and 3rd trimester PTU/CBZ • Block replacement and I131: CONTRAINDICATED • Aim to keep: FT4 in within or slightly above reference range TSH within the reference range • 30-40% of women are able to remain euthyroid without treatment in the last few weeks of pregnancy • Can relapse post partum • Breast-feeding is ok if the dose of PTU < 300mg/day CBZ < 30 mg/day

  15. Post partum thyroiditis • May be difficult to distinguish from Grave’s • 4-9% of women develop post partum thyroiditis • Positive Anti-TPO antibodies (which rise in titre 6 weeks PP) • Can be transiently hyperthyroid (unless Grave’s) – do not treat with antithyroid drugs • Can become transiently hypothryoid or permanent (20 - 30%) • If ‘transient’ check TFT’s annually – can recur with subsequent pregnancy

  16. Development of thyroid dysfunction in the postpartum period

  17. Adapted from the ACB/RCPath ‘Minimum Retesting Intervals’ 2016

  18. 1 • 58 year old male with strong FHx of CHD. Non-smoker with BMI = 26.5. • Fasting glu = 4.6 mmol/L • Chol = 8.4 mmol/L • HDL = 1.1 mmol/L • Trig = 2.1 mmol/L • 1/52 – complaining of malaise • CK = 850 U/L [<170]

  19. What test(s) are required to investigate the raised CK ? a. Magnesium b. FBC c. TFT’s d. HbA1c e. U+E

  20. a. TFT

  21. 2. • Which one of the following findings in a patient with primary hypothyroidism could notbe explained by this condition ? • a). Hyponatraemia • b). Increased mean red cell volume • c). Plasma cholesterol of 7.2 mmol/L • d). Plasma ALP 2x the ULN • e). Plasma CK 2x the ULN

  22. d). Plasma ALP 2x the ULN

  23. 3. 25-year-old female with menorrhagia FT4 = 11.5 pmol/L [10 – 20] TSH = 8.3 mu/L [0.4 – 4.5] What do you do next? • Repeat in 3 months • Measure serum anti-TPo abs • Treat with levothyroxine • Measure 9 am Cortisol

  24. Answer • Repeat in 3 months • Anti TPO abs

  25. 4. Mr DW Home visit dob 20/8/41 LVF A fibrillation PMH CABG 1989 Angioplasty 2004 MI – 1998 Hypertension Hypercholesterolaemia Type 2 DM

  26. DH Frusemide Clopidogrel Nicorandil Amiodarone Simvastatin Ezetimibe Warfarin Ramipril Bisoprolol Allergies None SH Ex smoker Occasional alcohol Lives with wife FH none

  27. O/E p = 130 AF bp = 143/76 chest basal crackles JVP  5 cm No ankle oedema HS I and II and 0

  28. U = 10.7 mmol/l [2.5 – 6.5] Cr = 124 mmol/l [60 – 120] Na = 131 mmol/l K = 3.6 mmol/l FT4 = 100.2 pmol/l [12 – 23] TSH = <0.06 mu/l [0.35 – 5.5]

  29. QuestionIn addition to treating his AF and LVF, how do you think the patient’s deranged thyroid function should be treated? interactive • Do nothing • Stop Amiodarone • Start Propylthiouracil • Treat with radioactive iodine

  30. Answer • Stop Amiodarone • PTU

  31. 5. • 81 yr old female just discharged from hospital with diagnosis of pneumonia. • FT4 = 9 pmol/l (10-20) • TSH = 0.10 mu/l (0.4-4.5) • FT3 = 1.8 pmol/l (3.0-8.0)

  32. What would you do next ? • a) Nothing • b) Treat with carbimazole • c) Treat with levothyroxine • d) repeat TFTs in 4 weeks

  33. 6. • 45 yr old female on 125mcg levothyroxine c/o TAT • FT4 = 13pmol/l ( 12-23) • TSH = 4.3 mu/l ( 0.35 – 5.5 )

  34. What would you do? • a) Nothing • b) reduce T4 to 100mcg • c) Increase T4 to 150mcg • d) rpt TFTs in 2 months

  35. 7. • 65-year old man • c/o TATT, muscle aches, loss of libido • DH nil Sodium 137 mmol/L Potassium 4.2 mmol/L Creatinine 76 umol/L eGFR >60 ml/min/1.73m2 TSH 1.32 mU/L Testosterone 0.5 nmol/L Creatine Kinase 223 U/L Hb 138 g/L

  36. Free T4 5.5 pmol/L Duty Biochemist added: • Cortisol 52 nmol/L • LH 1.2 U/L • FSH 0.8 U/L Diagnosis?

  37. What most determines a clinician’s test ordering? 1. Fear of litigation 2. Cost of test 3. Evidence based guidelines 4. Patient went to Lab Tests Online 5. Watched an episode of ‘House’ last night

  38. ACB SPOTLIGHT MEETING

  39. Analysis of malpractice claims – USAnn Intern Med 2006; 145: 488-496 Faulty process leading to missed diagnosis: • Failure to order appropriate dx /lab test 55% • Inappropriate/inadequate follow-up 45% • Failure to obtain adequate history/exam 42% • Incorrect interpretation of diag. test 37% • Failure to refer 26% • Provider did not receive test results 13% • Tests ordered but not done 9% • Tests performed incorrectly 8%

  40. Patient Safety and Laboratory Medicine Pre Analytical right test right patient right label ‘request form’ right sample Analytical right lab EQA right conditions - Accreditation (CPA) temperature Post Analytical right result right patient right clinician right communication right interpretation right Mx and further investigations

  41. 17.4 % of US GDP was spent on health care in 2009 $65 billion per annum on > 4.3 billion laboratory tests How much is spent in the US on unnecessary testing and procedures a. $ 1.5 billion b. $ 3.0 billion c. $ 6.8 billion d. $ 18.0 billion