UK Guidelines For The Use Of Thyroid Function Tests
UK Guidelines for the Use of Thyroid Function TestsJuly 20061
ContentsGuidelines development groupNotes on the development and use of the guidelinesTypes of evidence and the grading of recommendationsAbbreviationsPresentation oduction1.1 Thyroid disease1.2 Thyroid function tests1.3 The patient perspective1.4 The physician perspective1.5 The laboratory perspective1.6 The need for national guidelines111111121212Indications for thyroid function testing2.1 Introduction2.2 Screening for thyroid dysfunction2.2 Surveillance of thyroid function2.3 Monitoring of thyroid function15152022Hypothyroidism3.1 Primary hypothyroidism3.2 Subclinical (mild) hypothyroidism3.3 Secondary hypothyroidism3.4 Congenital hypothyroidism24272830Hyperthyroidism4.1 Primary hyperthyroidism4.2 Subclinical (mild) hyperthyroidism4.3 Inappropriate TSH323637Thyroid function in pregnancy5.1 Introduction5.2 Hypothyroidism5.3 Hyperthyroidism5.4 Post-partum thyroiditis5.5 Screening for thyroid disease during pregnancy5.6 Neonatal thyroid assessment393940424243Thyroid function testing in thyroid cancer6.1 Introduction6.2 Differentiated thyroid cancer6.3 Medullary thyroid cancer6.4 Anaplastic thyroid cancer464649512
Contents (continued)7.8.Laboratory aspects of thyroid function testing7.1 Introduction7.2 Biochemical investigations for thyroid function7.3 Tests to establish if there is thyroid dysfunction7.4 Selective use of thyroid function tests7.5 Reference ranges7.6 Quality control and quality assurance7.7 Interpreting results of thyroid function tests7.8 Follow-up of unusual test results7.9 Laboratory tests used to determine the cause of thyroid dysfunction7.10 Recommended protocol for determining functional sensitivity7.11 Drugs that alter thyroid hormone synthesis, secretion & metabolism5252525455565761616666Areas for further studies68Appendix 169References3
Use of thyroid function tests: guidelines development groupWorking party membershipProfessional body representedGraham H Beastall BSc, PhD, FRCPathSecretary, guideline development groupConsultant Clinical Scientist, GlasgowAssociation for Clinical BiochemistryGeoffrey J Beckett BSc, PhD, FRCPathReader in Clinical Biochemistry, EdinburghJayne Franklyn MD, PhD, FRCP, FMedSciBritish Thyroid AssociationProfessor of Medicine, BirminghamWilliam D Fraser MD, MRCP, FRCPathAssociation for Clinical BiochemistryProfessor of Clinical Biochemistry, LiverpoolJanis HickeyBritish Thyroid FoundationPatient representative. Founder and Director of BTFRhys John BSc, PhD, FRCPathConsultant Clinical Scientist, CardiffAssociation for Clinical BiochemistryPat Kendall-Taylor MD DCH FRCPBritish Thyroid AssociationEmeritus Professor of Endocrinology, Newcastle Upon TyneBetty NevensBritish Thyroid FoundationPatirnt representative. Office Manager for BTFMark Vanderpump MD, FRCPBritish Thyroid AssociationConsultant Physician, Royal Free Hospital, London4
Notes on the development and use of the guidelinesThe guidelines development groupThe Use of Thyroid Function Tests Guidelines Development Group was formed in2002 under the auspices of the Association for Clinical Biochemistry (ACB), theBritish Thyroid Association (BTA) and the British Thyroid Foundation (BTF).Purpose of the guidelinesIt is hoped that the document will provide guidance for primary care physicians,specialist physicians, endocrinologists, and clinical biochemists. The accompanyingpatient information sets have been especially designed to explain thyroid functiontesting and to summarise the main recommendations in the guidelines in everydaylanguage. The purpose of the guidelines is to encourage a greater understanding ofthyroid function testing amongst all stakeholders with a view to the widespreadadoption of harmonised good practice in the diagnosis and management of patientswith thyroid disorders. The guidelines are also intended to provide a basis for localand national audit and each section offers recommendations that are suitable for theaudit process.The document should be considered as guidelines only; it is not intended to serve as astandard of medical care. The doctors concerned must make the management plan foran individual patient. The focus of the document is thyroid function testing, and it isnot intended to be a comprehensive text on thyroid disorders.The process of developmentThe guideline development group met on several occasions. It was agreed to adoptthe literature review accompanying the 2002 publication of The National Academy ofClinical Biochemistry entitled ‘Laboratory support for the Diagnosis and Monitoringof Thyroid Disease’ and to supplement this with publications occurring during andafter 2001. Subgroups took responsibility for individual chapters and the whole groupconsidered each draft. Patient representatives were full members of the developmentgroup throughout the development process.After completion by the development group, the guidelines were subjected to externalrefereeing by individuals with a range of interests, including patients, GP’s,physicians and laboratory specialists in district general hospitals and teaching centresas well as international experts. In addition the draft guidelines were posted on thewebsites of the ACB and BTA, with appropriate links, for a limited period, duringwhich comments were invited and received. Subsequent to this the developmentgroup reviewed the comments and recommendations and appropriate revisions weremade. All members of the group approved the guidelines.5
Mechanism for updatingThe guidelines were completed in June 2006. Comments on their accuracy andrelevance are invited during the first year after publication and should be directed togbeastall@gri-biochem.org.uk. It is intended that a full review will take place afterthree years.Additional informationThe format and style of the guidelines has been modelled on the complementarydocument entitled ‘Guidelines for the Management of Thyroid Cancer in Adults’,which was published in 2002 by The Royal College of Physicians.The British Thyroid Foundation funded the project. No declarations of interest werereceived from any of the professional members of the development group.These guidelines and the accompanying patient information sets may be downloadedfrom the ACB and BTA tion.org6
Types of evidence and the grading of recommendationsThe definition of types of evidence and the grading of recommendations used in theguidelines follows that of the Agency for Health Care Policy and Research (AHCPR),as set out below:Type of evidence (based on AHCPR, 1992)LevelType of evidenceIaIbIIaIIbIIIIVEvidence obtained from meta-analysis of randomised controlled trials.Evidence obtained from at least one randomised controlled trial.Evidence obtained from at least one well-designed controlled studywithout randomisation.Evidence obtained from at least one other type of well-designed quasiexperimental study.Evidence obtained from well-designed non-experimental descriptivestudies, such as comparative studies, correlation studies and casecontrol studies.Evidence obtained from expert committee reports or opinions and/orclinical experience of respected authorities.Grading of recommendations (based on AHRQ, 1994)GradeEvidence levelsDescriptionAIa, IbBIIa, IIb, IIICIVRequires at least one randomised controlled trialas part of the body of literature of overall goodquality and consistency addressing the specificrecommendation.Requires availability of well-conducted clinicalstudies but no randomised clinical trials on thetopic of recommendation.Requires evidence from expert committeereports or opinions and/or clinical experience ofrespected authorities. Indicates absence ofdirectly applicable studies of good quality9Good practice point recommended by guidelinedevelopment group7
RAbTT4TT3UK NEQASµgWHOAmerican Association of Clinical EndocrinologistsAssociation for Clinical BiochemistryAdrenocorticotrophic hormoneAgency for Healthcare Research and QualityAmerican Thyroid AssociationBritish Thyroid AssociationBritish Thyroid FoundationExternal quality assessmentFollicle stimulating hormoneFree thyroxineFree tri-iodothyronineGeneral practitionerHuman anti-mouse antibodyHigh dependency unitImmunometric assayInternal quality controlIntensive therapy unitLuteinising hormoneMinimum detection limitMedullary thyroid cancerMilliunits per litreNational Academy of Clinical BiochemistryNanomoles per litreNon-thyroidal illnessPicomoles per litreProlactinPropylthiouracilRecombinant human TSHRoyal College of PhysiciansRadioimmunoassaySex hormone binding globulinThyroxine, levothyroxineTri-iodothyronineThyroid function testsThyroglobulinThyroglobulin antibodiesThyroid peroxidase antibodiesThyroid stimulating hormone, thyrotrophinTSH secreting pituitary adenomaTSH receptor antibodiesTotal thyroxineTotal tri-iodothyronineUK National External Quality Assessment SchemesMicrogramWorld Health Organisation8
Presentation ConventionsConvention for describing type of evidence and grade of recommendation The AHCPR level of evidence is included both in the main text and in therecommendations of Chapters 2-7 as bold roman numerals I – IV inparentheses. E.g. (III). All recommendations in the guidelines are presented as bullet points withitalic text. At the end of each recommendation the AHCPR level of evidence isincluded and the corresponding grade of recommendation is included as a boldcapital letter A-C in parentheses. E.g. (III,B)Convention for describing thyroxine and tri-iodothyronine Whenever the text refers to the administration of thyroid hormone replacementtherapy the full words thyroxine and tri-iodothyronine are used. Whenever the text refers to the hormones synthesised and secreted by thethyroid gland the abbreviations T4 and T3 are used to describe thyroxine andtri-iodothyronine, respectively. Whenever the text refers to the measurement of thyroxine in serum or otherbody fluids the term FT4 has been adopted. In general this term is intended tosignify that the form of hormone being measured is either free T4 (FT4) ortotal T4 (TT4); wherever this is not the case the text refers to the measurementof the specific form of thyroxine. In 2006, UK NEQAS returns indicate thatthe large majority of UK laboratories measure FT4 in preference to TT4. For the sake of consistency the term FT3 has been adopted to describe themeasurement of either free tri-iodothyronine (FT3) or total tri-iodothyronine(TT3) in serum or other body fluids; wherever this is not the case the textrefers to the measurement of the specific form of tri-iodothyronine. In 2006,UK NEQAS returns indicate that roughly equal numbers of UK laboratoriesmeasure FT3 and TT3.Convention for recording numerical data At several points in the text numerical results are presented (e.g. ‘a TSH levelof 10mU/L). These numerical results should be regarded as typical targetfigures rather than as absolute cut-offs. The historical nature of some of theevidence base together with uncertainty of the bias of the assays used in theolder studies means that absolute cut-offs cannot be presented. Individuallaboratories should use external quality assessment and other data to determineif bias-related cut-offs are appropriate for the methods that they use. However,in most cases it is unlikely that laboratories will have sufficient data to achievean accurate adjustment of the TSH cut-offs quoted in these guidelines.9
AcknowledgementsGrateful thanks are expressed to: The British Thyroid Foundation for funding the project The Association for Clinical Biochemistry for hosting the meetings of theguidelines development group The Executive Committee of the British Thyroid Association for helpfulcomments during the formulation of the guidelines The individuals behind the 33 responses that were received as a result of theconsultation exercise10
1.Introduction1.1Thyroid disordersThyroid disorders are amongst the most prevalent of medical conditions, especially inwomen. Disorders of the thyroid include both overt and mild/subclinicalhypothyroidism and hyperthyroidism, goitre and thyroid cancer.Hypothyroidism is an insidious condition with significant morbidity and the subtleand non-specific symptoms and signs may be mistakenly attributed to other illnesses,particularly in post-partum women and the elderly. In iodine-replete communities thecause is normally either chronic autoimmune disease (atrophic autoimmunethyroiditis or goitrous autoimmune thyroiditis (Hashimoto’s thyroiditis)) ordestructive treatment for hyperthyroidism, which may account for up to one-third ofcases of hypothyroidism in the community. The prevalence of spontaneoushypothyroidism is 1-2%; it is more common in older women and ten times morecommon in women than in men.1Hyperthyroidism has a significant short-term morbidity and long-term morbidity andmortality. The most common causes of hyperthyroidism in iodine-repletecommunities are autoimmune Graves’ disease and toxic multinodular goitre andwhilst rarer causes include excessive thyroxine replacement, an autonomouslyfunctioning thyroid adenoma, or thyroiditis. The prevalence of hyperthyroidism inwomen is 0.5-2% and is also ten times more common in women than in men.11.2Thyroid Function Tests (TFT)Thyroid disorders are common and so thyroid function testing in blood samples isalso common with approximately 10 million requests each year in the UK at anestimated cost of 30 million.2 The most commonly performed tests in serum areused to establish if there is thyroid dysfunction or to monitor the response to therapy.These tests include thyroid stimulating hormone (TSH), free thyroxine (FT4), and freetri-iodothyronine (FT3). A range of other tests is also available to determine thespecific causes of thyroid disease.The majority of thyroid disorders present to and are managed initially within GeneralPractice. Specialist thyroid physicians, who are usually hospital-based ClinicalEndocrinologists, and surgeons are involved at a later stage in many cases. Virtuallyall thyroid function testing currently takes place in hospital laboratories indepartments of Clinical Biochemistry. Therefore, there are three main stakeholders inthyroid function testing: The patient The physician (GP and specialist) The laboratory1.3The Patient Perspective11
Patients are becoming more informed about their health and any disorders from whichthey suffer. They obtain this information from doctors, from patient supportorganisations and from the Internet. There is a huge amount of information availableabout thyroid disease but it can be confusing and it is not always consistent in termsof content or implementation. Patients find it difficult to understand that the diagnosisof thyroid disease is not always clear-cut or that individual patients responddifferently to treatment. They have an expectation that thyroid function testing acrossthe UK is uniform in terms of the tests performed, the results obtained and theinterpretations made. Some of the questions most frequently asked by patients arelisted in Table 1.1.1.4The Physician PerspectiveThe symptoms of thyroid disease can be relatively non-specific and one of the firstchallenges for the GP is to consider thyroid disease in the differential diagnosis of thesymptoms of the individual patient. Once this consideration has been made the GPwould like TFT either to exclude or confirm the diagnosis of thyroid disease. Forborderline cases the GP expects the laboratory to provide the combination of TFT thatprovide the maximum information and they welcome an interpretation of the results indifficult cases. For patients known to have thyroid disease GPs expect TFT to provideinformation that assists with the optimisation of therapy. Some of the questions mostfrequently asked by GPs are listed in Table 1.2a. Many laboratories provideinterpretive comments to GPs on all abnormal TFT results and user surveys indicatethat this service is appreciated.The specialist thyroid physician receives referrals from GPs and from other sources.In all cases the job of the thyroid physician is made much easier when the referralnotes include results of appropriate TFT performed at appropriate times. The thyroidphysician expects the laboratory to deliver a comprehensive range of TFT withanalytically valid results and finds it difficult to understand why laboratories offerdifferent test profiles and why results are not always transferable betweenlaboratories. Some questions most frequently asked by thyroid physicians are listed inTable 1.2b.1.5The Laboratory PerspectiveThyroid function testing is relatively expensive and laboratory budgets have struggledto cope with the rapidly rising number of TFT over the last few years. Clinicalbiochemists wish to work with physicians to ensure that all requests for TFT arejustified on clinical grounds and that there is not unnecessary repetition. They alsostrive to obtain sufficient clinical information with each request to ensure that theyprovide the optimal combination of TFT for each patient without performingunnecessary or misleading tests. Some of the questions most frequently asked byclinical biochemists are listed in Table 1.3.1.6The Need for National Guidelines12
It is clear from the previous sections that the different stakeholders are uncertainabout many aspects of thyroid function testing. Therefore, the need for nationalguidelines for something as common as thyroid function testing is self-evident.However, such guidelines do not exist in the UK, the nearest being the referencesgiven to testing as part of the consensus statement for good practice and auditmeasures in the management of hypothyroidism and hyperthyroidism.3 In the USAthe American Thyroid Association (ATA) has published guidelines for detection ofthyroid dysfunction 4; the ATA and the American Association of ClinicalEndocrinologists (AACE) have published guidelines on subclinical thyroid disease 5;and the National Academy of Clinical Biochemistry (NACB) has published practiceguidelines on the laboratory support for the diagnosis and monitoring of thyroiddisease.6 However, none of these two sets of guidelines addresses the subject ofthyroid function testing from the perspective of all three stakeholders and neither usesthe rules of evidence based medicine 7 to support the recommendations.As a result, the Association for Clinical Biochemistry (ACB), the British ThyroidAssociation (BTA) and the British Thyroid Foundation (BTF) agreed to take theinitiative to produce a set of evidence-based guidelines that meet the requirements ofall three stakeholders. The model used for guidelines production has been thatemployed by the BTA and the Royal College of Physicians (RCP) in the recentlypublished guidelines for the management of thyroid cancer.8Table 1.1 Questions Frequently Asked by PatientsWhat is a thyroid function test?Why should I have a thyroid function test?What do the results of thyroid function tests show?What is the difference between a normal range and a reference range?I didn’t have any tests until after I had thyroid disease, how does my doctor knowwhat is the normal range for me?Why do blood tests and ranges differ throughout the country?If my test results are abnormal will I be referred, and to whom?Can I arrange to have a private blood test?Can I buy a kit to do my own thyroid function testing?Why don’t thyroid function tests always give clear-cut answers?What do the terms sub-clinical and borderline mean?Will I get treated if my results are borderline?How does pregnancy/menstruation/the pill/HRT affect my test results?Can my diet affect my test results and should I fast before testing?Does the number of hours after my thyr
Purpose of the guidelines . thyroid function testing amongst all stakeholders with a view to the widespread adoption of harmonised good practice in the diagnosis and management of patients with thyroid disorders. The guidelines are also intended to provide a basis for local . The historical nature of some of the
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