Standards for Thyroid Function Testing Strategies

[Guest guest]

Cannot remember whether I posted the following to our

members. This is useful to print off and take to your doctor if he refuses to

test TSH only.

Luv - Sheila

All Wales Clinical Biochemistry Audit

Group

Standards for Thyroid Function Testing

Strategies

INTRODUCTION

The results of a questionnaire sent to all

laboratories in Wales in September 1999 revealed significant differences in

thyroid function testing strategies between laboratories. The majority (9/14)

of laboratories used a first line thyrotropin (TSH) and free thyroxine (FT4)

strategy, 4 laboratories used TSH alone and 1 laboratory used FT4 alone. Some

of the strategies for further testing were unnecessarily complex.

Many guidelines for the detection of thyroid

disease recommend a first-line TSH-only strategy.1,2 However, a TSH-only

strategy may miss cases of secondary and tertiary hypothyroidism 3,4,5 as the

presenting clinical features of pituitary and hypothalamic disease are often

non-specific. A TSH-only strategy may also miss cases of primary

hyperthyroidism (G.Beckett, personal communication), as immunoassays remain prone

to interference, especially from heterophile antibodies.6,7

The survey showed that many laboratories

experienced problems with inappropriate testing (11/13) and excessive

repetition of testing (10/13). While method-related differences in reference intervals

were expected, even those quoted by laboratories using the same methodology

were different. It is often impractical for laboratories to validate reference

intervals on their own, but a multicentre approach for deriving them for

thyroid hormones using identical analysers has been proposed.8

The following standards are therefore

recommended in the light of the survey findings, discussion at audit meetings

in November 1999 and April 2000 and published evidence.

STANDARDS

1. All laboratories offering thyroid function

tests should provide TSH and FT4 assays “on site”

and should provide or have access to assays

for free tri-iodothyronine and thyroid antibodies.

TSH should be measured by at least a second

generation immunoassay with a functional

sensitivity down to 0.02 mU/L.

2. It is recommended that all laboratories

should use a TSH and FT4 first-line testing strategy.

3. Laboratories should have a clearly

documented strategy for further testing, which should be

as simple and explicit as possible. The

strategy should be agreed with local physicians and

endocrinologists. It is recommended that the

strategy should utilise only first-line test results,

previous results and clinical information.

4. It is recommended that measurement of

thyroid peroxidase (TPO) antibodies9 is generally

sufficient when antibody testing is required

to investigate suspected autoimmune thyroid

disease; thyroglobulin antibodies do not need

to be routinely measured. It is recommended

that TPO antibodies are measured using an immunoassay

technique; haemagglutination

methods have inadequate sensitivity and

specificity.

5. All laboratories should use validated

reference intervals. Laboratories using the same

method should endeavour to adopt common

reference intervals.

6. Laboratories should comment on abnormal

results where appropriate, especially for general practitioners and other

non-expert clinicians.

7. Laboratories should endeavour to

discourage inappropriate and unnecessary repeat testing.

8. Laboratories should be aware of potential

analytical interferences (e.g. heterophile antibodies) and either investigate

problems “on site” or refer samples to other laboratories for

checking.

9. Laboratories should ensure that

appropriate internal quality control (IQC) and external quality assessment

(EQA) procedures are in place for each assay they perform.

REFERENCES

1. Ladenson PW, Singer PA, Ain KB, et al.

American Thyroid Association Guidelines for the

detection of thyroid disease. Arch Intern Med

2000; 160: 1573-1575.

2. Bauer DC, Brown AN. Sensitive thyrotropin

and free thyroxine testing in outpatients. Are

both necessary? Arch Intern Med 1996; 156:

2333-2337.

3. Waise, A, Belchetz PE. Clinical review:

Lesson of the week. Unsuspected central

hypothyroidism. Testing only for thyroid

stimulating hormone will miss unsuspected cases of

central hypothyroidism. BMJ 2000; 321:

1275-1277.

4. Wardle CA, Fraser WD, Squire CR. Pitfalls

in the use of thyrotropin concentration as a firstline thyroid-function test.

Lancet 2001; 357: 1013-1014.

5. Dayan CM. Interpretation of thyroid

function tests. Lancet 2001; 357: 619-624.

6. Selby C. Interference in immunoassay. Ann

Clin Biochem 1999; 36: 704-721.

7. Ismail AAA, Barth JH. Wrong biochemistry

results. (editorial) BMJ 2001; 323: 705-706.

8. CE, Hanning I, McBain AM, Moody D,

Price A. A model for a multicentre approach to the derivation of reference

intervals for thyroid hormones and testosterone for laboratories

using identical analysers. Clin Chem Lab Med

2000; 38: 1013-1019.

8. tti S, Caturegli P, Piccolo P, et al.

Antithyroid peroxidase autoantibodies in thyroid

diseases. J Clin Endocrinol Metab 2000; 71:

661-669.

ACKNOWLEDGEMENTS

Mr.I.Hanning, Dr.I.Hainsworth and Dr.R..

VERSION: 1

DATE: 11 January 2005

Appendix: Calendar of Audit Process for

Standards for Thyroid Function Testing Strategies

Nov. 1999 Findings of a survey of Welsh

laboratories’ strategies for thyroid function testing (14/14 laboratories

replied) undertaken by Dr.I.Hainsworth (Consultant Biochemist, ton

Hospital, Swansea) and presented at a joint Wales/South West England Clinical

Biochemistry Audit meeting in Weston-super-Mare on 18th November 1999. 2000-2001

Initial draft standards prepared by Dr.I.Hainsworth and then modified by

Mr.I.Hanning (Consultant Biochemist, Hull Royal Infirmary) following

Dr.Hainsworth’s retirement.

Additional advice provided by Dr.R.

(Consultant Biochemist, University Hospital of Wales, Cardiff). Draft standards

reviewed at All Wales Clinical Biochemistry Audit Group committee meetings.

2001 Draft standards sent for consultation to

consultant biochemists and endocrinologists in Wales to seek their views. Final

draft of standards presented at the All Wales Clinical Welsh Biochemistry Audit

Group meeting on 18th October 2001 and at the Welsh Endocrine and Diabetes

Society business meeting on 1st November 2001. Nov. 2001 Standards finalised

and ratified at an All Wales Clinical Biochemistry Audit Group committee

meeting (on 22nd November 2001) by Dr.K.Griffiths (chairman).

2005

Proposed date of re-audit and review of standards

http://www.acbwales.org.uk/audit/guidelines/tft_stds.pdf