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Thyroid Testing Strategies in the South-West and Wessex

A survey conducted on behalf of the ACB SW&W Regional Committee by

Roberta Goodall

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Survey Structure and Responses

• Questionnaire e-mailed to audit leads • 24 laboratories surveyed

– 13 South West, 11 Wessex– 2 known 'pairs' (ie shared protocol/testing)– 1 assumed pair– 21 expected responses

• 20 questionnaires returned

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Test SW labs Wessex labs Total

TSH only 9 5 14

TSH + fT4 1 4 5

TSH + fT3 1 1

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Q1. What is (are) your frontline test(s) for thyroid function?

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Q2. What are your reference ranges?

Nearly all different – even with same instrument

Ranges below show lowest quoted lower limits with highest upper limits

TSH mU/L fT4 pmol/L fT3 pmol/L

0.03 – 6.9 7 – 26 to 7.8*

Smallest 0.27 – 4.2 10 – 20 4.0 – 6.8 (2.5-5.3)

Largest 0.3 – 6.0 7 – 26 3.2 – 7.8

* One lab goes as high as 8.8 on an age related range (<40yrs)

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Q3. Do you perform reflex testing?

'No'

TSH+fT4 3/5

'Yes'

TSH only 14/14

TSH+fT4 2/5

TSH+fT3 1/1

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Q3. What is/are the rule(s) and the reflex analyte(s)?

Based on front–line result

TSH TSH/fT4 TSH/fT3

TSH low – add fT4 9TSH low – add fT3 5 1TSH high – add fT4 10fT4 high – add fT3 1Low TSH, on T4 – add fT4 2Persistent elevated TSH – add TPO 1

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Q3. What is/are the rule(s) and the reflex analyte(s)?

• Frontline can change based on certain criteria, for example• Paediatric patients always get both – 7/20 respondents• Certain consultants get fT4 frontline (or whatever they ask for) –

1(2)/20

• Clinical information will change request – 2nd line rather than reflex? – too many to list but e.g

• Differentiation made between diagnostic testing (TSH only) and known disease

• fT4 added to both treated hypos and hypers• fT4 (and fT3) added to hypopit

• Concomitant therapy eg amiodarone, Li, get fT4 (and fT3) regardless• All rules / protocols can change at the discretion of the signer at

clinical validation.

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Q3. How is it / are they activated?

17 / 20 perform (rule based?) reflex testing

Automatically by computer/analyser 4

At technical validation by BMS 1

At clinical authorisation 3

Basic rule auto / extras at validation 8

Basic rule at TA / extras at validation 1

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Q3. What proportion cascade to a second line test?

0 – 10% 7 (4 were < 5%)

11 – 20% 5

21 – 30% 2

31 – 40% 1

41 – 50% 0

51 – 60 % 1

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Q4. Do you have criteria for requesting / analysing thyroid antibodies and, if so, what are they and

which antibodies do you perform / request?

No criteria (or other explanation) 3

Done elsewhere (no other information given) 1

TPO antibody 11

Anti-T4 1

TSH receptor antibodies 1

Type not stated (assume TPO) 3

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Criteria for TPO (14/16)(recommended, suggested, requested)

TSH TSH/fT4 TSH/fT3

Borderline / slight TSH (usually on rpt) 3 2 1

TSH (persistent/gross, discretion of signer) 1

Not defined (discretion of signer) 2

Rarely / not suggested 1

Suspicious/mismatched results 1

Sub-clinical / compensated hypo 2 1

Q4. Do you have criteria for requesting / analysing thyroid antibodies and, if so, what are they and

which antibodies do you perform / request?

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Q5. What analytical platform do you use for your thyroid function tests?

TSH TSH/fT4 TSH/fT3

Roche Elecsys 1 1

Bayer Centaur 4 3

DPC Immulite 3 1

Roche Modular 3

Beckman Access + IMX 1

Abbott AxSym 1

Immuno 1 2

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Q6. What is your annual TFT workload?

Number of TFT requests (1000s pa)

TSH TSH/fT4 TSH/fT3

20 – 30 2

30 – 40 1 1

40 – 50 5 1

50 – 60 1

60 – 70 4 1

70 – 80 1

80 – 90 1

90 – 100 1 1

100 – 110 1

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Q7. - any comments?

• ' ….remain unconvinced of the need to go over to dual

frontline. This would cost an additional £60K/year, plus the

need for another analyser. fT4 is also more of a problem

assay and if always done could lead to more patients being

investigated for possible hypopit at considerable extra cost.'

• ' ? dual front-line vs TSH only must be a quality, not a cost

issue'

• ' we have always performed fT4 and TSH frontline. We pick

up approx 6-8 hypopit pts/year (38,000 requests pa) that

would otherwise be missed using TSH alone'

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• 'Not averse to frontline TSH. Would however miss some

hypopit. + miss other relevant findings eg if anti-thyroid

drug therapy not recorded

• 'We wish to introduce frontline fT4 plus TSH (in line

with current guidelines) but have not had success getting

funding although we are supported by our

endocrinologist.

• 'The reasons for not having dual front line TSH and fT4

on all samples are largely economic.'

Q7. - any comments?