1. Thyroid Disease When to test for thyroid dysfunction
Have a low index of suspicion
You should expect negative tests in at least 90% of patients (apologies to Dr Colley)
But beware of attributing symptoms to mildly abnormal thyroid function tests
Unexplained fatigue, weight change, disturbance of mood, cardiac arrhythmia especially atrial fibrillation, change in bowel habit, change in temperature preference etc
Ideally do not test in the acute phase of the illness “sick euthyroid syndrome”

2. Odd Thyroid Function Tests Low but not suppressed TSH 0. 1 (ie above 0
Usually of no significance
Measure Free T4 and Free T3 and if normal just follow tests

3. Odd Thyroid Function Tests Suppressed TSH (0. 03 or at least <0
Odd Thyroid Function Tests Suppressed TSH (0.03 or at least <0.1) with normal Free T4
Check T3
If normal:
In young patients follow up closely
In patients over 50 seek evidence of nodular thyroid disease and then treat

4. Odd Thyroid Function Tests Normal TSH, high Free T4
Could be due to acute medical or psychiatric illness,
Medication
Levothyroxine Replacement
Oestrogens (Pregnancy)/Tamoxifen/Raloxifene
Amiodarone

5. Odd Thyroid Function Tests Low but not suppressed TSH (eg 0
Odd Thyroid Function Tests Low but not suppressed TSH (eg 0.2) with low T4
Non thyroidal illness
Secondary hypothyroidism (pituitary disease)

6. Odd Thyroid Function Tests High TSH, high Free T4 (sometimes high Free T3)
Possible explanations:-
Poorly compliant patient with primary hypothyroidism on Thyroxine taking extra doses of Thyroxine prior to blood test!
TSH Receptor Resistance
Pituitary TSHoma

7. Odd Thyroid Function Tests Suppressed TSH (<0.03) with low Free T4
Usually found in the early stages of treatment in patients with Carbimazole (or Propylthiouracil) where TSH is not a good marker of thyroid function

8. Odd Thyroid Function Tests Sl High TSH (<10), Normal Free T4
Common : up to 10%
May be normal… don’t rush into replacement! Sl high TSH drive maintains normal levels.
Chronic thyroiditis (may be resolving)
Repeat 2-3m
If thyroid autoantibodies +ve approx 5% pa become hypothyroid

9. “Thyroid Dysfunction” with normal thyroid function tests.
Usually symptoms are not(and sometimes never were) due to thyroid dysfunction
Many patients feel better on treatment with excess Thyroxine
Avoid over treatment with Thyroxine:
Increases risks of cardiac arrhythmias and death, accelerates bone mineral loss
Beware of the placebo effect / Avoid quacks and the internet
No evidence that serum TSH is inaccurate in primary hypothyroidism (urine tests not validated)
Good evidence base that T4 with T3 is no better than T4 alone

10. Management of Hypothyroidism
Treat if repeated TSH is > 10 especially if thyroid microsomal antibodies are significantly positive (>1:1,600)
Beware of promising long term cure for vague symptoms in mild hypothyroidism
Unless cardiac disease
T4 5-8, TSH 10-20:start Levothyroxine 50mcg
T4 3-5, TSH >20: start Levothyroxine 100mcg
T4 <3, TSH >20: start Levothyroxine 125mcg
If co-existent cardiac disease refer
Consider that hypothyroidism may be temporary if post partum (or thyroiditis)
Keep TSH in the lower part of the reference range (0.5 to 2.5)
Thyroxine requirements increase on average 40% in pregnancy
Thyroxine requirements may increase with progressive thyroid failure

11. Pitfalls
If on replacement following thyroid cancer, high doses to ensure complete suppression used
Thyroxine requirements may increase with progressive thyroid failure.
If they need high doses consider:
Compliance
Big people often need big doses
Absorption
Atrophic gastritis/helicobacter positive: change in requirements after treatment.
Coeliac

12. Management of Hyperthyroidism I
Consider viral thyroiditis if marked systemic symptoms (out of proportion to the degree of thyrotoxicosis) or/and pain/tenderness in the neck
Commence:
Carbimazole 20 mgs daily for mild thyrotoxicosis (Free T4 <35)
30 mgs daily moderate thyrotoxicosis (Free T )
40 mgs daily for severe thyrotoxicosis (Free T4 >60)
Only give Propranolol or other betablockers if req for Sx control

13. Management of Hyperthyroidism II
Counsel about smoking – serious thyroid eye disease five times commoner in smokers
Check blood count before treatment and routinely once more thereafter only if serious infection (sore throat)
Counsel patients about side effects of drugs including weight gain and delay in resolution of affective symptoms
Free T4 comes down before Free T3 with treatment, TSH remains suppressed for many weeks/months (avoid measuring in the early weeks of treatment)

14. Pitfalls
Remember to warn about s/e CBZ : agranulocytosis (3:10,000 usu first 3m)
If levels not responding as expected:
was this a thyroiditis?
Long term treatment and compliance may be an issue (nb wt)
Vomiting may be s/e of Rx or condition: affects absorption
TSH remains suppressed for a long time: measure T4 +/- T3
Unexpected return of fertility

15. Pitfalls Smoking increases risk of thyroid eye disease
Fluctuating levels can worse TED
Low dose aspirin for >50s until TSH normalises
AF high risk
In thyrotoxicosis, digoxin metabolism increased: higher doses

16. Pitfalls
Very occasionally after I131 can become more thyrotoxic temporarily
Amiodarone: initial levels: T4 incr, T3 decr, TSH incr then normalise